Revision as of 11:55, 16 September 2016

The Critical Path Method is a step by step technique that is used to schedule a set of project activities. It analysis what activities are least flexible and the project duration is predicted based on the activities that fall along the critical path. The critical path is the longest sequence of activities in a project plan which must be completed on time in order for the project to complete on the predetermined scheduled date.^[1] By delaying an activity on the critical path leads to a delay on the completion time of the entire project as these activities have no slack. Activities along the path cannot start until the predecessor activity is completed. When using CPM to plan a project a graphical diagram is often represented showing how each activity is related to the others.^[2] This method is one of several tools that is important to keep the project on track and is convenient for all forms of projects, including research projects, product development, construction industry, maintenance and many more.

A joint venture between the Dupont chemical company and computer firm Remington Rand Univac led to a development of the Critical Path Method in the 1956 to tackle the interrelationships of separate activities within a project schedule.^[3]

In this article the Critical Path Method (CPM) is described, a step by step guidance on how to apply the method is discussed and the tradeoff between cost and time are analyzed. Furthermore, a comparison to other project management techniques is performed and its limitations and advantages are addressed.

Overview

Introduction and purpose of CPM

Figure 1: Project life cycle.^[4]

“A project is a temporary endeavor undertaken to create a unique product or service”.^[5] The major goal of a project is to satisfy customer’s needs and achieve an organizations’s strategic plan. Projects are unique as they are different in some distinguishing way from all other projects. They have a life cycle were the life span is limited and there are predictable changes in level of effort and focus over the life of the project. Project life cycle generally passes sequentially through four stages: defining, planning, executing and delivering. This is illustrated in Figure 1.^[6]

Figure 2: Triple constraint (also known as the Project Management Triangle).^[7]

To meet project requirements, it is important to have a good knowledge of project management. “If you fail to plan you are planning to fail” is a phrase often used. This can be related to project management, which is an application of knowledge, skills and a set of tools that improves the ability to plan, implement, and manage activities to accomplish specific organizational objectives. Not only is project management a set of tools, it is also a results-oriented management style that places a premium on building collaborative relationships among a diverse cast of characters. ^[6]

When managing projects, it is crucial to have a good understanding of the Triple constraint (also referred to the Project Management Triangle). These constraints, time, scope and cost, form a triangle with a quality in the center as can be seen in Figure 2(fá heimild???). They are all fully inter-related, which means that if one side is altered the other two attributes will be affected in some manner. These constraints must be handled effectively for successful completion of any project as well as for the company to meet their customer quality requirement.^[8] In order for this to be fulfilled the CPM technique can be useful.

History

In the 1950’s The Critical Path Method was developed by a Dupont engineer, Morgan R. Walker and a Remington-Rand computer expert, James E. Kelly, Jr. They created a unique way of representing the operations in the system, which involved using unique arrow filled diagrams. At the similar time, the U.S. Navy initiated a project called Program Evaluation Research Task (PERT). The purpose of that was to provide naval management with an effective manner by which they could periodically evaluate the information of the new Fleet Ballistic Missile program. With this the US Navy could obtain valid information of the progress of the project and also have a reasonable accurate projection of the completion of the project as desired. It is worth mentioning that PERT does not include the quantity, quality and cost information, it only deals with the time constraints.^[9] PERT-CPM was a successful tool for the hardware-oriented programs, but its application in resource management problems was limited. As CPM techniques were modified and designed to operate on the smaller new computer systems, they proved useful in smaller projects such as design and marketing of new products, maintenance and shutdown schedules, and research and development programs.Cite error: Closing </ref> missing for <ref> tag

Moving on to the CCM which is built on CPM. Both methods are “Critical” and as their name suggest there are similarities and differences among the two of them. The main differences are that CPM involves the calculation of ES, EF, LS, LF and SL through forwards and backward passes in the project and focuses on the sequence of activities and the estimated duration of individual task in a straight forward manner. Task buffers are added to each task. On the other hand, CCM just put tasks together in a chain by considering the minimal time needed for individual tasks. An overall project buffer is combined to the end of the project chain. ^[10]

Advantages and disadvantages/limitations of CPM

CPM tool has proved to be very valuable and beneficial when it comes to managing projects. Advantages of using this method are many and the list could get rather long. Listed here below are few of the advantages that organisations could gain by using CPM: ^{[11] [12]}

• The greatest advantage of CPM can be seen in the planning stage, were the user is required to think through a project logically and with sufficient detail to establish form, clear project objectives, activities and specification. This helps preventing the chance of overlooking necessary activities and goals of a project.
• CPM provides a realistic and disciplined method for determining how to attain the project objectives and for communicating and documenting the project plans, schedules, time and cost performance clearly and concisely in the scheduling stage, where a time chart is constructed for each activity.
• In the monitoring stage, CPM identifies the most critical elements in the plan making the managers focusing on the activities that are most constraining on the scheduling. CPM will generate new schedules when there are changes in the durations of the activities. And as technical or procedural changes are considered, CPM provides an easy method for evaluating the effects these changes have on the overall project schedule.

Moving on the disadvantages and limitations of CPM. As for most of the management methods available, CPM faces several disadvantages and limitations, mainly as result of the technical and conceptual factors involved in the Critical Path Analysis(CPA) process. The below list include few of the advantages and limitations of CPM: ^{[9] [13] [14]}

• CPM can become extremely complicated and the complexity increases as the scope and extent of big projects increase. The risk of making a mistake in the calculation of the critical path becomes very high. If projects are not well defined CPM can become ineffective and difficult to manage.
• Does not take scheduling of personnel and resource allocations into account.
• It requires software to monitor the plan in bulky and lengthy projects.
• Critical path of a big project has to be calculated carefully since it is not always clear. In big projects CPM takes longer to identify and monitor the critical path. In many cases the critical paths might change and past critical paths may no longer be valid. This requires that the managers have to constantly review the network diagram and identify the changes occurred over the time.
• CPM operates on the assumption that there is a precise known time that each activity in the project will take, but that is not always the case in real practice.
• The time estimates of CPM are not based on statistical analysis.
• CPM cannot be used as a dynamic controlling device.

Conclusion

References

1. ↑ BusinessDictionary. (2016). Critical Path. Retrieved September 8, 2016, from http://www.businessdictionary.com/definition/critical-path.html.
2. ↑ Webodia. (2016). Critical Path Method. Retrieved September 8, 2016, from http://www.webopedia.com/TERM/C/Critical_Path_Method.html.
3. ↑ Kielmas, M. (2016). History of the Critical Path Method. Retrieved September 8, 2016, from http://smallbusiness.chron.com/history-critical-path-method-55917.html.
4. ↑ Francis, D., Horine, G. & Tittel, E. (2008). The Relationship Between Project Lifecycle and Project Management Processes. Retrieved September 8, 2016, from http://flylib.com/books/en/2.466.1.51/1/.
5. ↑ Project Management Institute. (2000). A Guide to the Project Management Body of Knowledge. Pp. 4. Retrieved September 10, 2016, from http://www.cs.bilkent.edu.tr/~cagatay/cs413/PMBOK.pdf.
6. ↑ ^{6.0 6.1} Larson, E. W & Gray, C. F. (2011). Project Management, the managerial process. 5th edition, Pp. 3-10, 157-172. USA: NY. ISBN 978-0-07-340334-2.
7. ↑ Haughey, D. (2011). Understanding the projoect management triple constraint. Retrieved September 16, 2016, from https://www.projectsmart.co.uk/understanding-the-project-management-triple-constraint.php.
8. ↑ ProgramSucess. (2011). Scope, Time and Cost – Managing the Triple Constraint. Retrieved September 8, 2016, from https://programsuccess.wordpress.com/2011/05/02/scope-time-and-cost-managing-the-triple-constraint/.
9. ↑ ^{9.0 9.1} Stealth, P. & Roy, G. L. (2009). Project’s Analysis through CPM (Critical Path Method). Pp. 23-25. Retrieved September 8, 2016, from http://www.iiuedu.eu/press/journals/sds/sds1_july_2008/05_SECC_01.pdf.
10. ↑ Chung, E. (2016). Critical Path Method vs Critical Chain Method for PMP Exam. Retrieved September 5, 2016, from http://edward-designer.com/web/critical-path-method-vs-critical-chain-method-for-pmp-exam/.
11. ↑ Anderson, E. B. & Hales, S. T. (1986). Critical Path Method Applied to Research Project Planning: Fire Economics Evaluation System (FEES). Pp. 1-2. Retrieved September 8, 2016, from http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.115.6122&rep=rep1&type=pdf.
12. ↑ Advantages of Critical Path Method (CPM). Retrieved September 8, 2016, from http://theconstructor.org/construction/const-management/scheduling/advantages-of-critical-path-method-cpm/6873/.
13. ↑ Advantages and disadvantages in the implementation of CPM. Retrieved September 8, 2016, from http://www.cpmscheduling.com/critical-path-method/advantages-and-disadvantages-in-the-implementation-of-cpm.
14. ↑ Sinha, DK. (2015). Critical Path Method(CPM): Definition, Advantages and Limitations. Retrieved September 8, 2016, from http://www.yourarticlelibrary.com/business/planning-business/critical-path-method-cpm-definition-advantages-and-limitations/40754/.

Annotated Bibliography