Critical Chain Method (CCM) in Project Management
There are lots of project planning methods, tools and techniques available in the field of project time management. The Critical Chain Method is one of them which was introduced by Eliyahu M. Goldratt in his book “Critical Chain” in 1997. Unlike other books and guides for project management, Eliyahu M. Goldratt wrote his book as a novel. He provided real life examples to support his theory in Critical Chain (novel). According to him, the Critical Chain Method relies o the availability and levelling of resources required to complete the activities in order to complete the schedule.
In this article, we discuss the basic principles of Critical Chain Project Management and its practicality to managing projects.
Basics of the Critical Chain Method (CCM)
The Critical Path and the PERT methods have been used since 1960’s for the development of project schedules. As a project management tool, the Critical Chain Method differs from Critical Path and PERT methods. The Critical Path and PERT methods rely on task sequences and rules for creating work schedules.
However, this scheduling method relies on the theory of constraints which seeks to find the factor that limits achieving a goal. From this aspect, it is an alternative method to the standart and traditional methods.
The constraints that prevent to complete the project on time may include;
- Each task may involve uncertainty
- While making estimates for task durations, most of the time the team members increase the durations considering safety margins. So that most of the activities are overestimated.
After that, a resource-constrained critical path is determined which is altered from the original. Simply put, this method reviews the original critical path and creates a new schedule relying on the buffers.
Buffers in the Critical Chain Method (CCM)
This method considers the resource availabilities and their dependencies along all the task chain and adding buffers to the end of the chain. Unlike the critical path method, the critical chain method uses buffers instead of slacks (floats). This method defines three types of buffers.
Project buffer is placed at the end of the project between the last task and the project finish milestone. If there is a delay on the critical chain, this buffer will act as a contingency to prevent the delays.
There can be lots of non-critical chains in a network. Feeding Buffers are placed at the end of the non-critical chains to match the duration of critical chain. If there is a delay in the non-critical chain, this will not effect the critical chain.
As the project progresses, critical path changes and The Critical Chain should be recalculated. The Critical Chain method focuses on managing buffers in order to manage and control the project schedule effectively.
Differences Between The Critical Path and The Critical Chain
In The Critical Path Method, all the activities are sequenced in a network system and the critical path is determined by making mathematical calculations. There are no overall buffers added to the critical path but while estimating the activity durations implicit buffers are added to each activity in order to protect schedule from delays. This may result too much buffers added to the schedule and cause an uneffective schedule.
In The Critical Chain Method, activity durations are estimated by considering minimal time needed to perform the activity. A Project buffer is placed at the end of the project between the last task and the project finish milestone which acts as a contingency to prevent the project from delays. This will provide a higher efficiency for estimating activity durations and resource needs. By the use of this method a more aggressive and efficient schedule can be obtained.
Unlike The Critical Path Method, The Critical Chain Method considers both activity (task) and resource dependencies. Because The Critical Chain Method presumes that the quantity of resources are not unlimited.
In the Critical Chain Method, tracking the project performance by monitoring and controlling the consumption rate of the buffers is more important than tracking the project performance of individual activities. However Critical Path Method seeks to control the project performance by focusing on the activities.
According to the statistics and researches and only a few of the projects finish on time. Most of them completed after the planned finish date. The Critical Chain Method enables to develop a more effective and agressive schedule by using the outputs of The Critical Path Method. This method helps to optimize resources and activity durations for a flexible and realistic schedule. It can be useful to apply both critical path and critical chain methods while performing a schedule analysis. Because using both of them and comparing their results supports decision making within the project team.
In this article we make a short review of the Critical Chain Method. We hope that it will be useful for improving productivity and decision making within the project team.