The Critical Chain Method - Revision history

Tkokotas at 15:45, 18 December 2018

2018-12-18T15:45:12Z

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	~~[[Category:Project Management]][[Category:Scheduling]][[Category:Uncertainty]][[Category:Theory of Constraints]]~~		''Developed by Fabio Labrini''
	* If there are any problems in finding the article with the excel list, is because I changed the title.

	The Critical Chain method in Project Management(CCPM) is a method to plan, execute, manage, and control both single and multi projects, which emphasizes the effects of resource allocation and activity duration uncertainty.		The Critical Chain method in Project Management(CCPM) is a method to plan, execute, manage, and control both single and multi projects, which emphasizes the effects of resource allocation and activity duration uncertainty.
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	= References =		= References =
	<References/>		<References/>
			[[Category:Project Management]][[Category:Scheduling]][[Category:Uncertainty]][[Category:Theory of Constraints]]

F.labrini at 23:19, 28 September 2015

2015-09-28T23:19:42Z

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	[[Category:Project Management]][[Category:Scheduling]][[Category:Uncertainty]][[Category:Theory of Constraints]]		[[Category:Project Management]][[Category:Scheduling]][[Category:Uncertainty]][[Category:Theory of Constraints]]
			* If there are any problems in finding the article with the excel list, is because I changed the title.

	The Critical Chain method in Project Management(CCPM) is a method to plan, execute, manage, and control both single and multi projects, which emphasizes the effects of resource allocation and activity duration uncertainty.		The Critical Chain method in Project Management(CCPM) is a method to plan, execute, manage, and control both single and multi projects, which emphasizes the effects of resource allocation and activity duration uncertainty.
	It has demonstrated over the past 10 years its ability to significantly reduce the duration of projects, to ensure that projects are completed on time, and to increase resource productivity.<ref name="FR">Marris P., (2011), ''La chaîne critique pour réduire le time to market et accroître la productivité'', STP PHARMA PRATIQUES vol.21 N°5</ref>.		It has demonstrated over the past 10 years its ability to significantly reduce the duration of projects, to ensure that projects are completed on time, and to increase resource productivity.<ref name="FR">Marris P., (2011), ''La chaîne critique pour réduire le time to market et accroître la productivité'', STP PHARMA PRATIQUES vol.21 N°5</ref>.

F.labrini: /* TOC to Project Management */

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TOC to Project Management

F.labrini: /* Limitations */

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Limitations

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	It has been argued that experienced project managers have known the principles behind CCPM for decades, and CCPM’s uniqueness is in the terminology rather than in its substance<ref name="Clook"></ref>.		It has been argued that experienced project managers have known the principles behind CCPM for decades, and CCPM’s uniqueness is in the terminology rather than in its substance<ref name="Clook"></ref>.

	Firstly, one of the main critique regards the CCPM indication of reducing the task duration estimates by a specific percentage, “which seems arbitrary”<ref name=”MIT”> S.C. Cook, (1998) ''Applying critical chain to improve the management of uncertainty in project'', MS thesis, Massachusetts Institute of Technology, USA</ref>.		Firstly, one of the main critique regards the CCPM, is the indication of reducing the task duration estimates by a specific percentage, “which seems arbitrary”<ref name=”MIT”> S.C. Cook, (1998) ''Applying critical chain to improve the management of uncertainty in project'', MS thesis, Massachusetts Institute of Technology, USA</ref>.
	The method, by suggesting this fixed reduction, assumes that all resources overestimate task duration by the same amount. The latter it is not true since the amount overestimated depends on the individual and it is based on personality, job experience, nature of the task, workload, or other reasons<ref name="Clook"></ref>.		The method, by suggesting this fixed reduction, assumes that all resources overestimate task duration by the same amount. The latter it is not true since the amount overestimated depends on the individual and it is based on personality, job experience, nature of the task, workload, or other reasons<ref name="Clook"></ref>.
	Furthermore, resources who know that their estimates will be reduced could be motivated to increase or double the estimates. By doing so, they still have their safety margins even after the reduction.		Furthermore, resources who know that their estimates will be reduced could be motivated to increase or double the estimates. By doing so, they still have their safety margins even after the reduction.

	Secondly, while an advantage of CCPM is creating a schedule that considers resource availability, actually the mathematical problem of creating a precedence and resource dependent schedule is a well known NP-hard problem<ref> Wuliang P, Minli J., (2009), ''A Revised Critical Chain Method and Optimization Model'', Applied Mechanics and Materials vols. 16-19, pp. 426-430</ref>. It means that there are no efficient algorithms for finding optimal schedule for large project. Consequently, heuristic rules, which generate solution that are hoped to be close to optimum~~, are used~~<ref name="Clook"></ref>.		Secondly, while an advantage of CCPM is creating a schedule that considers resource availability, actually the mathematical problem of creating a precedence and resource dependent schedule is a well known [https://en.wikipedia.org/wiki/NP-hardness NP-hard problem]<ref> Wuliang P, Minli J., (2009), ''A Revised Critical Chain Method and Optimization Model'', Applied Mechanics and Materials vols. 16-19, pp. 426-430</ref>. It means that there are no efficient algorithms for finding optimal schedule for large project. Consequently, heuristic rules are used, which generate solution that are hoped to be close to optimum<ref name="Clook"></ref>.

	Thirdly, CCPM involves the elimination of multitasking as a way to improve performance. However, a study of 64 high technology firms conducted by McCollum and Sherman (1991)<ref> McCollum, J.K., & Sherman, J.D., (1991), ''The effects of matrix organization size and number of project assignments on performance'', IEEE Transactions on Engineering Management vol.38, pp.75-78</ref> found that there is a relationship between the number of projects assigned to R&D personnel and key performance of the company. They found that assignment of two projects is the optimal number, and until three projects no problems occurred.		Thirdly, CCPM involves the elimination of multitasking as a way to improve performance. However, a study of 64 high technology firms conducted by McCollum and Sherman (1991)<ref> McCollum, J.K., & Sherman, J.D., (1991), ''The effects of matrix organization size and number of project assignments on performance'', IEEE Transactions on Engineering Management vol.38, pp.75-78</ref> found that there is a relationship between the number of projects assigned to R&D personnel and key performance of the company. They found that assignment of two projects is the optimal number, and until three projects no problems occurred.
	This study alone cannot confirm that the optimal number, in regards to performance, of project assigned to one individual is two, since it was just conducted in R&D environment. Further studies are necessary.		This study alone cannot confirm that the optimal number, in regards to performance, of project assigned to one individual is two, since it was just conducted in R&D environment. Further studies are necessary.

	Finally, another criticism is about the adoption of CCPM. A company that ~~want~~ to adopt the CCPM has to incur in two big expenses: provide training to various levels of the organization, and purchase the proper softwares. In order to be efficient, CCPM requires training to change organizational culture about: giving up ownership of the task duration and relying on the schedule buffer to absorb deviation, replacing the concept of due date with estimated completion date range(represented by Feeding and Project Buffers), and avoiding multitasking<ref name="Clook"></ref>.		Finally, another criticism is about the adoption of CCPM. A company that wants to adopt the CCPM has to incur in two big expenses: provide training to various levels of the organization, and purchase the proper softwares. In order to be efficient, CCPM requires training to change organizational culture about: giving up ownership of the task duration and relying on the schedule buffer to absorb deviation, replacing the concept of due date with estimated completion date range(represented by Feeding and Project Buffers), and avoiding multitasking<ref name="Clook"></ref>.

	= Suggested resources =		= Suggested resources =

F.labrini: /* Benefits */

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Benefits

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	The following are some of the advantages or differences from traditional scheduling methods which mainly caracterize CCPM.		The following are some of the advantages or differences from traditional scheduling methods which mainly caracterize CCPM.
	Those include: accounting the uncertainty in duration by explicating the buffer and sharing its size with all the people involved in a project(workers, management, stakeholders), considering the resource availability and scheduling consequently, providing a clear overview of the project status and visibility of threats while allowing for intervention.		Those include: accounting the uncertainty in duration by explicating the buffer and sharing its size with all the people involved in a project(workers, management, stakeholders), considering the resource availability and scheduling consequently, providing a clear overview of the project status and visibility of threats while allowing for intervention. All leading to respect the end due date.

	== Limitations ==		== Limitations ==

F.labrini: /* Benefits */

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Benefits

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	All projects that have properly applied the methodology have completed the project under the original time estimate, fulfilled the original scope, and came in near or under the estimated budget. Project durations normally reduce by at least 50% in the first pass, and several companies have taken the early successes to cause further substantial reductions in project duration <ref name="CCPMPer"></ref>.		All projects that have properly applied the methodology have completed the project under the original time estimate, fulfilled the original scope, and came in near or under the estimated budget. Project durations normally reduce by at least 50% in the first pass, and several companies have taken the early successes to cause further substantial reductions in project duration <ref name="CCPMPer"></ref>.

	The following companies have implemented the CCPM with positive results: Israeli Aircraft Industry, US Air Force, Johnson & Johnson, Procter & Gamble, Ely Lilly Boeing, ITT, BAE System, and Harris<ref name="CCPMPer"></ref><ref name="IOWA">Kirpes C, ''Evaluating the Use of Scheduling Techniques: Critical Chain Project Management’’, Proceedings of the 2014 Industrial and Systems Engineering Research Conference</ref><ref name="FR"></ref>. However, the result obtained are not only attributable to the CCPM but also to the quality of the actor involved, and to the weak starting situation ~~of company~~.		The following companies have implemented the CCPM with positive results: Israeli Aircraft Industry, US Air Force, Johnson & Johnson, Procter & Gamble, Ely Lilly Boeing, ITT, BAE System, and Harris<ref name="CCPMPer"></ref><ref name="IOWA">Kirpes C, ''Evaluating the Use of Scheduling Techniques: Critical Chain Project Management’’, Proceedings of the 2014 Industrial and Systems Engineering Research Conference</ref><ref name="FR"></ref>. However, the result obtained are not only attributable to the CCPM but also to the quality of the actor involved, and to the weak starting situation in some cases.

	The following are some of the advantages or differences from traditional scheduling methods which mainly caracterize CCPM.		The following are some of the advantages or differences from traditional scheduling methods which mainly caracterize CCPM.

F.labrini: /* Planning */

2015-09-28T22:57:09Z

Planning

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	===Planning===		===Planning===
	[[File:Project_buffer.PNG\|400px\| thumb\| \|'''Figure 8:''' Transfer of the task level safety to the project level.]]		[[File:Project_buffer.PNG\|400px\| thumb\| \|'''Figure 8:''' Transfer of the task level safety to the project level.]]
	~~1. the~~ first step in order to apply CCPM consists in defining an initial schedule taking in consideration task duration estimates and dependencies. In other words, the initial schedule could be also defined as the “infinite capacity schedule” since the resource availability is not considered yet.		The first step in order to apply CCPM consists in defining an initial schedule taking in consideration task duration estimates and dependencies. In other words, the initial schedule could be also defined as the “infinite capacity schedule” since the resource availability is not considered yet.

	2. the schedule must be adjusted by positioning the tasks according to the capacity and availability of the resources. Because at least some of the resources have limited availability, the resulting schedule is likely to be longer than the schedule obtained with the basic Critical Path Method, as critical activities are delayed while waiting for the resources they require<ref name="Clook"> Raz T., Barnes R., Dvir D., (2003), ''A critical look at critical chain project management'', Project Management Journal, vol. 34</ref>.		Thereafter, the schedule must be adjusted by positioning the tasks according to the capacity and availability of the resources. Because at least some of the resources have limited availability, the resulting schedule is likely to be longer than the schedule obtained with the basic Critical Path Method, as critical activities are delayed while waiting for the resources they require<ref name="Clook"> Raz T., Barnes R., Dvir D., (2003), ''A critical look at critical chain project management'', Project Management Journal, vol. 34</ref>.

	3. the longest sequence of activities needed to complete the project taking into account both the interdependencies and resource capacity is defined as the Critical Chain.		Now, the longest sequence of activities needed to complete the project taking into account both the interdependencies and resource capacity is defined as the Critical Chain.

			Next step involves shortening duration estimates, removing the safety margin from each critical task and pooling them together at the PB. The latter is place at the end of the project, and represented as a task.

	4. this step involves shortening duration estimates, removing the safety margin from each critical task and pooling them together at the PB. The latter is place at the end of the project, and represented as a task.
	Then, the same process of grouping safety margins is applied to the non-critical paths. The safety margins of each non-critical path are grouped into a FB placed where the path merges into the critical chain path.		Then, the same process of grouping safety margins is applied to the non-critical paths. The safety margins of each non-critical path are grouped into a FB placed where the path merges into the critical chain path.

F.labrini: /* Planning */

2015-09-28T22:54:15Z

Planning

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	===Planning===		===Planning===
	[[File:Project_buffer.PNG\|400px\| thumb\| \|'''Figure 8:''' Transfer of the task level safety to the project level.]]		[[File:Project_buffer.PNG\|400px\| thumb\| \|'''Figure 8:''' Transfer of the task level safety to the project level.]]
	~~The~~ first step in order to apply CCPM consists in defining an initial schedule taking in consideration task duration estimates and dependencies. In other words, the initial schedule could be also defined as the “infinite capacity schedule” since the resource availability is not considered yet.		1. the first step in order to apply CCPM consists in defining an initial schedule taking in consideration task duration estimates and dependencies. In other words, the initial schedule could be also defined as the “infinite capacity schedule” since the resource availability is not considered yet.
	~~Thereafter,~~ the schedule must be adjusted by positioning the tasks according to the capacity and availability of the resources. Because at least some of the resources have limited availability, the resulting schedule is likely to be longer than the schedule obtained with the basic Critical Path Method, as critical activities are delayed while waiting for the resources they require<ref name="Clook"> Raz T., Barnes R., Dvir D., (2003), ''A critical look at critical chain project management'', Project Management Journal, vol. 34</ref>. ~~Then,~~ the longest sequence of activities needed to complete the project taking into account both the interdependencies and resource capacity is defined as the Critical Chain.
	~~Next~~ step involves shortening duration estimates, removing the safety margin from each critical task and pooling them together at the PB. The latter is place at the end of the project, and represented as a task.		2. the schedule must be adjusted by positioning the tasks according to the capacity and availability of the resources. Because at least some of the resources have limited availability, the resulting schedule is likely to be longer than the schedule obtained with the basic Critical Path Method, as critical activities are delayed while waiting for the resources they require<ref name="Clook"> Raz T., Barnes R., Dvir D., (2003), ''A critical look at critical chain project management'', Project Management Journal, vol. 34</ref>.

			3. the longest sequence of activities needed to complete the project taking into account both the interdependencies and resource capacity is defined as the Critical Chain.

			4. this step involves shortening duration estimates, removing the safety margin from each critical task and pooling them together at the PB. The latter is place at the end of the project, and represented as a task.
	Then, the same process of grouping safety margins is applied to the non-critical paths. The safety margins of each non-critical path are grouped into a FB placed where the path merges into the critical chain path.		Then, the same process of grouping safety margins is applied to the non-critical paths. The safety margins of each non-critical path are grouped into a FB placed where the path merges into the critical chain path.

F.labrini: /* 3. Subordinate everything else to the above decision */

2015-09-28T22:48:49Z

3. Subordinate everything else to the above decision

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	''' Subordinate Merging Paths '''		''' Subordinate Merging Paths '''


	To protect the critical chain from potential delays by subordinating critical chain feeding paths, CCPM places an aggregate FB on each path that feeds the critical chain<ref name="CCPM2"></ref>. In addition, the FB acts as means to measure and control the feeding paths.		To protect the critical chain from potential delays by subordinating critical chain feeding paths, CCPM places an aggregate FB on each path that feeds the critical chain<ref name="CCPM2"></ref>. In addition, the FB acts as means to measure and control the feeding paths.

F.labrini: /* 2. Decide how to exploit the project’s constraints */

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2. Decide how to exploit the project’s constraints

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	As stated previously, usually task duration estimates are determined with a probability of completion around 90%.		As stated previously, usually task duration estimates are determined with a probability of completion around 90%.
	In order to minimize the negative resource behavior and to avoid wasting the contingency allocated to the single tasks, CCPM entails to remove the safety time from the task estimates and shorten them down to 50% of probability.		In order to minimize the negative resource behavior and to avoid wasting the contingency allocated to the single tasks, CCPM entails to remove the safety time from the task estimates and shorten them down to 50% of probability.
	Contingency is the difference between a 50% probable estimate and a 90% probable estimate<ref name="CCPM2"></ref>.		Contingency equals the difference between a 50% probable estimate and a 90% probable estimate<ref name="CCPM2"></ref>.
	Critical Chain method requires that the schedule be built with only the time to do the work without any safety. This is the time we expect the work to take if allowed to focus a full sustainable level of effort on it and if there are no significant problems<ref name=”frank”> Patrick S.F., (1999), ''Critical chain scheduling and buffer management - getting out from between Parkinson’s rock and Murphy’s hard place'', PM Network 13, pp. 57-62</ref>		Critical Chain method requires that the schedule be built with only the time to do the work without any safety. This is the time we expect the work to take if allowed to focus a full sustainable level of effort on it and if there are no significant problems<ref name=”frank”> Patrick S.F., (1999), ''Critical chain scheduling and buffer management - getting out from between Parkinson’s rock and Murphy’s hard place'', PM Network 13, pp. 57-62</ref>

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	In order to apply the five steps, it is necessary at first to define the goal of a project. The primary goal of a project is considered to be the promised project due date.		In order to apply the five steps, it is necessary at first to define the goal of a project. The primary goal of a project is considered to be the promised project due date.

	===1. ~~'''~~Identify project’s constraint~~'''~~===		===1. Identify project’s constraint===
	According to the TOC, the part of the system that constrains the objective is the ''Critical Chain'', which is defined as “the longest chain of precedence and resource dependent tasks that determines the overall duration of a project”. Defining the constraint of a project in		According to the TOC, the part of the system that constrains the objective is the ''Critical Chain'', which is defined as “the longest chain of precedence and resource dependent tasks that determines the overall duration of a project”. Defining the constraint of a project in
	terms of the schedule derives from the impact that schedule has on project cost and project scope. The three conditions are dependent<ref name="CCPMPer">Larry P. Leach, (1997), ''Critical Chain Project Management Improves Project Performance'', Advanced Projects Institute</ref>.		terms of the schedule derives from the impact that schedule has on project cost and project scope. The three conditions are dependent<ref name="CCPMPer">Larry P. Leach, (1997), ''Critical Chain Project Management Improves Project Performance'', Advanced Projects Institute</ref>.
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	and Critical Chain would be identical.		and Critical Chain would be identical.

	===2. ~~'''~~Decide how to exploit the project’s constraints~~'''~~===		===2. Decide how to exploit the project’s constraints===
	[[File:Estimate_distribution.PNG\|400\| thumb\| \|'''Figure6:''' Typical probability distribution for a task with uncertain distribution.]]		[[File:Estimate_distribution.PNG\|400\| thumb\| \|'''Figure6:''' Typical probability distribution for a task with uncertain distribution.]]
	This step can be translated in focusing on the activities of the Critical Chain to ensure efficient performance and no delays. In order to		This step can be translated in focusing on the activities of the Critical Chain to ensure efficient performance and no delays. In order to
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	The size of the PB is equal to the sum of the safety times removed from the task duration estimates of the tasks along the critical chain. The sizing of the FB follows the same procedure accounting for the tasks preceding the buffer.		The size of the PB is equal to the sum of the safety times removed from the task duration estimates of the tasks along the critical chain. The sizing of the FB follows the same procedure accounting for the tasks preceding the buffer.

	=== 3. ~~'''~~Subordinate everything else to the above decision~~'''~~===		=== 3. Subordinate everything else to the above decision===
	[[File:Feeding_bufferOK.PNG\|300px\| thumb\| \|'''Figure7:'''Feeding buffer absorbs delay from feeding paths.]]		[[File:Feeding_bufferOK.PNG\|300px\| thumb\| \|'''Figure7:'''Feeding buffer absorbs delay from feeding paths.]]
	Applied to project, it means that all the non-critical activities must not affect or delay any activity on the critical tasks.		Applied to project, it means that all the non-critical activities must not affect or delay any activity on the critical tasks.
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	CCPM also involves the late start of all activities in the feeding paths. This is done since the FB provides protection to the whole project from the non-critical path. The advantages of doing so are the following: reduce the impact of changes on work already performed, delay the project cash outlay, and give the project a chance to focus by starting with fewer simultaneous activity chains<ref name="CCPMPer"></ref>.		CCPM also involves the late start of all activities in the feeding paths. This is done since the FB provides protection to the whole project from the non-critical path. The advantages of doing so are the following: reduce the impact of changes on work already performed, delay the project cash outlay, and give the project a chance to focus by starting with fewer simultaneous activity chains<ref name="CCPMPer"></ref>.

	=== 4. ~~'''~~Elevate the project’s constraints~~'''~~ ===		=== 4. Elevate the project’s constraints ===
	When no more improvement can be obtained, this step suggests to invest in additional resources,		When no more improvement can be obtained, this step suggests to invest in additional resources,
	or increase the capacity of resources that can benefit most the critical chain performance.		or increase the capacity of resources that can benefit most the critical chain performance.
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	The elimination of task due dates, the encouragement of focusing on the task at hand, and the enforcement of a “Relay Runner” behavior contribute to increase the capacity of the resources. The latter is obtained by passing on early completion and avoiding multitasking.		The elimination of task due dates, the encouragement of focusing on the task at hand, and the enforcement of a “Relay Runner” behavior contribute to increase the capacity of the resources. The latter is obtained by passing on early completion and avoiding multitasking.

	=== 5. ~~'''~~If, as a result of the previous steps, the constraint has alleviated, return to Step 1~~'''~~ ===		=== 5. If, as a result of the previous steps, the constraint has alleviated, return to Step 1 ===

	== Critical Chain Method ==		== Critical Chain Method ==