What is Critical Chain?
Critical Chain Project Management (CCPM) is a methodology for planning, executing and managing projects in single and multi-project environments.
Critical Chain Project Management was developed by Dr Eli Goldratt and was first introduced to the market in his Theory of Constraints book “Critical Chain” in 1997. It was developed in response to many projects being dogged by poor performance manifested in longer than expected durations, frequently missed deadlines, increased costs in excess of budget, and substantially less deliverables than originally promised.
Problems with traditional project management
When planning for an upcoming project, estimates for task durations are required. In order for the plan to be treated as realistic, much time is spent ensuring estimates are accurate. Accurate estimates give us increased probability and high-confidence in the task completing on time. This allows additional safety time beyond the work content time required to be embedded within the task duration. The more safety in a task the more there is a tendency to behave in the following ways:
- Not starting the task until the last moment (Student Syndrome)
- Delaying (or pacing) completion of the task (Parkinson’s Law)
- Cherry picking tasks
As a result, the safety which was included at the planning stage is wasted and, if “Murphy” strikes and problems do occur, tasks over-run.
In addition Management force (for intuitive but invalid reasons) people to work on more than one task at once – creating multitasking. This drives people to switch between tasks leading them to elongate time estimates in planning and further waste the embedded task safety in execution.
Resources working on tasks also naturally resist reporting any early finishes. If an early finish is reported, the estimate for the task is recognised as too long. When a similar task on a different project is estimated, the initial response will be to again use a worst case duration. This will inevitably be challenged as the similar task was finished early last time. Increased pressure will be placed on the resource to accept a shorter estimate this time. The risk is that this, shorter estimate will not offer sufficient safety to the project should a problem occur. Hence resources ensure that sufficient safety is always embedded in each task estimate and the entire safety is used in execution of the task. This game is played by management and resources!
In summary, delays to tasks are passed on to the entire project however; benefits from tasks finishing early are rarely passed on to the same project.
The traditional tools used to manage projects; Critical Path Method (CPM), Program Evaluation and Review Technique (PERT), Gantt, Prince Etc. do not address the misuse of embedded safety and consequently the behaviours they drive.
Critical Chain Project Management
Critical Chain Project Management addresses these issues in the following ways.
Critical Chain - the Critical Chain is defined as the longest chain [not path] of dependent tasks. In this case, ‘dependent’ refers to resources and resource contention across tasks/projects as well as the sequence and logical dependencies of the tasks themselves. This differs from the Critical Path Method.
Estimations – To reduce the behaviours and time wasting associated with having too much embedded safety, Critical Chain Project Management recommends that task estimates are cut to half the length of a “normal” duration.
Safety – Critical Chain Project Management uses safety ‘Buffers’ to manage the impact of variation and uncertainty around projects. The safety at a task level is aggregated and moved to strategic points in the project flow. There are three types of buffer/strategic points necessary to ensure the project has sufficient safety:
- Project Buffer – A project buffer is inserted at the end of the project network between the last task and the completion date. Any delays on the longest chain of dependant tasks will consume some of the buffer but will leave the completion date unchanged and so protect the project. The project buffer is typically recommended to be half the size of the safety time taken out, resulting in a project that is planned to be 75% of a “traditional” project network.
- Feeding Buffers – delays on paths of tasks feeding into the longest chain can impact the project by delaying a subsequent task on the Critical Chain. To protect against this, feeding buffers are inserted between the last task on a feeding path and the Critical Chain. The feeding buffer is typically recommended to be half the size of the safety time taken out of the feeding path.
- Resource Buffers – Resource buffers can be set alongside of the Critical Chain to ensure that the appropriate people and skills are available to work on the Critical Chain tasks as soon as needed.
Priorities - All resources on a project are given clear and aligned priorities relating to the ‘health’ of the Critical Chain relative to its associated buffer and hence the project as a whole. A resource with more than one task open should normally be assigned to complete any task jeopardising any projects Critical Chain before completing any feeding path task.
Completion – resources on a task are encouraged to follow the ‘roadrunner’ approach. When there is work available it should be progressed at the fastest possible speed (without compromising quality) until completed. Tasks are not left partially complete to remove the temptation to multitask. As task duration estimates have reduced safety they drive resources to meet the more “aggressive” durations and limit the behaviours of Student Syndrome and Parkinson’s Law.
Buffer Management – the amount each buffer is consumed relative to project progress tells us how badly the delays are effecting our committed delivery date. If the variation throughout the project is uniform then the project should consume its project buffer at the same rate tasks are completed. The result is a project completed with the buffer fully consumed on the day it was estimated and committed. Project Managers determine the corrective actions necessary to ‘recover’ buffer time at points in the project where the buffer consumption is occurring faster than the project is progressing.
Remaining duration – tasks are monitored on their remaining duration, not their percentage complete. Resources report upon tasks in progress based on the number of days they estimate until the task will be complete. If the remaining duration stays static or increases, then Project Managers and Resource Managers “watching the buffers” know exactly where a blockage or potential delay is occurring and can take decisive action quickly to recover.
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