DTU ProjectLab - User contributions [en-gb]

Talk:Program evaluation and review technique (PERT)

2015-09-28T18:48:51Z

S141938:

Anna: Very nice topic! It seems that you have a good grasp on the structure of the article and the theme fits the first article type: method :).

== Reviewer 1 - Biankajuh: Feedback==
# I have find your abstract very well-designed which fulfill the role of introducing the main purpose and highlights of the article. Also commendable that you mention the limitation of the PERT model and talk about the comparative tools as well as the modifications.
'''Answer''' : Extendended the last sentence a bit.
# The article is nicely illustrated with the pictures which help the understanding. Although, I would suggest to name them as ‘’Figure 1, 2, 3, …etc.’’ which would allow to refer to the pictures more specifically. So for example instead of the sentence “This information is presented in a box representation.”, you could say “This information is presented in the box representation showed in Figure 1.”.
'''Answer''': Added the figure numbering and some references in the text to the figures.
#The third figure entitled in “PERT network in MS Project 2013” is quite unclear. Could you increase the quality of the picture?
'''Answer''': Changed it (that's the best I can get)
#In some cases, too long sentences could be substituted by two or three shorter ones to help the understanding. For example: “The essential difference between a PERT chart and DSM is the visualization; DSM matrices represent basically the same information as a PERT network, which is different activities and their connections; the advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network.” (Comparison to other tools) —> Could be changed to: “The essential difference between a PERT chart and DSM is the visualization. DSM matrices represent basically the same information as a PERT network, which is different activities and their connections. The advantage of this representation in DSM is its conciseness compared to PERT, where lots of space is required to have a readable network.”
'''Answer''': I have made a few changes, wherever I could.
#Grammatical/Formatting hints:
##Space missing between two sentence: “whereas the events are the nodes.For instance,” (Network diagram),
'''Answer''': Added
##No need for space before question mark: “How do they differ from eachother ?” (Comparison to other tools)
'''Answer''': Changed it, but did'nt know it was an 'error'
#Regarding the Bibliography, I would note to refer all these references within the text of the article at the corresponding spaces.

'''Reviewer 2 – User: s113735'''
Feedback: Program evaluation and review technique (PERT)
Formal Aspects:
*The article clearly follows the “method or tool” structure required. Super!
*The grammar and spelling in the article is at a decently high level. The sentences are short and concise, which makes it a pleasurably read with clear and easy to understand points.
'''Answer''': Thanks ;)
*Your choice of figures are good and in line with the points, you are trying to make. Some figures could, however, be explained a little better (for instance the PERT box).
'''Answer''': I have explained everything that is contained in the PERT box
*Figures are missing references.
'''Answer''': Applied changes
*The article has a bibliography, but is otherwise free of references and links. This makes it really hardto check the validity of your points. The article will have to be referenced.

Content Aspects:
*The article is clearly within the scope as it relates directly to a “Program” tool/method.
*The length of the article seems fair, but a few headings and sub-sections could easily be elaborated a bit. (For instance the “process” section: What are the benefits/drawbacks from using the tools you present? Are the tools prescribed or optional? Etc… You explain the overall applications and limitations for the PERT model, but not for the individual tools).
'''Answer''': My remarks to the PERT model takes into account the limitations and benefits of each tool. I think I might simply repeat myself if I specify these ahead. Plus, the reader might get a bit lost.

*The “critical path” in Project Management to my knowledge is not “the path that includes the most time consuming tasks” but is instead “the sequence of activities which add up to the longest overall duration”. You clearly show in your article that you know this while ALSO showing you know how to calculate the critical path.
'''Answer''': Applied your suggestion. Thanks ;)
*With a little bit sharper terminology and definitions, it would increase the understanding a lot.
*When making a statement like: “But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures.” This definitely need to be referenced.
Other than in a few cases the article is generally void of personal/unverifiable opinions, which is good.
*So far, the article doesn’t link to any other articles on the Wiki. I understand that it might be tough to find something directly related to this specific tool amongst the rather limited topics on the Wiki. I suggest trying to find some broad topics or even Categories to link to when writing. For instance, you might link to “human behaviour” (a category on the Wiki) when writing about the “agreement dimension” in the Stacey Matrix.
'''Answer''': Links added

Overall Conclusion: The article is written at a high level and is easy to read and understand. Some points could however be elaborated a bit and the article needs to be referenced according to Wiki standards using the
<nowiki><ref> lastname, firstname (year) [www.link.com “linkname”] </ref></nowiki> standard.
'''Answer''': All of the content content comes from various books treating about this method. The difference between those books are details and the way the knowledge is passed, so it would be a bit hard for me to reference each piece, since it would have to be referenced to most of them

== MistaJacob, reviewer 3 ==

=== The feedback will be given in the form: ===
*My feedback
**My feedback

OR

*’’Copy of your text’’
**My feedback

=== Feedback ===
*The general formatting is almost as it’s supposed to be. The pictures though lack the numbering and the references in the text, and you shift with using ‘thumbs’ and placing it in the middle. Consistency can be recommended for a better visual overview.
'''Answer''': It is true. I have moved all of the pictures to the right and reduced their sizes to have a nicer layout.
*The language is clear and easy to read, only with small number of places where i found typo’s, like in “Limitation” where you start and end a sentence with: Therefore
**I will not comment these since they will be obvious to you when you read through your article for corrections.
'''Answer''': Corrected

*I found the article relevant, with a good red thread through it.
*The step by step approach worked as it should. That being said, the reader’s understanding could have been improved if you included a practical example you carried out through all steps
**As you promised in the introduction :)
'''Answer''': TO DO
*in the section “Key Concepts”, the sequence of the bullet point list should be the same as the sequence in which they are explained, or vice versa.
*’’The process of making a PERT analysis can be divided into 4 steps:’’
**you have written 5 bullet points below
'''Answer''': Good eye ;)

*‘’Preparation of a list of all the tasks that will be involved in a given project’’
**I would stick to using ‘activities’ and not ‘tasks’ as you write here.
'''Answer''': True, especially that activties is a word that I have put in the key concepts

**There are other places (maybe only one) where you use task as well
'''Answer''': changed it everywhere

*I would suggest that you also explain the term ‘float’, since it appears in your figure
'''Answer''': I was going to explain the box a bit more.

*‘’In this step we estimate the amount of time that can be taken by each activity.’’
**You normally don’t use ‘we’
'''Answer''': My bad.

*‘’A project cannot be completed as long as his longest component isn't finished.’’
**Don’t know whether you would be able to argue your way out of defining a project as being ‘male’ ;)
*‘’Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project.’’
**Double up
'''Answer''': Corrected.
*Since you describe the other tool in the comparison very briefly, I would suggest to include links to their respective articles (if they exists)
'''Answer''': Done

Program evaluation and review technique (PERT)

2015-09-28T18:39:11Z

S141938: /* Bibliography */

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects, its advantages and limitations.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

The '''activities''' are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The '''events''' are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

A '''network diagram''' is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The '''critical path''' is the sequence of activities which add up to the longest overall duration. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 5 steps:
* Preparation of a list of all the activities that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

[[File:PERT box.png | thumb | right | 300px | '''Figure 1''': PERT box ]]

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation showed in figure 1. This box will later be filled with other time informations about the project. For instance the earliest start time, which is self-explanatory, is the time when the earliest date for an activity to be started. This goes in pair with the earliest finish - earliest date when the activity can be finished. These two timings report the most optimistic scenario and aren't usually met. The same logic applies to the latest times, but those are considered as the pessimistic time. More about these times will be later. Float is basically the difference between the earliest times and the latest. Its purpose is too give an overview of the timing margin that a certain activity has.

=== Network diagram ===

[[File:PERT network.png | thumb | right | 300px | '''Figure 2''': PERT network with critical path ]]

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the activity and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes just like on figure 2. For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

=== Estimation of the time ===

In this step, the amount of time that can be taken by each activity is estimated. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as its longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the activities which have a null difference between the respective times. Those activities constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between activities
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager.
* No representation of repetitive activities. Because the project is presented in a network form, a repetitive activity would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:PERT network in ms Project.png | thumb | right | 300px | '''Figure 3''': PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project (see figure 3) or Oracle Primavera. PERT charts are used to visualize the dependencies between different activities. To see the timing and progress of the project another similar tool is widely used, the [[ The Gantt chart and the usage nowadays | Gantt charts ]]. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 300px | '''Figure 4''': Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the [[ The Critical Path Method (CPM) | Critical Path Analysis ]], the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization. In the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities and progress of the project (see figure 4). Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

'''Design Structure Matrix''' (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization. DSM matrices represent basically the same information as a PERT network, which is different activities and their connections. The advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network (see figure 5). However it doesn't give any information concerning timings of activities. It is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | right | 300px | '''Figure 5''': DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== See also ==

* [[ Responsibility Assignment Matrix (RACI Matrix) ]]
* [[ Scheduling techniques in Project Management ]]
* [[ Critical chain project management (CCPM) ]]
* [[ Critical Path Method in Construction Industry ]]
* [[ Critical Chain Project Management ]]
* [[ Metra Potential Method ]]
* [[ The Critical Path Method (CPM) ]]

== Bibliography ==

# ''ESSENTIALS OF MANAGEMENT'', Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
# ''Programming and Scheduling Techniques'', Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
# ''The Handbook of Project Management: A Practical Guide to Effective Policies'', Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
# ''Entrepreneurship Development'', S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
# https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
# ''Project Management Demystified: Today's Tools and Techniques'', Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.
# https://www.mindtools.com/critpath.html, comparison of the PERT method and CPA
# ''Program evaluation and review techniques II (PERT II)'', Yakhchali, Siamak Haji, 2011, Discussion about the PERT II methodology, which introduces a stochastic approach to determine the time of an activity
# ''The project schedule management model based on the program evaluation and review technique and Bayesian networks'', Zhao, Zhigang; Jin, Yong, 2011. Presents the usage of Bayesian networks to determine the probability of the time of a certain activity.
# ''RPERT: Repetitive-projects evaluation and review technique'', Aziz, Remon Fayek, 2014. Presents a modified version of PERT, and a sample software implementation that enables the usage of this method. The software takes care of the calculations of the times.

Program evaluation and review technique (PERT)

2015-09-28T18:09:12Z

S141938: /* Bibliography */

Program evaluation and review technique (PERT)

2015-09-28T17:58:57Z

S141938: /* Bibliography */

Talk:Program evaluation and review technique (PERT)

2015-09-28T17:51:32Z

S141938:

Anna: Very nice topic! It seems that you have a good grasp on the structure of the article and the theme fits the first article type: method :).

== Reviewer 1 - Biankajuh: Feedback==
# I have find your abstract very well-designed which fulfill the role of introducing the main purpose and highlights of the article. Also commendable that you mention the limitation of the PERT model and talk about the comparative tools as well as the modifications.
'''Answer''' : Extendended the last sentence a bit.
# The article is nicely illustrated with the pictures which help the understanding. Although, I would suggest to name them as ‘’Figure 1, 2, 3, …etc.’’ which would allow to refer to the pictures more specifically. So for example instead of the sentence “This information is presented in a box representation.”, you could say “This information is presented in the box representation showed in Figure 1.”.
'''Answer''': Added the figure numbering and some references in the text to the figures.
#The third figure entitled in “PERT network in MS Project 2013” is quite unclear. Could you increase the quality of the picture?
'''Answer''': Changed it (that's the best I can get)
#In some cases, too long sentences could be substituted by two or three shorter ones to help the understanding. For example: “The essential difference between a PERT chart and DSM is the visualization; DSM matrices represent basically the same information as a PERT network, which is different activities and their connections; the advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network.” (Comparison to other tools) —> Could be changed to: “The essential difference between a PERT chart and DSM is the visualization. DSM matrices represent basically the same information as a PERT network, which is different activities and their connections. The advantage of this representation in DSM is its conciseness compared to PERT, where lots of space is required to have a readable network.”
'''Answer''': I have made a few changes, wherever I could.
#Grammatical/Formatting hints:
##Space missing between two sentence: “whereas the events are the nodes.For instance,” (Network diagram),
'''Answer''': Added
##No need for space before question mark: “How do they differ from eachother ?” (Comparison to other tools)
'''Answer''': Changed it, but did'nt know it was an 'error'
#Regarding the Bibliography, I would note to refer all these references within the text of the article at the corresponding spaces.

'''Reviewer 2 – User: s113735'''
Feedback: Program evaluation and review technique (PERT)
Formal Aspects:
*The article clearly follows the “method or tool” structure required. Super!
*The grammar and spelling in the article is at a decently high level. The sentences are short and concise, which makes it a pleasurably read with clear and easy to understand points.
'''Answer''': Thanks ;)
*Your choice of figures are good and in line with the points, you are trying to make. Some figures could, however, be explained a little better (for instance the PERT box).
'''Answer''': I have explained everything that is contained in the PERT box
*Figures are missing references.
'''Answer''': Applied changes
*The article has a bibliography, but is otherwise free of references and links. This makes it really hardto check the validity of your points. The article will have to be referenced.

Content Aspects:
*The article is clearly within the scope as it relates directly to a “Program” tool/method.
*The length of the article seems fair, but a few headings and sub-sections could easily be elaborated a bit. (For instance the “process” section: What are the benefits/drawbacks from using the tools you present? Are the tools prescribed or optional? Etc… You explain the overall applications and limitations for the PERT model, but not for the individual tools).
*The “critical path” in Project Management to my knowledge is not “the path that includes the most time consuming tasks” but is instead “the sequence of activities which add up to the longest overall duration”. You clearly show in your article that you know this while ALSO showing you know how to calculate the critical path.
'''Answer''': Applied your suggestion. Thanks ;)
*With a little bit sharper terminology and definitions, it would increase the understanding a lot.
*When making a statement like: “But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures.” This definitely need to be referenced.
Other than in a few cases the article is generally void of personal/unverifiable opinions, which is good.
*So far, the article doesn’t link to any other articles on the Wiki. I understand that it might be tough to find something directly related to this specific tool amongst the rather limited topics on the Wiki. I suggest trying to find some broad topics or even Categories to link to when writing. For instance, you might link to “human behaviour” (a category on the Wiki) when writing about the “agreement dimension” in the Stacey Matrix.
'''Answer''': Links added

Overall Conclusion: The article is written at a high level and is easy to read and understand. Some points could however be elaborated a bit and the article needs to be referenced according to Wiki standards using the
<nowiki><ref> lastname, firstname (year) [www.link.com “linkname”] </ref></nowiki> standard.
'''Answer''': All of the content content comes from various books treating about this method. The difference between those books are details and the way the knowledge is passed, so it would be a bit hard for me to reference each piece, since it would have to be referenced to most of them

== MistaJacob, reviewer 3 ==

=== The feedback will be given in the form: ===
*My feedback
**My feedback

OR

*’’Copy of your text’’
**My feedback

=== Feedback ===
*The general formatting is almost as it’s supposed to be. The pictures though lack the numbering and the references in the text, and you shift with using ‘thumbs’ and placing it in the middle. Consistency can be recommended for a better visual overview.
'''Answer''': It is true. I have moved all of the pictures to the right and reduced their sizes to have a nicer layout.
*The language is clear and easy to read, only with small number of places where i found typo’s, like in “Limitation” where you start and end a sentence with: Therefore
**I will not comment these since they will be obvious to you when you read through your article for corrections.
'''Answer''': Corrected

*I found the article relevant, with a good red thread through it.
*The step by step approach worked as it should. That being said, the reader’s understanding could have been improved if you included a practical example you carried out through all steps
**As you promised in the introduction :)
'''Answer''': TO DO
*in the section “Key Concepts”, the sequence of the bullet point list should be the same as the sequence in which they are explained, or vice versa.
*’’The process of making a PERT analysis can be divided into 4 steps:’’
**you have written 5 bullet points below
'''Answer''': Good eye ;)

*‘’Preparation of a list of all the tasks that will be involved in a given project’’
**I would stick to using ‘activities’ and not ‘tasks’ as you write here.
'''Answer''': True, especially that activties is a word that I have put in the key concepts

**There are other places (maybe only one) where you use task as well
'''Answer''': changed it everywhere

*I would suggest that you also explain the term ‘float’, since it appears in your figure
'''Answer''': I was going to explain the box a bit more.

*‘’In this step we estimate the amount of time that can be taken by each activity.’’
**You normally don’t use ‘we’
'''Answer''': My bad.

*‘’A project cannot be completed as long as his longest component isn't finished.’’
**Don’t know whether you would be able to argue your way out of defining a project as being ‘male’ ;)
*‘’Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project.’’
**Double up
'''Answer''': Corrected.
*Since you describe the other tool in the comparison very briefly, I would suggest to include links to their respective articles (if they exists)
'''Answer''': Done

Program evaluation and review technique (PERT)

2015-09-28T17:31:44Z

S141938: /* See also */

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects, its advantages and limitations.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

The '''activities''' are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The '''events''' are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

A '''network diagram''' is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The '''critical path''' is the sequence of activities which add up to the longest overall duration. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 5 steps:
* Preparation of a list of all the activities that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

[[File:PERT box.png | thumb | right | 300px | '''Figure 1''': PERT box ]]

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation showed in figure 1. This box will later be filled with other time informations about the project. For instance the earliest start time, which is self-explanatory, is the time when the earliest date for an activity to be started. This goes in pair with the earliest finish - earliest date when the activity can be finished. These two timings report the most optimistic scenario and aren't usually met. The same logic applies to the latest times, but those are considered as the pessimistic time. More about these times will be later. Float is basically the difference between the earliest times and the latest. Its purpose is too give an overview of the timing margin that a certain activity has.

=== Network diagram ===

[[File:PERT network.png | thumb | right | 300px | '''Figure 2''': PERT network with critical path ]]

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the activity and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes just like on figure 2. For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

=== Estimation of the time ===

In this step, the amount of time that can be taken by each activity is estimated. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as its longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the activities which have a null difference between the respective times. Those activities constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between activities
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager.
* No representation of repetitive activities. Because the project is presented in a network form, a repetitive activity would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:PERT network in ms Project.png | thumb | right | 300px | '''Figure 3''': PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project (see figure 3) or Oracle Primavera. PERT charts are used to visualize the dependencies between different activities. To see the timing and progress of the project another similar tool is widely used, the [[ The Gantt chart and the usage nowadays | Gantt charts ]]. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 300px | '''Figure 4''': Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the [[ The Critical Path Method (CPM) | Critical Path Analysis ]], the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization. In the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities and progress of the project (see figure 4). Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

'''Design Structure Matrix''' (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization. DSM matrices represent basically the same information as a PERT network, which is different activities and their connections. The advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network (see figure 5). However it doesn't give any information concerning timings of activities. It is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | right | 300px | '''Figure 5''': DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== See also ==

* [[ Responsibility Assignment Matrix (RACI Matrix) ]]
* [[ Scheduling techniques in Project Management ]]
* [[ Critical chain project management (CCPM) ]]
* [[ Critical Path Method in Construction Industry ]]
* [[ Critical Chain Project Management ]]
* [[ Metra Potential Method ]]
* [[ The Critical Path Method (CPM) ]]

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
* Project Management Demystified: Today's Tools and Techniques, Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.

Program evaluation and review technique (PERT)

2015-09-28T17:30:40Z

S141938:

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects, its advantages and limitations.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

The '''activities''' are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The '''events''' are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

A '''network diagram''' is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The '''critical path''' is the sequence of activities which add up to the longest overall duration. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 5 steps:
* Preparation of a list of all the activities that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

[[File:PERT box.png | thumb | right | 300px | '''Figure 1''': PERT box ]]

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation showed in figure 1. This box will later be filled with other time informations about the project. For instance the earliest start time, which is self-explanatory, is the time when the earliest date for an activity to be started. This goes in pair with the earliest finish - earliest date when the activity can be finished. These two timings report the most optimistic scenario and aren't usually met. The same logic applies to the latest times, but those are considered as the pessimistic time. More about these times will be later. Float is basically the difference between the earliest times and the latest. Its purpose is too give an overview of the timing margin that a certain activity has.

=== Network diagram ===

[[File:PERT network.png | thumb | right | 300px | '''Figure 2''': PERT network with critical path ]]

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the activity and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes just like on figure 2. For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

=== Estimation of the time ===

In this step, the amount of time that can be taken by each activity is estimated. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as its longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the activities which have a null difference between the respective times. Those activities constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between activities
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager.
* No representation of repetitive activities. Because the project is presented in a network form, a repetitive activity would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:PERT network in ms Project.png | thumb | right | 300px | '''Figure 3''': PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project (see figure 3) or Oracle Primavera. PERT charts are used to visualize the dependencies between different activities. To see the timing and progress of the project another similar tool is widely used, the [[ The Gantt chart and the usage nowadays | Gantt charts ]]. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 300px | '''Figure 4''': Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the [[ The Critical Path Method (CPM) | Critical Path Analysis ]], the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization. In the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities and progress of the project (see figure 4). Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

'''Design Structure Matrix''' (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization. DSM matrices represent basically the same information as a PERT network, which is different activities and their connections. The advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network (see figure 5). However it doesn't give any information concerning timings of activities. It is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | right | 300px | '''Figure 5''': DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== See also ==

* [[ Responsibility Assignment Matrix (RACI Matrix) ]]
* [[ Scheduling techniques in Project Management ]]
* [[ Critical chain project management (CCPM) ]]
* [[ Critical Path Method in Construction Industry ]]
* [[ Critical Chain Project Management ]]

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
* Project Management Demystified: Today's Tools and Techniques, Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.

Program evaluation and review technique (PERT)

2015-09-28T16:59:05Z

S141938:

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects, its advantages and limitations.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

The '''activities''' are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The '''events''' are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

A '''network diagram''' is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The '''critical path''' is the sequence of activities which add up to the longest overall duration. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 5 steps:
* Preparation of a list of all the activities that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

[[File:PERT box.png | thumb | right | 300px | '''Figure 1''': PERT box ]]

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation showed in figure 1. This box will later be filled with other time informations about the project. For instance the earliest start time, which is self-explanatory, is the time when the earliest date for an activity to be started. This goes in pair with the earliest finish - earliest date when the activity can be finished. These two timings report the most optimistic scenario and aren't usually met. The same logic applies to the latest times, but those are considered as the pessimistic time. More about these times will be later. Float is basically the difference between the earliest times and the latest. Its purpose is too give an overview of the timing margin that a certain activity has.

=== Network diagram ===

[[File:PERT network.png | thumb | right | 300px | '''Figure 2''': PERT network with critical path ]]

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the activity and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes just like on figure 2. For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

=== Estimation of the time ===

In this step, the amount of time that can be taken by each activity is estimated. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as its longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the activities which have a null difference between the respective times. Those activities constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between activities
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager.
* No representation of repetitive activities. Because the project is presented in a network form, a repetitive activity would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:PERT network in ms Project.png | thumb | right | 300px | '''Figure 3''': PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project (see figure 3) or Oracle Primavera. PERT charts are used to visualize the dependencies between different activities. To see the timing and progress of the project another similar tool is widely used, the [[ The Gantt chart and the usage nowadays | Gantt charts ]]. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 300px | '''Figure 4''': Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the [[ The Critical Path Method (CPM) | Critical Path Analysis ]], the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization. In the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities and progress of the project (see figure 4). Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

'''Design Structure Matrix''' (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization. DSM matrices represent basically the same information as a PERT network, which is different activities and their connections. The advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network (see figure 5). However it doesn't give any information concerning timings of activities. It is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | right | 300px | '''Figure 5''': DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== See also ==

[[ Responsibility Assignment Matrix (RACI Matrix) | Responsibility Assignment Matrix (RAM) ]]

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
* Project Management Demystified: Today's Tools and Techniques, Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.

Program evaluation and review technique (PERT)

2015-09-28T16:41:29Z

S141938: /* Comparison to other tools */

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects, its advantages and limitations.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

The '''activities''' are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The '''events''' are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

A '''network diagram''' is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The '''critical path''' is the sequence of activities which add up to the longest overall duration. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 5 steps:
* Preparation of a list of all the activities that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

[[File:PERT box.png | thumb | right | 300px | '''Figure 1''': PERT box ]]

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation showed in figure 1. This box will later be filled with other time informations about the project. For instance the earliest start time, which is self-explanatory, is the time when the earliest date for an activity to be started. This goes in pair with the earliest finish - earliest date when the activity can be finished. These two timings report the most optimistic scenario and aren't usually met. The same logic applies to the latest times, but those are considered as the pessimistic time. More about these times will be later. Float is basically the difference between the earliest times and the latest. Its purpose is too give an overview of the timing margin that a certain activity has.

=== Network diagram ===

[[File:PERT network.png | thumb | right | 300px | '''Figure 2''': PERT network with critical path ]]

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the activity and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes just like on figure 2. For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

=== Estimation of the time ===

In this step, the amount of time that can be taken by each activity is estimated. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as its longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the activities which have a null difference between the respective times. Those activities constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between activities
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager.
* No representation of repetitive activities. Because the project is presented in a network form, a repetitive activity would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:PERT network in ms Project.png | thumb | right | 300px | '''Figure 3''': PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project (see figure 3) or Oracle Primavera. PERT charts are used to visualize the dependencies between different activities. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 300px | '''Figure 4''': Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization. In the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities and progress of the project (see figure 4). Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization. DSM matrices represent basically the same information as a PERT network, which is different activities and their connections. The advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network (see figure 5). However it doesn't give any information concerning timings of activities. It is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | right | 300px | '''Figure 5''': DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
* Project Management Demystified: Today's Tools and Techniques, Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.

Program evaluation and review technique (PERT)

2015-09-28T16:34:58Z

S141938: /* Critical path estimation */

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects, its advantages and limitations.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

The '''activities''' are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The '''events''' are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

A '''network diagram''' is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The '''critical path''' is the sequence of activities which add up to the longest overall duration. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 5 steps:
* Preparation of a list of all the activities that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

[[File:PERT box.png | thumb | right | 300px | '''Figure 1''': PERT box ]]

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation showed in figure 1. This box will later be filled with other time informations about the project. For instance the earliest start time, which is self-explanatory, is the time when the earliest date for an activity to be started. This goes in pair with the earliest finish - earliest date when the activity can be finished. These two timings report the most optimistic scenario and aren't usually met. The same logic applies to the latest times, but those are considered as the pessimistic time. More about these times will be later. Float is basically the difference between the earliest times and the latest. Its purpose is too give an overview of the timing margin that a certain activity has.

=== Network diagram ===

[[File:PERT network.png | thumb | right | 300px | '''Figure 2''': PERT network with critical path ]]

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the activity and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes just like on figure 2. For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

=== Estimation of the time ===

In this step, the amount of time that can be taken by each activity is estimated. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as its longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the activities which have a null difference between the respective times. Those activities constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between activities
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager.
* No representation of repetitive activities. Because the project is presented in a network form, a repetitive activity would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:PERT network in ms Project.png | thumb | right | 300px | '''Figure 3''': PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project (see figure 3) or Oracle Primavera. PERT charts are used to visualize the dependencies between different activities. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 300px | '''Figure 4''': Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization. In the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project (see figure 4). Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization. DSM matrices represent basically the same information as a PERT network, which is different activities and their connections. The advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network (see figure 5). However it doesn't give any information concerning timings of activities. It is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | right | 300px | '''Figure 5''': DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
* Project Management Demystified: Today's Tools and Techniques, Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.

Program evaluation and review technique (PERT)

2015-09-28T16:34:16Z

S141938: /* Estimation of the time */

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects, its advantages and limitations.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

The '''activities''' are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The '''events''' are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

A '''network diagram''' is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The '''critical path''' is the sequence of activities which add up to the longest overall duration. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 5 steps:
* Preparation of a list of all the activities that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

[[File:PERT box.png | thumb | right | 300px | '''Figure 1''': PERT box ]]

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation showed in figure 1. This box will later be filled with other time informations about the project. For instance the earliest start time, which is self-explanatory, is the time when the earliest date for an activity to be started. This goes in pair with the earliest finish - earliest date when the activity can be finished. These two timings report the most optimistic scenario and aren't usually met. The same logic applies to the latest times, but those are considered as the pessimistic time. More about these times will be later. Float is basically the difference between the earliest times and the latest. Its purpose is too give an overview of the timing margin that a certain activity has.

=== Network diagram ===

[[File:PERT network.png | thumb | right | 300px | '''Figure 2''': PERT network with critical path ]]

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the activity and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes just like on figure 2. For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

=== Estimation of the time ===

In this step, the amount of time that can be taken by each activity is estimated. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as his longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the activities which have a null difference between the respective times. Those activities constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between activities
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager.
* No representation of repetitive activities. Because the project is presented in a network form, a repetitive activity would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:PERT network in ms Project.png | thumb | right | 300px | '''Figure 3''': PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project (see figure 3) or Oracle Primavera. PERT charts are used to visualize the dependencies between different activities. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 300px | '''Figure 4''': Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization. In the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project (see figure 4). Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization. DSM matrices represent basically the same information as a PERT network, which is different activities and their connections. The advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network (see figure 5). However it doesn't give any information concerning timings of activities. It is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | right | 300px | '''Figure 5''': DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
* Project Management Demystified: Today's Tools and Techniques, Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.

Talk:Program evaluation and review technique (PERT)

2015-09-28T16:31:22Z

S141938:

Anna: Very nice topic! It seems that you have a good grasp on the structure of the article and the theme fits the first article type: method :).

== Reviewer 1 - Biankajuh: Feedback==
# I have find your abstract very well-designed which fulfill the role of introducing the main purpose and highlights of the article. Also commendable that you mention the limitation of the PERT model and talk about the comparative tools as well as the modifications.
'''Answer''' : Extendended the last sentence a bit.
# The article is nicely illustrated with the pictures which help the understanding. Although, I would suggest to name them as ‘’Figure 1, 2, 3, …etc.’’ which would allow to refer to the pictures more specifically. So for example instead of the sentence “This information is presented in a box representation.”, you could say “This information is presented in the box representation showed in Figure 1.”.
'''Answer''': Added the figure numbering and some references in the text to the figures.
#The third figure entitled in “PERT network in MS Project 2013” is quite unclear. Could you increase the quality of the picture?
'''Answer''': Changed it (that's the best I can get)
#In some cases, too long sentences could be substituted by two or three shorter ones to help the understanding. For example: “The essential difference between a PERT chart and DSM is the visualization; DSM matrices represent basically the same information as a PERT network, which is different activities and their connections; the advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network.” (Comparison to other tools) —> Could be changed to: “The essential difference between a PERT chart and DSM is the visualization. DSM matrices represent basically the same information as a PERT network, which is different activities and their connections. The advantage of this representation in DSM is its conciseness compared to PERT, where lots of space is required to have a readable network.”
'''Answer''': I have made a few changes, wherever I could.
#Grammatical/Formatting hints:
##Space missing between two sentence: “whereas the events are the nodes.For instance,” (Network diagram),
'''Answer''': Added
##No need for space before question mark: “How do they differ from eachother ?” (Comparison to other tools)
'''Answer''': Changed it, but did'nt know it was an 'error'
#Regarding the Bibliography, I would note to refer all these references within the text of the article at the corresponding spaces.

'''Reviewer 2 – User: s113735'''
Feedback: Program evaluation and review technique (PERT)
Formal Aspects:
*The article clearly follows the “method or tool” structure required. Super!
*The grammar and spelling in the article is at a decently high level. The sentences are short and concise, which makes it a pleasurably read with clear and easy to understand points.
'''Answer''': Thanks ;)
*Your choice of figures are good and in line with the points, you are trying to make. Some figures could, however, be explained a little better (for instance the PERT box).
'''Answer''': I have explained everything that is contained in the PERT box
*Figures are missing references.
'''Answer''': Applied changes
*The article has a bibliography, but is otherwise free of references and links. This makes it really hardto check the validity of your points. The article will have to be referenced.

Content Aspects:
*The article is clearly within the scope as it relates directly to a “Program” tool/method.
*The length of the article seems fair, but a few headings and sub-sections could easily be elaborated a bit. (For instance the “process” section: What are the benefits/drawbacks from using the tools you present? Are the tools prescribed or optional? Etc… You explain the overall applications and limitations for the PERT model, but not for the individual tools).
*The “critical path” in Project Management to my knowledge is not “the path that includes the most time consuming tasks” but is instead “the sequence of activities which add up to the longest overall duration”. You clearly show in your article that you know this while ALSO showing you know how to calculate the critical path.
'''Answer''': Applied your suggestion. Thanks ;)
*With a little bit sharper terminology and definitions, it would increase the understanding a lot.
*When making a statement like: “But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures.” This definitely need to be referenced.
Other than in a few cases the article is generally void of personal/unverifiable opinions, which is good.
*So far, the article doesn’t link to any other articles on the Wiki. I understand that it might be tough to find something directly related to this specific tool amongst the rather limited topics on the Wiki. I suggest trying to find some broad topics or even Categories to link to when writing. For instance, you might link to “human behaviour” (a category on the Wiki) when writing about the “agreement dimension” in the Stacey Matrix.

Overall Conclusion: The article is written at a high level and is easy to read and understand. Some points could however be elaborated a bit and the article needs to be referenced according to Wiki standards using the
<nowiki><ref> lastname, firstname (year) [www.link.com “linkname”] </ref></nowiki> standard.

== MistaJacob, reviewer 3 ==

=== The feedback will be given in the form: ===
*My feedback
**My feedback

OR

*’’Copy of your text’’
**My feedback

=== Feedback ===
*The general formatting is almost as it’s supposed to be. The pictures though lack the numbering and the references in the text, and you shift with using ‘thumbs’ and placing it in the middle. Consistency can be recommended for a better visual overview.
'''Answer''': It is true. I have moved all of the pictures to the right and reduced their sizes to have a nicer layout.
*The language is clear and easy to read, only with small number of places where i found typo’s, like in “Limitation” where you start and end a sentence with: Therefore
**I will not comment these since they will be obvious to you when you read through your article for corrections.
'''Answer''': Corrected

*I found the article relevant, with a good red thread through it.
*The step by step approach worked as it should. That being said, the reader’s understanding could have been improved if you included a practical example you carried out through all steps
**As you promised in the introduction :)
'''Answer''': TO DO
*in the section “Key Concepts”, the sequence of the bullet point list should be the same as the sequence in which they are explained, or vice versa.
*’’The process of making a PERT analysis can be divided into 4 steps:’’
**you have written 5 bullet points below
'''Answer''': Good eye ;)

*‘’Preparation of a list of all the tasks that will be involved in a given project’’
**I would stick to using ‘activities’ and not ‘tasks’ as you write here.
'''Answer''': True, especially that activties is a word that I have put in the key concepts
**There are other places (maybe only one) where you use task as well
*I would suggest that you also explain the term ‘float’, since it appears in your figure
*‘’In this step we estimate the amount of time that can be taken by each activity.’’
**You normally don’t use ‘we’
*‘’A project cannot be completed as long as his longest component isn't finished.’’
**Don’t know whether you would be able to argue your way out of defining a project as being ‘male’ ;)
*‘’Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project.’’
**Double up
*Since you describe the other tool in the comparison very briefly, I would suggest to include links to their respective articles (if they exists)

Program evaluation and review technique (PERT)

2015-09-28T16:30:40Z

S141938: /* Applications and limitations */

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects, its advantages and limitations.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

The '''activities''' are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The '''events''' are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

A '''network diagram''' is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The '''critical path''' is the sequence of activities which add up to the longest overall duration. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 5 steps:
* Preparation of a list of all the activities that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

[[File:PERT box.png | thumb | right | 300px | '''Figure 1''': PERT box ]]

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation showed in figure 1. This box will later be filled with other time informations about the project. For instance the earliest start time, which is self-explanatory, is the time when the earliest date for an activity to be started. This goes in pair with the earliest finish - earliest date when the activity can be finished. These two timings report the most optimistic scenario and aren't usually met. The same logic applies to the latest times, but those are considered as the pessimistic time. More about these times will be later. Float is basically the difference between the earliest times and the latest. Its purpose is too give an overview of the timing margin that a certain activity has.

=== Network diagram ===

[[File:PERT network.png | thumb | right | 300px | '''Figure 2''': PERT network with critical path ]]

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the activity and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes just like on figure 2. For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

=== Estimation of the time ===

In this step we estimate the amount of time that can be taken by each activity. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as his longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the activities which have a null difference between the respective times. Those activities constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between activities
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager.
* No representation of repetitive activities. Because the project is presented in a network form, a repetitive activity would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:PERT network in ms Project.png | thumb | right | 300px | '''Figure 3''': PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project (see figure 3) or Oracle Primavera. PERT charts are used to visualize the dependencies between different activities. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 300px | '''Figure 4''': Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization. In the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project (see figure 4). Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization. DSM matrices represent basically the same information as a PERT network, which is different activities and their connections. The advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network (see figure 5). However it doesn't give any information concerning timings of activities. It is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | right | 300px | '''Figure 5''': DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
* Project Management Demystified: Today's Tools and Techniques, Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.

Program evaluation and review technique (PERT)

2015-09-28T16:29:32Z

S141938: /* Critical path estimation */

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects, its advantages and limitations.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

The '''activities''' are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The '''events''' are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

A '''network diagram''' is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The '''critical path''' is the sequence of activities which add up to the longest overall duration. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 5 steps:
* Preparation of a list of all the activities that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

[[File:PERT box.png | thumb | right | 300px | '''Figure 1''': PERT box ]]

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation showed in figure 1. This box will later be filled with other time informations about the project. For instance the earliest start time, which is self-explanatory, is the time when the earliest date for an activity to be started. This goes in pair with the earliest finish - earliest date when the activity can be finished. These two timings report the most optimistic scenario and aren't usually met. The same logic applies to the latest times, but those are considered as the pessimistic time. More about these times will be later. Float is basically the difference between the earliest times and the latest. Its purpose is too give an overview of the timing margin that a certain activity has.

=== Network diagram ===

[[File:PERT network.png | thumb | right | 300px | '''Figure 2''': PERT network with critical path ]]

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the activity and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes just like on figure 2. For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

=== Estimation of the time ===

In this step we estimate the amount of time that can be taken by each activity. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as his longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the activities which have a null difference between the respective times. Those activities constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between tasks
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager.
* No representation of repetitive tasks. Because the project is presented in a network form, a repetitive task would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:PERT network in ms Project.png | thumb | right | 300px | '''Figure 3''': PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project (see figure 3) or Oracle Primavera. PERT charts are used to visualize the dependencies between different tasks. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 300px | '''Figure 4''': Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization. In the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project (see figure 4). Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization. DSM matrices represent basically the same information as a PERT network, which is different activities and their connections. The advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network (see figure 5). However it doesn't give any information concerning timings of activities. It is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | right | 300px | '''Figure 5''': DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
* Project Management Demystified: Today's Tools and Techniques, Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.

Program evaluation and review technique (PERT)

2015-09-28T16:29:00Z

S141938: /* The process */

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects, its advantages and limitations.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

The '''activities''' are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The '''events''' are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

A '''network diagram''' is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The '''critical path''' is the sequence of activities which add up to the longest overall duration. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 5 steps:
* Preparation of a list of all the activities that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

[[File:PERT box.png | thumb | right | 300px | '''Figure 1''': PERT box ]]

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation showed in figure 1. This box will later be filled with other time informations about the project. For instance the earliest start time, which is self-explanatory, is the time when the earliest date for an activity to be started. This goes in pair with the earliest finish - earliest date when the activity can be finished. These two timings report the most optimistic scenario and aren't usually met. The same logic applies to the latest times, but those are considered as the pessimistic time. More about these times will be later. Float is basically the difference between the earliest times and the latest. Its purpose is too give an overview of the timing margin that a certain activity has.

=== Network diagram ===

[[File:PERT network.png | thumb | right | 300px | '''Figure 2''': PERT network with critical path ]]

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the activity and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes just like on figure 2. For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

=== Estimation of the time ===

In this step we estimate the amount of time that can be taken by each activity. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as his longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the tasks which have a null difference between the respective times. Those tasks constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between tasks
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager.
* No representation of repetitive tasks. Because the project is presented in a network form, a repetitive task would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:PERT network in ms Project.png | thumb | right | 300px | '''Figure 3''': PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project (see figure 3) or Oracle Primavera. PERT charts are used to visualize the dependencies between different tasks. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 300px | '''Figure 4''': Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization. In the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project (see figure 4). Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization. DSM matrices represent basically the same information as a PERT network, which is different activities and their connections. The advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network (see figure 5). However it doesn't give any information concerning timings of activities. It is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | right | 300px | '''Figure 5''': DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
* Project Management Demystified: Today's Tools and Techniques, Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.

Program evaluation and review technique (PERT)

2015-09-28T16:28:35Z

S141938: /* Network diagram */

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects, its advantages and limitations.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

The '''activities''' are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The '''events''' are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

A '''network diagram''' is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The '''critical path''' is the sequence of activities which add up to the longest overall duration. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 5 steps:
* Preparation of a list of all the tasks that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

[[File:PERT box.png | thumb | right | 300px | '''Figure 1''': PERT box ]]

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation showed in figure 1. This box will later be filled with other time informations about the project. For instance the earliest start time, which is self-explanatory, is the time when the earliest date for an activity to be started. This goes in pair with the earliest finish - earliest date when the activity can be finished. These two timings report the most optimistic scenario and aren't usually met. The same logic applies to the latest times, but those are considered as the pessimistic time. More about these times will be later. Float is basically the difference between the earliest times and the latest. Its purpose is too give an overview of the timing margin that a certain activity has.

=== Network diagram ===

[[File:PERT network.png | thumb | right | 300px | '''Figure 2''': PERT network with critical path ]]

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the activity and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes just like on figure 2. For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

=== Estimation of the time ===

In this step we estimate the amount of time that can be taken by each activity. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as his longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the tasks which have a null difference between the respective times. Those tasks constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between tasks
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager.
* No representation of repetitive tasks. Because the project is presented in a network form, a repetitive task would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:PERT network in ms Project.png | thumb | right | 300px | '''Figure 3''': PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project (see figure 3) or Oracle Primavera. PERT charts are used to visualize the dependencies between different tasks. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 300px | '''Figure 4''': Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization. In the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project (see figure 4). Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization. DSM matrices represent basically the same information as a PERT network, which is different activities and their connections. The advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network (see figure 5). However it doesn't give any information concerning timings of activities. It is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | right | 300px | '''Figure 5''': DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
* Project Management Demystified: Today's Tools and Techniques, Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.

Program evaluation and review technique (PERT)

2015-09-28T16:27:22Z

S141938: /* The process */

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects, its advantages and limitations.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

The '''activities''' are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The '''events''' are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

A '''network diagram''' is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The '''critical path''' is the sequence of activities which add up to the longest overall duration. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 5 steps:
* Preparation of a list of all the tasks that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

[[File:PERT box.png | thumb | right | 300px | '''Figure 1''': PERT box ]]

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation showed in figure 1. This box will later be filled with other time informations about the project. For instance the earliest start time, which is self-explanatory, is the time when the earliest date for an activity to be started. This goes in pair with the earliest finish - earliest date when the activity can be finished. These two timings report the most optimistic scenario and aren't usually met. The same logic applies to the latest times, but those are considered as the pessimistic time. More about these times will be later. Float is basically the difference between the earliest times and the latest. Its purpose is too give an overview of the timing margin that a certain activity has.

=== Network diagram ===

[[File:PERT network.png | thumb | right | 300px | '''Figure 2''': PERT network with critical path ]]

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the task and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes just like on figure 2. For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

=== Estimation of the time ===

In this step we estimate the amount of time that can be taken by each activity. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as his longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the tasks which have a null difference between the respective times. Those tasks constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between tasks
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager.
* No representation of repetitive tasks. Because the project is presented in a network form, a repetitive task would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:PERT network in ms Project.png | thumb | right | 300px | '''Figure 3''': PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project (see figure 3) or Oracle Primavera. PERT charts are used to visualize the dependencies between different tasks. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 300px | '''Figure 4''': Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization. In the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project (see figure 4). Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization. DSM matrices represent basically the same information as a PERT network, which is different activities and their connections. The advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network (see figure 5). However it doesn't give any information concerning timings of activities. It is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | right | 300px | '''Figure 5''': DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
* Project Management Demystified: Today's Tools and Techniques, Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.

Program evaluation and review technique (PERT)

2015-09-28T16:26:21Z

S141938: /* Limitations */

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects, its advantages and limitations.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

The '''activities''' are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The '''events''' are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

A '''network diagram''' is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The '''critical path''' is the sequence of activities which add up to the longest overall duration. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 4 steps:
* Preparation of a list of all the tasks that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

[[File:PERT box.png | thumb | right | 300px | '''Figure 1''': PERT box ]]

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation showed in figure 1. This box will later be filled with other time informations about the project. For instance the earliest start time, which is self-explanatory, is the time when the earliest date for an activity to be started. This goes in pair with the earliest finish - earliest date when the activity can be finished. These two timings report the most optimistic scenario and aren't usually met. The same logic applies to the latest times, but those are considered as the pessimistic time. More about these times will be later. Float is basically the difference between the earliest times and the latest. Its purpose is too give an overview of the timing margin that a certain activity has.

=== Network diagram ===

[[File:PERT network.png | thumb | right | 300px | '''Figure 2''': PERT network with critical path ]]

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the task and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes just like on figure 2. For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

=== Estimation of the time ===

In this step we estimate the amount of time that can be taken by each activity. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as his longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the tasks which have a null difference between the respective times. Those tasks constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between tasks
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager.
* No representation of repetitive tasks. Because the project is presented in a network form, a repetitive task would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:PERT network in ms Project.png | thumb | right | 300px | '''Figure 3''': PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project (see figure 3) or Oracle Primavera. PERT charts are used to visualize the dependencies between different tasks. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 300px | '''Figure 4''': Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization. In the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project (see figure 4). Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization. DSM matrices represent basically the same information as a PERT network, which is different activities and their connections. The advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network (see figure 5). However it doesn't give any information concerning timings of activities. It is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | right | 300px | '''Figure 5''': DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
* Project Management Demystified: Today's Tools and Techniques, Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.

Program evaluation and review technique (PERT)

2015-09-28T16:22:13Z

S141938:

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects, its advantages and limitations.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

The '''activities''' are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The '''events''' are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

A '''network diagram''' is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The '''critical path''' is the sequence of activities which add up to the longest overall duration. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 4 steps:
* Preparation of a list of all the tasks that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

[[File:PERT box.png | thumb | right | 300px | '''Figure 1''': PERT box ]]

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation showed in figure 1. This box will later be filled with other time informations about the project. For instance the earliest start time, which is self-explanatory, is the time when the earliest date for an activity to be started. This goes in pair with the earliest finish - earliest date when the activity can be finished. These two timings report the most optimistic scenario and aren't usually met. The same logic applies to the latest times, but those are considered as the pessimistic time. More about these times will be later. Float is basically the difference between the earliest times and the latest. Its purpose is too give an overview of the timing margin that a certain activity has.

=== Network diagram ===

[[File:PERT network.png | thumb | right | 300px | '''Figure 2''': PERT network with critical path ]]

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the task and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes just like on figure 2. For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

=== Estimation of the time ===

In this step we estimate the amount of time that can be taken by each activity. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as his longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the tasks which have a null difference between the respective times. Those tasks constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between tasks
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager. Therefore
* No representation of repetitive tasks. Because the project is presented in a network form, a repetitive task would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:PERT network in ms Project.png | thumb | right | 300px | '''Figure 3''': PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project (see figure 3) or Oracle Primavera. PERT charts are used to visualize the dependencies between different tasks. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 300px | '''Figure 4''': Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization. In the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project (see figure 4). Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization. DSM matrices represent basically the same information as a PERT network, which is different activities and their connections. The advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network (see figure 5). However it doesn't give any information concerning timings of activities. It is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | right | 300px | '''Figure 5''': DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
* Project Management Demystified: Today's Tools and Techniques, Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.

Program evaluation and review technique (PERT)

2015-09-28T16:21:28Z

S141938:

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects, its advantages and limitations.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

The '''activities''' are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The '''events''' are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

A '''network diagram''' is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The '''critical path''' is the sequence of activities which add up to the longest overall duration. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 4 steps:
* Preparation of a list of all the tasks that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

[[File:PERT box.png | thumb | right | 300px | '''Figure 1''': PERT box ]]

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation showed in figure 1. This box will later be filled with other time informations about the project. For instance the earliest start time, which is self-explanatory, is the time when the earliest date for an activity to be started. This goes in pair with the earliest finish - earliest date when the activity can be finished. These two timings report the most optimistic scenario and aren't usually met. The same logic applies to the latest times, but those are considered as the pessimistic time. More about these times will be later. Float is basically the difference between the earliest times and the latest. Its purpose is too give an overview of the timing margin that a certain activity has.

=== Network diagram ===

[[File:PERT network.png | thumb | right | 300px | '''Figure 2''': PERT network with critical path ]]

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the task and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes just like on figure 2. For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

=== Estimation of the time ===

In this step we estimate the amount of time that can be taken by each activity. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as his longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the tasks which have a null difference between the respective times. Those tasks constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between tasks
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager. Therefore
* No representation of repetitive tasks. Because the project is presented in a network form, a repetitive task would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:PERT network in ms Project.png | thumb | right | 300px | '''Figure 3''': PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project (see figure 3) or Oracle Primavera. PERT charts are used to visualize the dependencies between different tasks. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 300px | '''Figure 4''': Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization. In the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project (see figure 4). Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization. DSM matrices represent basically the same information as a PERT network, which is different activities and their connections. The advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network (see figure 5). However it doesn't give any information concerning timings of activities. It is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | center | 300px | '''Figure 5''': DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
* Project Management Demystified: Today's Tools and Techniques, Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.

Program evaluation and review technique (PERT)

2015-09-28T16:17:51Z

S141938: /* Key concepts */

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects, its advantages and limitations.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

The '''activities''' are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The '''events''' are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

A '''network diagram''' is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The '''critical path''' is the sequence of activities which add up to the longest overall duration. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 4 steps:
* Preparation of a list of all the tasks that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation showed in figure 1. This box will later be filled with other time informations about the project. For instance the earliest start time, which is self-explanatory, is the time when the earliest date for an activity to be started. This goes in pair with the earliest finish - earliest date when the activity can be finished. These two timings report the most optimistic scenario and aren't usually met. The same logic applies to the latest times, but those are considered as the pessimistic time. More about these times will be later. Float is basically the difference between the earliest times and the latest. Its purpose is too give an overview of the timing margin that a certain activity has.

[[File:PERT box.png | thumb | center | 500px | '''Figure 1''': PERT box ]]

=== Network diagram ===

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the task and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes just like on figure 2. For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

[[File:PERT network.png | thumb | center | 400px | '''Figure 2''': PERT network with critical path ]]

=== Estimation of the time ===

In this step we estimate the amount of time that can be taken by each activity. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as his longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the tasks which have a null difference between the respective times. Those tasks constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between tasks
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager. Therefore
* No representation of repetitive tasks. Because the project is presented in a network form, a repetitive task would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:PERT network in ms Project.png | thumb | right | 400px | '''Figure 3''': PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project (see figure 3) or Oracle Primavera. PERT charts are used to visualize the dependencies between different tasks. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 400px | '''Figure 4''': Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization. In the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project (see figure 4). Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization. DSM matrices represent basically the same information as a PERT network, which is different activities and their connections. The advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network (see figure 5). However it doesn't give any information concerning timings of activities. It is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | center | 350px | '''Figure 5''': DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
* Project Management Demystified: Today's Tools and Techniques, Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.

Program evaluation and review technique (PERT)

2015-09-28T16:16:19Z

S141938: /* Preparation phase */

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects, its advantages and limitations.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

A network diagram is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The activities are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The events are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

The critical path is the sequence of activities which add up to the longest overall duration. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 4 steps:
* Preparation of a list of all the tasks that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation showed in figure 1. This box will later be filled with other time informations about the project. For instance the earliest start time, which is self-explanatory, is the time when the earliest date for an activity to be started. This goes in pair with the earliest finish - earliest date when the activity can be finished. These two timings report the most optimistic scenario and aren't usually met. The same logic applies to the latest times, but those are considered as the pessimistic time. More about these times will be later. Float is basically the difference between the earliest times and the latest. Its purpose is too give an overview of the timing margin that a certain activity has.

[[File:PERT box.png | thumb | center | 500px | '''Figure 1''': PERT box ]]

=== Network diagram ===

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the task and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes just like on figure 2. For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

[[File:PERT network.png | thumb | center | 400px | '''Figure 2''': PERT network with critical path ]]

=== Estimation of the time ===

In this step we estimate the amount of time that can be taken by each activity. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as his longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the tasks which have a null difference between the respective times. Those tasks constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between tasks
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager. Therefore
* No representation of repetitive tasks. Because the project is presented in a network form, a repetitive task would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:PERT network in ms Project.png | thumb | right | 400px | '''Figure 3''': PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project (see figure 3) or Oracle Primavera. PERT charts are used to visualize the dependencies between different tasks. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 400px | '''Figure 4''': Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization. In the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project (see figure 4). Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization. DSM matrices represent basically the same information as a PERT network, which is different activities and their connections. The advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network (see figure 5). However it doesn't give any information concerning timings of activities. It is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | center | 350px | '''Figure 5''': DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
* Project Management Demystified: Today's Tools and Techniques, Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.

Program evaluation and review technique (PERT)

2015-09-28T16:15:59Z

S141938: /* Preparation phase */

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects, its advantages and limitations.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

A network diagram is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The activities are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The events are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

The critical path is the sequence of activities which add up to the longest overall duration. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 4 steps:
* Preparation of a list of all the tasks that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation showed in figure 1. This box will later be filled with other time informations about the project. For instance the earliest start time, which is self-explanatory, is the time when the earliest date for an activity to be started. This goes in pair with the earliest finish, earliest date when the activity can be finished. These two timings report the most optimistic scenario and aren't usually met. The same logic applies to the latest times, but those are considered as the pessimistic time. More about these times will be later. Float is basically the difference between the earliest times and the latest. Its purpose is too give an overview of the timing margin that a certain activity has.

[[File:PERT box.png | thumb | center | 500px | '''Figure 1''': PERT box ]]

=== Network diagram ===

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the task and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes just like on figure 2. For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

[[File:PERT network.png | thumb | center | 400px | '''Figure 2''': PERT network with critical path ]]

=== Estimation of the time ===

In this step we estimate the amount of time that can be taken by each activity. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as his longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the tasks which have a null difference between the respective times. Those tasks constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between tasks
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager. Therefore
* No representation of repetitive tasks. Because the project is presented in a network form, a repetitive task would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:PERT network in ms Project.png | thumb | right | 400px | '''Figure 3''': PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project (see figure 3) or Oracle Primavera. PERT charts are used to visualize the dependencies between different tasks. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 400px | '''Figure 4''': Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization. In the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project (see figure 4). Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization. DSM matrices represent basically the same information as a PERT network, which is different activities and their connections. The advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network (see figure 5). However it doesn't give any information concerning timings of activities. It is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | center | 350px | '''Figure 5''': DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
* Project Management Demystified: Today's Tools and Techniques, Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.

Program evaluation and review technique (PERT)

2015-09-28T16:15:43Z

S141938: /* Preparation phase */

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects, its advantages and limitations.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

A network diagram is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The activities are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The events are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

The critical path is the sequence of activities which add up to the longest overall duration. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 4 steps:
* Preparation of a list of all the tasks that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation showed in figure 1. This box will later be filled with other time informations about the project. For instance the earliest start time, which is self-explanatory, the time when the earliest date for an activity to be started. This goes in pair with the earliest finish, earliest date when the activity can be finished. These two timings report the most optimistic scenario and aren't usually met. The same logic applies to the latest times, but those are considered as the pessimistic time. More about these times will be later. Float is basically the difference between the earliest times and the latest. Its purpose is too give an overview of the timing margin that a certain activity has.

[[File:PERT box.png | thumb | center | 500px | '''Figure 1''': PERT box ]]

=== Network diagram ===

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the task and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes just like on figure 2. For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

[[File:PERT network.png | thumb | center | 400px | '''Figure 2''': PERT network with critical path ]]

=== Estimation of the time ===

In this step we estimate the amount of time that can be taken by each activity. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as his longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the tasks which have a null difference between the respective times. Those tasks constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between tasks
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager. Therefore
* No representation of repetitive tasks. Because the project is presented in a network form, a repetitive task would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:PERT network in ms Project.png | thumb | right | 400px | '''Figure 3''': PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project (see figure 3) or Oracle Primavera. PERT charts are used to visualize the dependencies between different tasks. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 400px | '''Figure 4''': Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization. In the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project (see figure 4). Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization. DSM matrices represent basically the same information as a PERT network, which is different activities and their connections. The advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network (see figure 5). However it doesn't give any information concerning timings of activities. It is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | center | 350px | '''Figure 5''': DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
* Project Management Demystified: Today's Tools and Techniques, Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.

Talk:Program evaluation and review technique (PERT)

2015-09-27T21:21:06Z

S141938: /* Reviewer 1 - Biankajuh: Feedback */

Anna: Very nice topic! It seems that you have a good grasp on the structure of the article and the theme fits the first article type: method :).

== Reviewer 1 - Biankajuh: Feedback==
# I have find your abstract very well-designed which fulfill the role of introducing the main purpose and highlights of the article. Also commendable that you mention the limitation of the PERT model and talk about the comparative tools as well as the modifications.
'''Answer''' : Extendended the last sentence a bit.
# The article is nicely illustrated with the pictures which help the understanding. Although, I would suggest to name them as ‘’Figure 1, 2, 3, …etc.’’ which would allow to refer to the pictures more specifically. So for example instead of the sentence “This information is presented in a box representation.”, you could say “This information is presented in the box representation showed in Figure 1.”.
'''Answer''': Added the figure numbering and some references in the text to the figures.
#The third figure entitled in “PERT network in MS Project 2013” is quite unclear. Could you increase the quality of the picture?
'''Answer''': Changed it (that's the best I can get)
#In some cases, too long sentences could be substituted by two or three shorter ones to help the understanding. For example: “The essential difference between a PERT chart and DSM is the visualization; DSM matrices represent basically the same information as a PERT network, which is different activities and their connections; the advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network.” (Comparison to other tools) —> Could be changed to: “The essential difference between a PERT chart and DSM is the visualization. DSM matrices represent basically the same information as a PERT network, which is different activities and their connections. The advantage of this representation in DSM is its conciseness compared to PERT, where lots of space is required to have a readable network.”
'''Answer''': I have made a few changes, wherever I could.
#Grammatical/Formatting hints:
##Space missing between two sentence: “whereas the events are the nodes.For instance,” (Network diagram),
'''Answer''': Added
##No need for space before question mark: “How do they differ from eachother ?” (Comparison to other tools)
'''Answer''': Changed it, but did'nt know it was an 'error'
#Regarding the Bibliography, I would note to refer all these references within the text of the article at the corresponding spaces.

'''Reviewer 2 – User: s113735'''
Feedback: Program evaluation and review technique (PERT)
Formal Aspects:
*The article clearly follows the “method or tool” structure required. Super!
*The grammar and spelling in the article is at a decently high level. The sentences are short and concise, which makes it a pleasurably read with clear and easy to understand points.
'''Answer''': Thanks ;)
*Your choice of figures are good and in line with the points, you are trying to make. Some figures could, however, be explained a little better (for instance the PERT box).
'''Answer''': I have explained everything that is contained in the PERT box
*Figures are missing references.
'''Answer''': Applied changes
*The article has a bibliography, but is otherwise free of references and links. This makes it really hardto check the validity of your points. The article will have to be referenced.

Content Aspects:
*The article is clearly within the scope as it relates directly to a “Program” tool/method.
*The length of the article seems fair, but a few headings and sub-sections could easily be elaborated a bit. (For instance the “process” section: What are the benefits/drawbacks from using the tools you present? Are the tools prescribed or optional? Etc… You explain the overall applications and limitations for the PERT model, but not for the individual tools).
*The “critical path” in Project Management to my knowledge is not “the path that includes the most time consuming tasks” but is instead “the sequence of activities which add up to the longest overall duration”. You clearly show in your article that you know this while ALSO showing you know how to calculate the critical path.
'''Answer''': Applied your suggestion. Thanks ;)
With a little bit sharper terminology and definitions, it would increase the understanding a lot.
*When making a statement like: “But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures.” This definitely need to be referenced.
Other than in a few cases the article is generally void of personal/unverifiable opinions, which is good.
*So far, the article doesn’t link to any other articles on the Wiki. I understand that it might be tough to find something directly related to this specific tool amongst the rather limited topics on the Wiki. I suggest trying to find some broad topics or even Categories to link to when writing. For instance, you might link to “human behaviour” (a category on the Wiki) when writing about the “agreement dimension” in the Stacey Matrix.

Overall Conclusion: The article is written at a high level and is easy to read and understand. Some points could however be elaborated a bit and the article needs to be referenced according to Wiki standards using the
<nowiki><ref> lastname, firstname (year) [www.link.com “linkname”] </ref></nowiki> standard.

== MistaJacob, reviewer 3 ==

=== The feedback will be given in the form: ===
*My feedback
**My feedback

OR

*’’Copy of your text’’
**My feedback

=== Feedback ===
*The general formatting is almost as it’s supposed to be. The pictures though lack the numbering and the references in the text, and you shift with using ‘thumbs’ and placing it in the middle. Consistency can be recommended for a better visual overview.
*The language is clear and easy to read, only with small number of places where i found typo’s, like in “Limitation” where you start and end a sentence with: Therefore
**I will not comment these since they will be obvious to you when you read through your article for corrections.

*I found the article relevant, with a good red thread through it.
*The step by step approach worked as it should. That being said, the reader’s understanding could have been improved if you included a practical example you carried out through all steps
**As you promised in the introduction :)
*in the section “Key Concepts”, the sequence of the bullet point list should be the same as the sequence in which they are explained, or vice versa.
*’’The process of making a PERT analysis can be divided into 4 steps:’’
**you have written 5 bullet points below
*‘’Preparation of a list of all the tasks that will be involved in a given project’’
**I would stick to using ‘activities’ and not ‘tasks’ as you write here.
**There are other places (maybe only one) where you use task as well
*I would suggest that you also explain the term ‘float’, since it appears in your figure
*‘’In this step we estimate the amount of time that can be taken by each activity.’’
**You normally don’t use ‘we’
*‘’A project cannot be completed as long as his longest component isn't finished.’’
**Don’t know whether you would be able to argue your way out of defining a project as being ‘male’ ;)
*‘’Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project.’’
**Double up
*Since you describe the other tool in the comparison very briefly, I would suggest to include links to their respective articles (if they exists)

Program evaluation and review technique (PERT)

2015-09-27T20:50:14Z

S141938: /* Key concepts */

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects, its advantages and limitations.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

A network diagram is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The activities are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The events are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

The critical path is the sequence of activities which add up to the longest overall duration. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 4 steps:
* Preparation of a list of all the tasks that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation showed in figure 1. This box will later be filled with other time informations about the project.

[[File:PERT box.png | thumb | center | 500px | '''Figure 1''': PERT box ]]

=== Network diagram ===

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the task and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes just like on figure 2. For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

[[File:PERT network.png | thumb | center | 400px | '''Figure 2''': PERT network with critical path ]]

=== Estimation of the time ===

In this step we estimate the amount of time that can be taken by each activity. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as his longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the tasks which have a null difference between the respective times. Those tasks constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between tasks
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager. Therefore
* No representation of repetitive tasks. Because the project is presented in a network form, a repetitive task would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:PERT network in ms Project.png | thumb | right | 400px | '''Figure 3''': PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project (see figure 3) or Oracle Primavera. PERT charts are used to visualize the dependencies between different tasks. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 400px | '''Figure 4''': Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization. In the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project (see figure 4). Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization. DSM matrices represent basically the same information as a PERT network, which is different activities and their connections. The advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network (see figure 5). However it doesn't give any information concerning timings of activities. It is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | center | 350px | '''Figure 5''': DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
* Project Management Demystified: Today's Tools and Techniques, Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.

Talk:Program evaluation and review technique (PERT)

2015-09-27T20:19:08Z

S141938: /* Reviewer 1 - Biankajuh: Feedback */

Anna: Very nice topic! It seems that you have a good grasp on the structure of the article and the theme fits the first article type: method :).

== Reviewer 1 - Biankajuh: Feedback==
# I have find your abstract very well-designed which fulfill the role of introducing the main purpose and highlights of the article. Also commendable that you mention the limitation of the PERT model and talk about the comparative tools as well as the modifications.
'''Answer''' : Extendended the last sentence a bit.
# The article is nicely illustrated with the pictures which help the understanding. Although, I would suggest to name them as ‘’Figure 1, 2, 3, …etc.’’ which would allow to refer to the pictures more specifically. So for example instead of the sentence “This information is presented in a box representation.”, you could say “This information is presented in the box representation showed in Figure 1.”.
'''Answer''': Added the figure numbering and some references in the text to the figures.
#The third figure entitled in “PERT network in MS Project 2013” is quite unclear. Could you increase the quality of the picture?
'''Answer''': Changed it (that's the best I can get)
#In some cases, too long sentences could be substituted by two or three shorter ones to help the understanding. For example: “The essential difference between a PERT chart and DSM is the visualization; DSM matrices represent basically the same information as a PERT network, which is different activities and their connections; the advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network.” (Comparison to other tools) —> Could be changed to: “The essential difference between a PERT chart and DSM is the visualization. DSM matrices represent basically the same information as a PERT network, which is different activities and their connections. The advantage of this representation in DSM is its conciseness compared to PERT, where lots of space is required to have a readable network.”
'''Answer''': I have made a few changes, wherever I could.
#Grammatical/Formatting hints:
##Space missing between two sentence: “whereas the events are the nodes.For instance,” (Network diagram),
'''Answer''': Added
##No need for space before question mark: “How do they differ from eachother ?” (Comparison to other tools)
'''Answer''': Changed it, but did'nt know it was an 'error'
#Regarding the Bibliography, I would note to refer all these references within the text of the article at the corresponding spaces.

'''Reviewer 2 – User: s113735'''
Feedback: Program evaluation and review technique (PERT)
Formal Aspects:
*The article clearly follows the “method or tool” structure required. Super!
*The grammar and spelling in the article is at a decently high level. The sentences are short and concise, which makes it a pleasurably read with clear and easy to understand points.
*Your choice of figures are good and in line with the points, you are trying to make. Some figures could, however, be explained a little better (for instance the PERT box).
*Figures are missing references.
*The article has a bibliography, but is otherwise free of references and links. This makes it really hardto check the validity of your points. The article will have to be referenced.

Content Aspects:
*The article is clearly within the scope as it relates directly to a “Program” tool/method.
*The length of the article seems fair, but a few headings and sub-sections could easily be elaborated a bit. (For instance the “process” section: What are the benefits/drawbacks from using the tools you present? Are the tools prescribed or optional? Etc… You explain the overall applications and limitations for the PERT model, but not for the individual tools).
*The “critical path” in Project Management to my knowledge is not “the path that includes the most time consuming tasks” but is instead “the sequence of activities which add up to the longest overall duration”. You clearly show in your article that you know this while ALSO showing you know how to calculate the critical path.
With a little bit sharper terminology and definitions, it would increase the understanding a lot.
*When making a statement like: “But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures.” This definitely need to be referenced.
Other than in a few cases the article is generally void of personal/unverifiable opinions, which is good.
*So far, the article doesn’t link to any other articles on the Wiki. I understand that it might be tough to find something directly related to this specific tool amongst the rather limited topics on the Wiki. I suggest trying to find some broad topics or even Categories to link to when writing. For instance, you might link to “human behaviour” (a category on the Wiki) when writing about the “agreement dimension” in the Stacey Matrix.

Overall Conclusion: The article is written at a high level and is easy to read and understand. Some points could however be elaborated a bit and the article needs to be referenced according to Wiki standards using the
<nowiki><ref> lastname, firstname (year) [www.link.com “linkname”] </ref></nowiki> standard.

== MistaJacob, reviewer 3 ==

=== The feedback will be given in the form: ===
*My feedback
**My feedback

OR

*’’Copy of your text’’
**My feedback

=== Feedback ===
*The general formatting is almost as it’s supposed to be. The pictures though lack the numbering and the references in the text, and you shift with using ‘thumbs’ and placing it in the middle. Consistency can be recommended for a better visual overview.
*The language is clear and easy to read, only with small number of places where i found typo’s, like in “Limitation” where you start and end a sentence with: Therefore
**I will not comment these since they will be obvious to you when you read through your article for corrections.

*I found the article relevant, with a good red thread through it.
*The step by step approach worked as it should. That being said, the reader’s understanding could have been improved if you included a practical example you carried out through all steps
**As you promised in the introduction :)
*in the section “Key Concepts”, the sequence of the bullet point list should be the same as the sequence in which they are explained, or vice versa.
*’’The process of making a PERT analysis can be divided into 4 steps:’’
**you have written 5 bullet points below
*‘’Preparation of a list of all the tasks that will be involved in a given project’’
**I would stick to using ‘activities’ and not ‘tasks’ as you write here.
**There are other places (maybe only one) where you use task as well
*I would suggest that you also explain the term ‘float’, since it appears in your figure
*‘’In this step we estimate the amount of time that can be taken by each activity.’’
**You normally don’t use ‘we’
*‘’A project cannot be completed as long as his longest component isn't finished.’’
**Don’t know whether you would be able to argue your way out of defining a project as being ‘male’ ;)
*‘’Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project.’’
**Double up
*Since you describe the other tool in the comparison very briefly, I would suggest to include links to their respective articles (if they exists)

Program evaluation and review technique (PERT)

2015-09-27T20:18:30Z

S141938: /* Comparison to other tools */

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects, its advantages and limitations.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

A network diagram is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The activities are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The events are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

The critical path is the path through the network that includes the most time-consuming sequence of events and activities. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 4 steps:
* Preparation of a list of all the tasks that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation showed in figure 1. This box will later be filled with other time informations about the project.

[[File:PERT box.png | thumb | center | 500px | '''Figure 1''': PERT box ]]

=== Network diagram ===

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the task and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes just like on figure 2. For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

[[File:PERT network.png | thumb | center | 400px | '''Figure 2''': PERT network with critical path ]]

=== Estimation of the time ===

In this step we estimate the amount of time that can be taken by each activity. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as his longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the tasks which have a null difference between the respective times. Those tasks constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between tasks
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager. Therefore
* No representation of repetitive tasks. Because the project is presented in a network form, a repetitive task would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:PERT network in ms Project.png | thumb | right | 400px | '''Figure 3''': PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project (see figure 3) or Oracle Primavera. PERT charts are used to visualize the dependencies between different tasks. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 400px | '''Figure 4''': Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization. In the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project (see figure 4). Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization. DSM matrices represent basically the same information as a PERT network, which is different activities and their connections. The advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network (see figure 5). However it doesn't give any information concerning timings of activities. It is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | center | 350px | '''Figure 5''': DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
* Project Management Demystified: Today's Tools and Techniques, Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.

Program evaluation and review technique (PERT)

2015-09-27T20:15:53Z

S141938: /* Comparison to other tools */

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects, its advantages and limitations.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

A network diagram is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The activities are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The events are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

The critical path is the path through the network that includes the most time-consuming sequence of events and activities. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 4 steps:
* Preparation of a list of all the tasks that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation showed in figure 1. This box will later be filled with other time informations about the project.

[[File:PERT box.png | thumb | center | 500px | '''Figure 1''': PERT box ]]

=== Network diagram ===

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the task and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes just like on figure 2. For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

[[File:PERT network.png | thumb | center | 400px | '''Figure 2''': PERT network with critical path ]]

=== Estimation of the time ===

In this step we estimate the amount of time that can be taken by each activity. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as his longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the tasks which have a null difference between the respective times. Those tasks constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between tasks
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager. Therefore
* No representation of repetitive tasks. Because the project is presented in a network form, a repetitive task would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:PERT network in ms Project.png | thumb | right | 400px | '''Figure 3''': PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project (see figure 3) or Oracle Primavera. PERT charts are used to visualize the dependencies between different tasks. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 400px | '''Figure 4''': Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother ?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization. In the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project (see figure 4). Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization. DSM matrices represent basically the same information as a PERT network, which is different activities and their connections. The advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network (see figure 5). However it doesn't give any information concerning timings of activities. It is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | center | 350px | '''Figure 5''': DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
* Project Management Demystified: Today's Tools and Techniques, Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.

Talk:Program evaluation and review technique (PERT)

2015-09-27T20:02:46Z

S141938: /* Reviewer 1 - Biankajuh: Feedback */

Anna: Very nice topic! It seems that you have a good grasp on the structure of the article and the theme fits the first article type: method :).

== Reviewer 1 - Biankajuh: Feedback==
# I have find your abstract very well-designed which fulfill the role of introducing the main purpose and highlights of the article. Also commendable that you mention the limitation of the PERT model and talk about the comparative tools as well as the modifications.
'''Answer''' : Extendended the last sentence a bit.
# The article is nicely illustrated with the pictures which help the understanding. Although, I would suggest to name them as ‘’Figure 1, 2, 3, …etc.’’ which would allow to refer to the pictures more specifically. So for example instead of the sentence “This information is presented in a box representation.”, you could say “This information is presented in the box representation showed in Figure 1.”.
'''Answer''': Added the figure numbering and some references in the text to the figures.
#The third figure entitled in “PERT network in MS Project 2013” is quite unclear. Could you increase the quality of the picture?
'''Answer''': Changed it (that's the best I can get)
#In some cases, too long sentences could be substituted by two or three shorter ones to help the understanding. For example: “The essential difference between a PERT chart and DSM is the visualization; DSM matrices represent basically the same information as a PERT network, which is different activities and their connections; the advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network.” (Comparison to other tools) —> Could be changed to: “The essential difference between a PERT chart and DSM is the visualization. DSM matrices represent basically the same information as a PERT network, which is different activities and their connections. The advantage of this representation in DSM is its conciseness compared to PERT, where lots of space is required to have a readable network.”
#Grammatical/Formatting hints:
##Space missing between two sentence: “whereas the events are the nodes.For instance,” (Network diagram),
##No need for space before question mark: “How do they differ from eachother ?” (Comparison to other tools)
#Regarding the Bibliography, I would note to refer all these references within the text of the article at the corresponding spaces.

'''Reviewer 2 – User: s113735'''
Feedback: Program evaluation and review technique (PERT)
Formal Aspects:
*The article clearly follows the “method or tool” structure required. Super!
*The grammar and spelling in the article is at a decently high level. The sentences are short and concise, which makes it a pleasurably read with clear and easy to understand points.
*Your choice of figures are good and in line with the points, you are trying to make. Some figures could, however, be explained a little better (for instance the PERT box).
*Figures are missing references.
*The article has a bibliography, but is otherwise free of references and links. This makes it really hardto check the validity of your points. The article will have to be referenced.

Content Aspects:
*The article is clearly within the scope as it relates directly to a “Program” tool/method.
*The length of the article seems fair, but a few headings and sub-sections could easily be elaborated a bit. (For instance the “process” section: What are the benefits/drawbacks from using the tools you present? Are the tools prescribed or optional? Etc… You explain the overall applications and limitations for the PERT model, but not for the individual tools).
*The “critical path” in Project Management to my knowledge is not “the path that includes the most time consuming tasks” but is instead “the sequence of activities which add up to the longest overall duration”. You clearly show in your article that you know this while ALSO showing you know how to calculate the critical path.
With a little bit sharper terminology and definitions, it would increase the understanding a lot.
*When making a statement like: “But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures.” This definitely need to be referenced.
Other than in a few cases the article is generally void of personal/unverifiable opinions, which is good.
*So far, the article doesn’t link to any other articles on the Wiki. I understand that it might be tough to find something directly related to this specific tool amongst the rather limited topics on the Wiki. I suggest trying to find some broad topics or even Categories to link to when writing. For instance, you might link to “human behaviour” (a category on the Wiki) when writing about the “agreement dimension” in the Stacey Matrix.

Overall Conclusion: The article is written at a high level and is easy to read and understand. Some points could however be elaborated a bit and the article needs to be referenced according to Wiki standards using the
<nowiki><ref> lastname, firstname (year) [www.link.com “linkname”] </ref></nowiki> standard.

== MistaJacob, reviewer 3 ==

=== The feedback will be given in the form: ===
*My feedback
**My feedback

OR

*’’Copy of your text’’
**My feedback

=== Feedback ===
*The general formatting is almost as it’s supposed to be. The pictures though lack the numbering and the references in the text, and you shift with using ‘thumbs’ and placing it in the middle. Consistency can be recommended for a better visual overview.
*The language is clear and easy to read, only with small number of places where i found typo’s, like in “Limitation” where you start and end a sentence with: Therefore
**I will not comment these since they will be obvious to you when you read through your article for corrections.

*I found the article relevant, with a good red thread through it.
*The step by step approach worked as it should. That being said, the reader’s understanding could have been improved if you included a practical example you carried out through all steps
**As you promised in the introduction :)
*in the section “Key Concepts”, the sequence of the bullet point list should be the same as the sequence in which they are explained, or vice versa.
*’’The process of making a PERT analysis can be divided into 4 steps:’’
**you have written 5 bullet points below
*‘’Preparation of a list of all the tasks that will be involved in a given project’’
**I would stick to using ‘activities’ and not ‘tasks’ as you write here.
**There are other places (maybe only one) where you use task as well
*I would suggest that you also explain the term ‘float’, since it appears in your figure
*‘’In this step we estimate the amount of time that can be taken by each activity.’’
**You normally don’t use ‘we’
*‘’A project cannot be completed as long as his longest component isn't finished.’’
**Don’t know whether you would be able to argue your way out of defining a project as being ‘male’ ;)
*‘’Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project.’’
**Double up
*Since you describe the other tool in the comparison very briefly, I would suggest to include links to their respective articles (if they exists)

Program evaluation and review technique (PERT)

2015-09-27T20:01:48Z

S141938: /* Applications */

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects, its advantages and limitations.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

A network diagram is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The activities are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The events are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

The critical path is the path through the network that includes the most time-consuming sequence of events and activities. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 4 steps:
* Preparation of a list of all the tasks that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation showed in figure 1. This box will later be filled with other time informations about the project.

[[File:PERT box.png | thumb | center | 500px | '''Figure 1''': PERT box ]]

=== Network diagram ===

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the task and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes just like on figure 2. For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

[[File:PERT network.png | thumb | center | 400px | '''Figure 2''': PERT network with critical path ]]

=== Estimation of the time ===

In this step we estimate the amount of time that can be taken by each activity. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as his longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the tasks which have a null difference between the respective times. Those tasks constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between tasks
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager. Therefore
* No representation of repetitive tasks. Because the project is presented in a network form, a repetitive task would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:PERT network in ms Project.png | thumb | right | 400px | '''Figure 3''': PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project (see figure 3) or Oracle Primavera. PERT charts are used to visualize the dependencies between different tasks. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 400px | '''Figure 4''': Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother ?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization; in the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project (see figure 4). Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization; DSM matrices represent basically the same information as a PERT network, which is different activities and their connections; the advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network (see figure 5). However it doesn't give any information concerning timings of activities; it is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | center | 350px | '''Figure 5''': DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
* Project Management Demystified: Today's Tools and Techniques, Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.

File:PERT network in ms Project.png

2015-09-27T20:00:18Z

S141938:

Program evaluation and review technique (PERT)

2015-09-27T19:56:22Z

S141938: /* Comparison to other tools */

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects, its advantages and limitations.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

A network diagram is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The activities are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The events are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

The critical path is the path through the network that includes the most time-consuming sequence of events and activities. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 4 steps:
* Preparation of a list of all the tasks that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation showed in figure 1. This box will later be filled with other time informations about the project.

[[File:PERT box.png | thumb | center | 500px | '''Figure 1''': PERT box ]]

=== Network diagram ===

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the task and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes just like on figure 2. For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

[[File:PERT network.png | thumb | center | 400px | '''Figure 2''': PERT network with critical path ]]

=== Estimation of the time ===

In this step we estimate the amount of time that can be taken by each activity. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as his longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the tasks which have a null difference between the respective times. Those tasks constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between tasks
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager. Therefore
* No representation of repetitive tasks. Because the project is presented in a network form, a repetitive task would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:MS project 2013 PERT chart.png | thumb | right | 400px | '''Figure 3''': PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project (see figure 3) or Oracle Primavera. PERT charts are used to visualize the dependencies between different tasks. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 400px | '''Figure 4''': Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother ?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization; in the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project (see figure 4). Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization; DSM matrices represent basically the same information as a PERT network, which is different activities and their connections; the advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network (see figure 5). However it doesn't give any information concerning timings of activities; it is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | center | 350px | '''Figure 5''': DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
* Project Management Demystified: Today's Tools and Techniques, Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.

Program evaluation and review technique (PERT)

2015-09-27T19:55:01Z

S141938: /* Applications */

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects, its advantages and limitations.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

A network diagram is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The activities are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The events are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

The critical path is the path through the network that includes the most time-consuming sequence of events and activities. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 4 steps:
* Preparation of a list of all the tasks that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation showed in figure 1. This box will later be filled with other time informations about the project.

[[File:PERT box.png | thumb | center | 500px | '''Figure 1''': PERT box ]]

=== Network diagram ===

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the task and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes just like on figure 2. For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

[[File:PERT network.png | thumb | center | 400px | '''Figure 2''': PERT network with critical path ]]

=== Estimation of the time ===

In this step we estimate the amount of time that can be taken by each activity. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as his longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the tasks which have a null difference between the respective times. Those tasks constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between tasks
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager. Therefore
* No representation of repetitive tasks. Because the project is presented in a network form, a repetitive task would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:MS project 2013 PERT chart.png | thumb | right | 400px | '''Figure 3''': PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project (see figure 3) or Oracle Primavera. PERT charts are used to visualize the dependencies between different tasks. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 400px | '''Figure 4''': Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother ?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization; in the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project. Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization; DSM matrices represent basically the same information as a PERT network, which is different activities and their connections; the advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network. However it doesn't give any information concerning timings of activities; it is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | center | 350px | '''Figure 5''': DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
* Project Management Demystified: Today's Tools and Techniques, Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.

Program evaluation and review technique (PERT)

2015-09-27T19:54:30Z

S141938: /* Network diagram */

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects, its advantages and limitations.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

A network diagram is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The activities are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The events are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

The critical path is the path through the network that includes the most time-consuming sequence of events and activities. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 4 steps:
* Preparation of a list of all the tasks that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation showed in figure 1. This box will later be filled with other time informations about the project.

[[File:PERT box.png | thumb | center | 500px | '''Figure 1''': PERT box ]]

=== Network diagram ===

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the task and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes just like on figure 2. For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

[[File:PERT network.png | thumb | center | 400px | '''Figure 2''': PERT network with critical path ]]

=== Estimation of the time ===

In this step we estimate the amount of time that can be taken by each activity. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as his longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the tasks which have a null difference between the respective times. Those tasks constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between tasks
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager. Therefore
* No representation of repetitive tasks. Because the project is presented in a network form, a repetitive task would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:MS project 2013 PERT chart.png | thumb | right | 400px | '''Figure 3''': PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project or Oracle Primavera. PERT charts are used to visualize the dependencies between different tasks. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 400px | '''Figure 4''': Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother ?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization; in the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project. Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization; DSM matrices represent basically the same information as a PERT network, which is different activities and their connections; the advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network. However it doesn't give any information concerning timings of activities; it is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | center | 350px | '''Figure 5''': DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
* Project Management Demystified: Today's Tools and Techniques, Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.

Program evaluation and review technique (PERT)

2015-09-27T19:41:34Z

S141938: /* Network diagram */

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects, its advantages and limitations.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

A network diagram is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The activities are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The events are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

The critical path is the path through the network that includes the most time-consuming sequence of events and activities. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 4 steps:
* Preparation of a list of all the tasks that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation showed in figure 1. This box will later be filled with other time informations about the project.

[[File:PERT box.png | thumb | center | 500px | '''Figure 1''': PERT box ]]

=== Network diagram ===

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the task and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes just like on figure 2.For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

[[File:PERT network.png | thumb | center | 400px | '''Figure 2''': PERT network with critical path ]]

=== Estimation of the time ===

In this step we estimate the amount of time that can be taken by each activity. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as his longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the tasks which have a null difference between the respective times. Those tasks constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between tasks
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager. Therefore
* No representation of repetitive tasks. Because the project is presented in a network form, a repetitive task would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:MS project 2013 PERT chart.png | thumb | right | 400px | '''Figure 3''': PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project or Oracle Primavera. PERT charts are used to visualize the dependencies between different tasks. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 400px | '''Figure 4''': Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother ?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization; in the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project. Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization; DSM matrices represent basically the same information as a PERT network, which is different activities and their connections; the advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network. However it doesn't give any information concerning timings of activities; it is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | center | 350px | '''Figure 5''': DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
* Project Management Demystified: Today's Tools and Techniques, Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.

Program evaluation and review technique (PERT)

2015-09-27T19:40:51Z

S141938: /* Preparation phase */

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects, its advantages and limitations.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

A network diagram is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The activities are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The events are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

The critical path is the path through the network that includes the most time-consuming sequence of events and activities. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 4 steps:
* Preparation of a list of all the tasks that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation showed in figure 1. This box will later be filled with other time informations about the project.

[[File:PERT box.png | thumb | center | 500px | '''Figure 1''': PERT box ]]

=== Network diagram ===

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the task and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes.For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

[[File:PERT network.png | thumb | center | 400px | '''Figure 2''': PERT network with critical path ]]

=== Estimation of the time ===

In this step we estimate the amount of time that can be taken by each activity. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as his longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the tasks which have a null difference between the respective times. Those tasks constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between tasks
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager. Therefore
* No representation of repetitive tasks. Because the project is presented in a network form, a repetitive task would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:MS project 2013 PERT chart.png | thumb | right | 400px | '''Figure 3''': PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project or Oracle Primavera. PERT charts are used to visualize the dependencies between different tasks. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 400px | '''Figure 4''': Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother ?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization; in the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project. Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization; DSM matrices represent basically the same information as a PERT network, which is different activities and their connections; the advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network. However it doesn't give any information concerning timings of activities; it is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | center | 350px | '''Figure 5''': DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
* Project Management Demystified: Today's Tools and Techniques, Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.

Program evaluation and review technique (PERT)

2015-09-27T19:39:39Z

S141938:

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects, its advantages and limitations.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

A network diagram is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The activities are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The events are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

The critical path is the path through the network that includes the most time-consuming sequence of events and activities. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 4 steps:
* Preparation of a list of all the tasks that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation. This box will later be filled with other time informations about the project.

[[File:PERT box.png | thumb | center | 500px | '''Figure 1''': PERT box ]]

=== Network diagram ===

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the task and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes.For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

[[File:PERT network.png | thumb | center | 400px | '''Figure 2''': PERT network with critical path ]]

=== Estimation of the time ===

In this step we estimate the amount of time that can be taken by each activity. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as his longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the tasks which have a null difference between the respective times. Those tasks constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between tasks
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager. Therefore
* No representation of repetitive tasks. Because the project is presented in a network form, a repetitive task would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:MS project 2013 PERT chart.png | thumb | right | 400px | '''Figure 3''': PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project or Oracle Primavera. PERT charts are used to visualize the dependencies between different tasks. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 400px | '''Figure 4''': Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother ?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization; in the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project. Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization; DSM matrices represent basically the same information as a PERT network, which is different activities and their connections; the advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network. However it doesn't give any information concerning timings of activities; it is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | center | 350px | '''Figure 5''': DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
* Project Management Demystified: Today's Tools and Techniques, Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.

Talk:Managing Uncertainty and Risk on the Project

2015-09-22T20:23:06Z

S141938:

Review1, Buurbuur:
- I found the topic very interesting and very relevant for this course.
- Good that many point are illustrated with an appropriate figure.
- However I find the scope very broad, maybe choose only to focus on project or portofolio management.
- In the ''definition'' section i find it difficult to understand and navigate between all the different definitions, maybe it could make it more easy and understandable if you make a grid to show the difference. Or list them up on bulletspoints
- Secure that the article fit to one of the two article types i relation to the required topics
- However I find the figures clear and understandable
- Good that there are references on every figure

Anna: It is an interesting and very relevant topic, however, I would suggest that you try to narrow down the scope and focus your article on one method/tool that can be applied for managing uncertainty and risk in a project. Remember that your article has to fit one of the two article types and the required structure :)

Reviewer 2:Andkamp
*Great use of English and nice sentences structure
*Great subject but, very broad, needs to be narrowed a little bit
*Nice figures, but the matrix with the papers is something I expected to be illustrated in matrix and not a Figure, in order to maintain the wiki style of the article.
*Nice Referencing of the figures, although it hadn't any inter-wiki links or in text links.
*The interest of a practitioner could be greater if there was more focusing in aspects of this subject.
*Profound relation with project management
*The good structure assures logical flow
*Extremely poor reference material for such extended article, that could lead someone with bad intensions to think that there's some amount of plagiarism
*Expected to see pros/cons
*Implementations would narrow the whole subject and make it more interesting
Generally speaking a more wiki style text, with hyperlinks,more bibliography and see also section would be more appropriate to this great text.

== Reviewer 3 - s141938 ==

+

* abstract at the beginning
* captions and figure numbering
* gramatically correct. easy and pleasant to read
* nice references to the graphs - everything is explained nicely

-
* separate consequences in the definitions into paragraphs
* "In the beginning of the a project the uncertainty is very high and depending on the size of the project and to decrease the mission uncertainty it can some extend be used” - I think you're missing something at some point
* really broad - maybe give some methods that are used to minimize risk and uncertainty cause this would stick more with the method type of article
* Advantages and limitations ? (required in the method type article)
* Add more references for higher credibility ;)
* maybe restructure the definition section, to make the article easier to scan quickly

Conclusion: Great article and properly written, but needs to be restructured a bit for quicker scanning of the article and to fit the method article type.

Talk:Project Execution Model (PEM)

2015-09-22T20:15:35Z

S141938:

Mette: Very nice topic choice that fits the requirements for the type of article. Remember the structure of a "method article". Look forward to reading more about this tool.

Reviewer 1:Andkamp

*Describes an interesting method developed by Novo Nordisk, a nice blend between case study and method description
*Minor English mistakes, that can be corrected through second time reading
*Good presentation of the topics, however some minor grammar mistakes make it a little more difficult to be read
*Nice figures, but missing captions and misplacement could provide a better outlook.
*Main points are clear but not extensively described, in order the reader to get a better understanding of the topic.
*No figure reference
*More effort in inter-wiki links and hyperlinks in the text should be done
*Better matrix of plan communication of stakeholders
*Missing references and bibliography
*Interesting subject with various aspects
*Length of the article is small, as probably it is unfinished, but there is a clear enthusiasm on that subject
*Phases makes a concrete structure of the article but the sections should be better presented in the table of contents.
*It would be nice to see implementations on other business, as well as the pros and cons of this method
*All in all, a nice subject that needs more effort in order to be useful and be connected with subjects such as Project Evaluation and Selection for the Formation of the Optimal Portfolio

== Reviewer 2 - s141938 ==

+
* clear and concise => easy to read
* ideas presented in bullet points. Good idea
* Structure of a method visible
* planned links to other wiki pages. Great idea !

-
* Remember to add captions and figure numbering
* Write an abstract at the beginning and make a first section with quick explanation with the current intro => nicer layout and will remove the image from the introduction
* In the new first section give a brief description of the phases so that I have a small overview of the whole thing
* no need of making sections in phase 2, unless it will be elaborated
* This is it for now. I’ll give you more details once finished

== Reviewer 3 - Biankajuh ==
# I have find the abstract of your article very well-designed which fulfill the role of introducing the main purpose and highlights of the article including a brief introduction to the PEM model. I really like the fact that you have chosen such a real life method as the PEM model used by Novo Nordisk.
# I appreciate your idea of discussing your model by comparing it with other relevant project models as you have indicated it in the current last paragraph title (Discussion of Novo Nordisk's Project Execution Model compared to other project models).
# The article is nicely illustrated with the pictures which help the understanding. Although, I would suggest to name them as ‘’Figure 1, 2, 3, …etc.’’ which would allow to refer to the pictures more specifically at the relevant place of the text.
# "A project is defined as: "A temporary endeavor undertaken to create a unique product, service or result"." --> Could you expound and describe more what do you mean under this project title? As for me, it is not so clear.
# For further investigation:
## I would suggest to consider writing about the concrete applications and limitations of the model chosen.
## It would be also nice to focus on the references and make a bibliography section at the end of the article.

Talk:Financial Portfolio Optimization Methods

2015-09-22T20:08:21Z

S141938:

Josef: Thank you for an interesting, and already rather detailed, Wiki article.

What I struggle with is the relationship of your article with the management of project portfolios. There are in fact serious limitations to the applicability of financial portfolio theory to project portfolios, for example the assumptions that you can invest/divest into options without changing their risk/return balance, or the assumption that you can actually divest from options ("selling" a failing project will almost always be impossible, as I am not aware of a secondary market for projects).
I am not sure how we can "salvage" all the details you have already produced. What I would suggest is to focus on what part of financial portfolio management theory is applicable to project portfolio management, or better, why it is not applicable.

== Reviewer 1 – User: s141938 ==

+

* Methods are really thoroughly described. Nothing is left out. I am wondering if you could specify which ones are popular and which ones have been left out*
* When you’re describing the formulas, you describe also the meaning of the variables. Perfect! But some have been left out like in CVar and semi-variance - the z and T and r
* I like the application part at the end of the article, showing where this optimization is still in use. But then again, could you give more details about which method is more popular
* References are as they should be : quick description, well formatted, good sources
* Links to other articles. Keep it that way
* see also section is nice

-
* You could write a quick abstract at the beginning to give a general overview of the article
* Like I have already mentioned check all of the variables in each formulas (CVar, semi-variance - the z and T and r, )
* I was a bit confused by the usage of different words sometimes. For instance in the mean variance method you are talking about bonds, then in other methods it’s about portfolios. I think that you could explain the key concepts more thoroughly in the first block and make it a separate paragraph, so that it is easy to spot when going through the article quickly
* Try to structure things a bit. For instance separate the first block into „Introduction" and "main concepts and principles"
* Elaborate the idea of financial portfolio, unless there is nothing more to add
* Divide the text into paragraphs -> might be easier to read or at least scan
* Could you be a bit more precise about the assumptions - who made them ?
* I think it would be nice to have a comparison of the effectiveness of the different methods
* SOmetimes I think you can drop some of the references like in the following example - mixed integer programming for portfolio selection with pragmatic characteristics [24] [25] [26] [27] [28]
* COuld you write the advantages of the methods - it would stick more to the structure of a method article (unless there are no advantages)
* chech the "in order to” cause there are plenty of missing „to” like in "In order a business to minimize”

Conclusion : Nice article, lots of information but try to structure things to make it more reader-friendly.

== Reviewer 2 - Biankajuh ==
# I have find the description of the models very accurate. Also commendable that you mention the implementations and the limitation/disadvantages of the certain Financial Portfolio Optimization Methods. Furthermore, I really like the usage of direct links to other articles and websites. It shows a very precise job and makes it easy to follow and read up in the certain topic.
# Structural suggestions:
## I would suggest to write a brief abstract section for the beginning of the article. That would help the reader to find a short few sentences summary about the main aspect and purpose of this work.
## Did I assume correctly that the section of “Financial Portfolio Optimization Methods in PPM” is more about the history? Would it make more sense to refer on it rather as History perhaps also in the title of the section?
# As for me, you could make the article easier to read by defining some expressions such as “assets” in the given circumstances (similarly like you defined “investor” in the same paragraph). Please also consider to define abbreviation such as MPT. (Financial Portfolio Optimization Methods in PPM)
# The article is nicely illustrated with the pictures which help the understanding. Although, I would suggest to name them as ‘’Figure 1, 2, 3, …etc.’’ which would allow to refer to the pictures at the relevant place of the text. For example: “Figure shows an example where all the possible portfolios which are formed based on the expected return and risk relations.” - Here you could specify by saying Figure 2.
# At the first picture entitled as “Translation of MPT criterias to PPM criterias”, you use MPT in the title and also in the article above it, however, it says MPM in the figure itself. Are MPT and MPM referring to the same subject? Could you define what they are?
# Grammatical/Formatting hints:
## “Application of methods of financial portfolio optimization can help a project manager to evaluate projects taking in consideration the interaction and influence of other projects” (Financial Portfolio Optimization Methods in PPM) —> Dot is missing from the end of the sentence. Plus I would suggest to change the word order for the following: “Application of methods of financial portfolio optimization can help a project manager to evaluate projects taking the interaction and influence of other projects in consideration.”

'''Reviewer 3 – User: s113735'''

Feedback:

Formal Aspects:
*The article clearly follows the “method or tool” requirement for the wiki article
*I recognize very few spelling errors. Things I were able to find are small mistakes like omitting a word or missing a large letter in the beginning of a new sentence:
“In order [for] a business to minimize the danger of exposure to a failed project… “
“… strategic alignment and resource levelling. [A]<strike>a</strike>pplication of such methods…”
*I am not sure I fully understand figure 1: “Tranlation of MPT criterias to PPM criterias”, maybe this can be elaborated better? You second figure is well explained and easy to understand.
*You make great use of the <nowiki><math></math></nowiki> tool in your article. And although the content is quite complex, it gives the article a wiki-“esque” feeling, which is good.

Content Aspects:

*The article is clearly within the topic scope, as it directly relates to a “portfolio” topic
*You clearly have extensive knowledge of the subject and your very rigid use of references show me that you back up every statement you make. Sadly, (and this is of no fault of yours or a drawback to the content of the article) most of your references are hard-copy (aka. Book) references so I do not currently have to possibility to review your sources.
*“Northwestern” part of the curve… Why not “Top left?”
*I have no idea what “[καινουριο paper CVaR]” (in the CVaR model section) is or means, maybe this is something you left by mistake in the article?
*The size, quality and references of the article are definitely up to par. It is very clear that you know much more about the topic than I ever will.

Overall conclusion:

As mentioned, it is very clear by the content and quality of the article, that you have extensive knowledge of the tools you present. The only, albeit minor, drawback is that I feel the article is not very engaging. I think the article could benefit a lot from a few “bridging” sentences about the '''general''' purpose of the models you present – some more example uses or sentences of how exactly they relate to portfolio management. I think that would really bind the article together.

Talk:Financial Portfolio Optimization Methods

2015-09-22T19:38:04Z

S141938:

Program evaluation and review technique (PERT)

2015-09-21T19:22:57Z

S141938: /* Bibliography */

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

A network diagram is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The activities are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The events are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

The critical path is the path through the network that includes the most time-consuming sequence of events and activities. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 4 steps:
* Preparation of a list of all the tasks that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation. This box will later be filled with other time informations about the project.

[[File:PERT box.png | thumb | center | 500px | PERT box ]]

=== Network diagram ===

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the task and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes.For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

[[File:PERT network.png | thumb | center | 400px | PERT network with critical path ]]

=== Estimation of the time ===

In this step we estimate the amount of time that can be taken by each activity. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as his longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the tasks which have a null difference between the respective times. Those tasks constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between tasks
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager. Therefore
* No representation of repetitive tasks. Because the project is presented in a network form, a repetitive task would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:MS project 2013 PERT chart.png | thumb | right | 400px | PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project or Oracle Primavera. PERT charts are used to visualize the dependencies between different tasks. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 400px | Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother ?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization; in the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project. Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization; DSM matrices represent basically the same information as a PERT network, which is different activities and their connections; the advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network. However it doesn't give any information concerning timings of activities; it is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | center | 350px | DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.
* Project Management Demystified: Today's Tools and Techniques, Geoff Reis, provides real life anecodtes about the method, discusses how it became famous and why it is less used now.

Program evaluation and review technique (PERT)

2015-09-21T19:21:01Z

S141938: /* Bibliography */

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

A network diagram is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The activities are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The events are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

The critical path is the path through the network that includes the most time-consuming sequence of events and activities. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 4 steps:
* Preparation of a list of all the tasks that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation. This box will later be filled with other time informations about the project.

[[File:PERT box.png | thumb | center | 500px | PERT box ]]

=== Network diagram ===

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the task and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes.For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

[[File:PERT network.png | thumb | center | 400px | PERT network with critical path ]]

=== Estimation of the time ===

In this step we estimate the amount of time that can be taken by each activity. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as his longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the tasks which have a null difference between the respective times. Those tasks constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between tasks
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager. Therefore
* No representation of repetitive tasks. Because the project is presented in a network form, a repetitive task would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:MS project 2013 PERT chart.png | thumb | right | 400px | PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project or Oracle Primavera. PERT charts are used to visualize the dependencies between different tasks. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 400px | Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother ?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization; in the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project. Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization; DSM matrices represent basically the same information as a PERT network, which is different activities and their connections; the advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network. However it doesn't give any information concerning timings of activities; it is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | center | 350px | DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==

* ESSENTIALS OF MANAGEMENT, Andrew DuBrin, Section "Program Evaluation and Review Technique", General overview and presentation of the method with all of the steps.
* Programming and Scheduling Techniques, Thomas Uher,Adam S. Zantis, Chapter 13, presentation of the method with an emphasis on the event side compared to the critical path method.
* The Handbook of Project Management: A Practical Guide to Effective Policies, Trevor L. Young, presentation of the method from a visual side (box drawing and step by step filling)
* Entrepreneurship Development, S. Anil Kuma, presentation of the method with a discussion of the advantages and disadvantages.
* https://www.mindtools.com/critpath.html, comparison of the Critical Path Analysis and PERT, how they differ and how are they connected.

Program evaluation and review technique (PERT)

2015-09-21T18:56:26Z

S141938: /* Comparison to other tools */

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

A network diagram is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The activities are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The events are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

The critical path is the path through the network that includes the most time-consuming sequence of events and activities. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 4 steps:
* Preparation of a list of all the tasks that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation. This box will later be filled with other time informations about the project.

[[File:PERT box.png | thumb | center | 500px | PERT box ]]

=== Network diagram ===

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the task and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes.For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

[[File:PERT network.png | thumb | center | 400px | PERT network with critical path ]]

=== Estimation of the time ===

In this step we estimate the amount of time that can be taken by each activity. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as his longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the tasks which have a null difference between the respective times. Those tasks constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between tasks
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager. Therefore
* No representation of repetitive tasks. Because the project is presented in a network form, a repetitive task would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:MS project 2013 PERT chart.png | thumb | right | 400px | PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project or Oracle Primavera. PERT charts are used to visualize the dependencies between different tasks. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

[[File:Gantt chart example.png | thumb | right | 400px | Gantt chart example ]]

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother ?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization; in the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project. Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization; DSM matrices represent basically the same information as a PERT network, which is different activities and their connections; the advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network. However it doesn't give any information concerning timings of activities; it is less focused on the planning but more on the management.

[[File:DSM Tutorial BasicDSM.jpg | thumb | center | 350px | DSM equivalent of a PERT network ]]

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==

File:DSM Tutorial BasicDSM.jpg

2015-09-21T18:48:33Z

S141938: DSM example

DSM example

File:Gantt chart example.png

2015-09-21T18:42:28Z

S141938: Gantt chart example

Gantt chart example

Program evaluation and review technique (PERT)

2015-09-21T18:41:07Z

S141938: /* Applications */

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

A network diagram is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The activities are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The events are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

The critical path is the path through the network that includes the most time-consuming sequence of events and activities. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 4 steps:
* Preparation of a list of all the tasks that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation. This box will later be filled with other time informations about the project.

[[File:PERT box.png | thumb | center | 500px | PERT box ]]

=== Network diagram ===

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the task and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes.For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

[[File:PERT network.png | thumb | center | 400px | PERT network with critical path ]]

=== Estimation of the time ===

In this step we estimate the amount of time that can be taken by each activity. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as his longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the tasks which have a null difference between the respective times. Those tasks constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between tasks
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager. Therefore
* No representation of repetitive tasks. Because the project is presented in a network form, a repetitive task would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

[[File:MS project 2013 PERT chart.png | thumb | right | 400px | PERT network in MS Project 2013 ]]

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project or Oracle Primavera. PERT charts are used to visualize the dependencies between different tasks. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother ?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization; in the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project. Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization; DSM matrices represent basically the same information as a PERT network, which is different activities and their connections; the advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network. However it doesn't give any information concerning timings of activities; it is less focused on the planning but more on the management.

nd progress of the project. Timings in Gantt charts can be esGantt charts are used to display the timing of activities and progress of the project. Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization; DSM matrices represent basically the same information as a PERT network, which is different activities and their connections; the advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network. However it doesn't give any information concerning timings of activities; it is less focused on the planning but more on the management.

timated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==

File:MS project 2013 PERT chart.png

2015-09-21T18:38:43Z

S141938: PERT network in MS project 2013

PERT network in MS project 2013

Program evaluation and review technique (PERT)

2015-09-21T18:37:18Z

S141938: /* Network diagram */

[[ Category:Project Management | Program evaluation and review technique ]]
[[ Category:Product Development | Program evaluation and review technique ]]

The Program Evaluation and Review Technique (PERT) is a method used in project management for planning, scheduling and coordinating the tasks of a project. It is based on a network diagram analysis of the different tasks that are involved. PERT is specifically suited for large, complex and nonrepititive projects. The aim of this article is to give an overview of this method with examples of applications and a comparison to other existing network based project management tools. It will also explore the usage of this method in todays projects.

== General overview ==

Program Evaluation and Review Technique, as a network analysis tool, gives the possibility to analyze large projects task by task and to estimate the amount of time that will be spent on each task. It was first introduced in the 1950s by the US Navy, during the works on the Polaris missiles project. It was a large and complex project involving multiple contractors and an effective planning tool was a necessity to finish the project successfully. The project has been finished long before the deadline and most of the people attributed this success to PERT.

== Key concepts ==

PERT has several concepts that need to be defined, to understand the whole method. Those are :
* Activities
* Events
* Network diagrams
* Critical path

A network diagram is a visual representation of a project's schedule. It presents all the information about the project on a time basis like the tasks, their starting/ending times, total duration. Using this kind of representation makes the whole management process much easier and less error-prone.

The activities are the tasks that need to be completed. Each task has a predefined duration, a priority, a cost and an amount of workers associated with it. On a network level, they are represented as nodes connected by arrows. They can have predecessors - other tasks that need to be completed before them - and successors - tasks that can start only once this one has finished.

The events are points in time marking a phase of an activity like the start or the completion. Events can relate to one or more activities.

The critical path is the path through the network that includes the most time-consuming sequence of events and activities. Hence it represents also the total time that will be needed to complete the project. Any delay that occurs in one of the activities on this path will affect the completion date.

== The process ==

The process of making a PERT analysis can be divided into 4 steps:
* Preparation of a list of all the tasks that will be involved in a given project
* Creation of a network diagram
* Estimation of the time required to finish each activity
* Calculation of the critical path
* Network analysis

=== Preparation phase ===

PERT starts with a standard step of defining the activities that will be involved in the project. This information is presented in a box representation. This box will later be filled with other time informations about the project.

[[File:PERT box.png | thumb | center | 500px | PERT box ]]

=== Network diagram ===

Once the basic information about the activities has been gathered, the activities need to be put in order. The priority of the task and the dependencies between them are taken into consideration. In the network, activities are represented as arrows, whereas the events are the nodes.For instance, the preparation of the base of a building would be decoupled into "starting of preparation" and "end of preparations".

[[File:PERT network.png | thumb | center | 400px | PERT network with critical path ]]

=== Estimation of the time ===

In this step we estimate the amount of time that can be taken by each activity. This time can be determined using a probabilistic or a deterministic approach. Three times need to be defined :
* the optimistic time (short time)
* the pessimistic time (shortest time)
* the normal time (most likely time)

The optimistic time (O) is the shortest time an activity will take if everything goes right. In general, it is highly improbable that the project will finish in this time, due to all the other factors.

The pessimistic time (P) is the longest time that an activity will take. During the calculations, several scenarios need to be considered with their respective probability in order to have a quite precise value.

The normal time (M) is the most likely time of an activity. Usually, it is determined using the time other similar activities took in other projects. For instance, the time needed to build a cockpit for one aircraft might be based on the average time it took to build cockpits for comparable aircraft in the past. Using these three times one can calculate the expected time of an activity with the formula below :
Expected time = O + 4M + P / 6

It is basically an average of all of the times mentioned, but the normal time is given a higher weight, since it is the most probable. The expected time will be later used in the PERT diagram.

=== Critical path estimation ===

Once all the time information has been gathered about the different activities, it is possible to estimate the total duration of the project and the starting and ending dates. Determining the critical path comes down to identifying the path that takes the most time. A project cannot be completed as long as his longest component isn't finished. Here are the steps to find this path :
* Step 1 : Starting from the first activity, write the starting and ending times, by adding the duration to the ending time of the preceding activity.
* Step 2 : Make the same thing but from the end and substract the times instead of adding.
* Step 3 : Having the starting times and ending times calculated in two different ways, we can identify the tasks which have a null difference between the respective times. Those tasks constitute the critical path.

=== Time cost trade-offs and resource allocation ===

Having a first estimate of the time necessary to complete the project, it is possible to make a few changes to the plan and compress it a bit. In this step, the manager can decide which activities could be finished faster by reallocating resources properly or increasing them.

=== Project control ===

Having a clear plan of action, the project can finally be started. Every activity is monitored and checked on the schedule. Thanks to a clear representation of the project, in any case, the schedule can be reanalyzed and resources can be managed properly, but this step might be quite time-consuming and can lead to errors. Sometimes, especially at the beginning of the project, one change in an activity can cause the modification of the whole network, leading to a recalculation of the whole plan, which might be longer than necessary.

== Applications and limitations ==

PERT, like other methods, has its pros and cons. Its application can some projects bring a huge benefit, but can also make a disaster in others. The choice of this tool must be well thought before.

=== Advantages ===

The advantages of PERT are :

* Compels to plan and predict project before start. The planning of the project is made in details, resulting in less surprises later.
* Better management of resources. Since we have a detailed plan, we can precisely manage all of the resources, sometimes leading to a reduction of costs of the whole project.
* Focus on the critical activities.
* Good control over the project from the beginning; weak points of the project located right from the start. Gives the possibility to adapt quickly to the situation
* Provides updated information about the project
* Clear view of the dependencies between tasks
* Accurate time estimation thanks to the 3-way computation of the total timing.

=== Limitations ===

PERT limitations are :

* Emphasis only in time and not cost. This method does not present a model to estimate the costs of the project, therefore it is totally dependent on the managers skills and assumptions.
* Lots of analysis during control. Although a good plan can reduce the time of the whole project, making such a detailed plan is time-consuming, which leads to no time gain at all.
* Errors in time estimation might lead to miscalculations. Even if the 3-way estimate was considered an advantages, it is still based on assumptions and data given by the manager. Therefore
* No representation of repetitive tasks. Because the project is presented in a network form, a repetitive task would be represented as an inifinite loop, which could prevent us to determine the critical path.

=== Applications ===

PERT is a tool that can be useful in big and complex projects like in the construction industry. As mentioned in the introduction, it was created during the Polaris missile project and had a huge popularity afterwards. But soon, project managers and companies have found that it is too ineffective and error-prone to use it, causing lots of failures. The main reason behind it was the lack of IT tools, which had not the same abilities as now. Another major point was the update step in this method, which requires to reorganize the whole plan and in the case of large projects, this can be a time consuming and confusing step.

Nowadays the software and hardware part is not a problem anymore. Many management software include PERT charts as part of their functionalities like Microsoft Project or Oracle Primavera. PERT charts are used to visualize the dependencies between different tasks. To see the timing and progress of the project another similar tool is widely used, the Gantt charts. More popular than PERT are the Critical Path diagrams, in which nodes represent the activities, a more readable representation.

== Comparison to other tools ==

As mentioned, PERT belongs to the family of tools based on network analysis. This category includes also other tools like the Critical Path Analysis, the matrix-based Design Structure Matrix, petri nets. How do they differ from eachother ?

PERT and Critical Path Analysis are highly related, since one of the steps in PERT is to find the critical path of the project. They differ mainly on the way the timing is estimated and the visualization; in the Critical Path Analysis the activities are represented as nodes, whereas PERT uses nodes to represent events.

Gantt charts are used to display the timing of activities aGantt charts are used to display the timing of activities and progress of the project. Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization; DSM matrices represent basically the same information as a PERT network, which is different activities and their connections; the advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network. However it doesn't give any information concerning timings of activities; it is less focused on the planning but more on the management.

nd progress of the project. Timings in Gantt charts can be esGantt charts are used to display the timing of activities and progress of the project. Timings in Gantt charts can be estimated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

Design Structure Matrix (DSM) is a modeling technique based on network analysis that can be used for the design, development and management of complex systems. The essential difference between a PERT chart and DSM is the visualization; DSM matrices represent basically the same information as a PERT network, which is different activities and their connections; the advantage of this representation is its conciseness compared to PERT, where lots of space is required to have a readable network. However it doesn't give any information concerning timings of activities; it is less focused on the planning but more on the management.

timated in the same way as in PERT and the whole process of building Gantt charts is almost identical to PERTs process. The use case is the only difference; because Gantt charts have a simplier structure and a better visualization, their usage is much wider and they appear more often in software tools.

== Other modified versions ==

Although PERT is not as popular as it used to be, scientists have tried to enhance it in different ways, mainly the computation of the duration of activities, since its the weakest point of this method. Here is a short list of some other PERT versions :
* GERT - enhances PERT with the possibility of making loops and multiple branches, leading to different results.
* PERT II - usage of a stochastic approach to determine the time of an activity; usage of a cumulative distribution function to determine it.
* PERTBN (Bayesian network) - usage of bayesian networks to determine the duration of the activities.
* RPERT (repetetive PERT) - usage of PERT in repetitive projects.

== Bibliography ==