Critical Chain Method by Dr. Eliyahu M. Goldratt
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Critical Chain Method (CCM), developed by Dr. Eliyahu M. Goldratt (1997), is a schedule network analysis technique that takes account of task dependencies, limited resource availability & buffers. The first step is identifying a set of activities that results in the longest path to project completion which are called critical chains. As it includes resources into consideration, it may be longer than CPM schedule. Resources used in those critical chain activities are critical resources. Sets of activities that are in non-critical chain but converging to critical chain are feeders. Next step is shortening the project schedule by reducing the activity duration estimates with effective buffer management. CCM focuses on eliminating project schedule delays due to uncertainties, overestimation of task duration and wasted internal buffers.
The most difficult task that agonizes project managers is keeping project schedules on track. Because resources are restricted more and the highly skilled, high-priced resources are often required for multiple projects, resource constraints become one of the biggest risks to the project schedule. To help ensure that project schedules are met, project managers have learned to concentrate on the projects critical path. They also learned that the resources shared among projects, must be proactively managed.
The Critical Chain scheduling approach can be used to create “good” schedules that have provided substantial benefits in speed, predictability, and efficiency across many projects. The Critical Chain Scheduling includes a number of benefits that can be obtained by projects that make use of the approach. These include an aggressive target duration schedule, along with elimination of task due-dates, minimizes impact of “Parkinsons Law”. The second benefit is it allows buffer resources to focus on work without task due-date distraction and efficiently protect against “Murphys Law” with shorter project lead-times through concentrated safety protecting what is crucial to project success. Another benefit is resource alerts and effective prioritization of resource attention allow projects to take advantage of good luck and early task finishes while buffers protect against bad luck and later than scheduled finishes. Another benefit is buffer management which provides focus for schedule management, avoids unnecessary distraction, and allows recovery planning to take place when needed, but well before the project is in trouble.
There are additional benefits when the concepts that underlie it are expanded to multi-project environments. The use of buffers to prioritize resource attention will allow organizations to allow the focus on the task at hand to speed projects in the context of multi-project programs. The critical chain approach to single projects allows the multi-project environment to avoid the lead-time multiplying effect of multi-tasking.