Operations Management: An Integrated Approach, 5th Edition

THE CRITICAL CHAIN APPROACH

Critical chain approach

Focus on the final due date that is based on the theory of constraints.

The critical chain approach is to get projects done faster and more consistently at or before the project due date. The focus is on the final due date rather than on individual activities or project milestones. The idea of the critical chain is that project activities are uncertain. Because of this uncertainty, we add safety time to project time estimates. In some cases, the safety time added exceeds 200 percent of the work time estimate.

Adding Safety Time

We have three ways to add safety time. First, we base time estimates on a pessimistic experience. Most time estimates include enough safety time to ensure that the project activity is completed on time 80 to 90 percent of the time. From statistics, we know that to cover 80 to 90 percent of the area under the curve, we have to add a substantial safety factor. Second, the more management levels involved, the greater the safety factor. Since no manager wants to look bad, we add more safety factors (perhaps an extra 10 to 20 percent). When each management level adds this safety factor, the total safety is greatly increased. Third, top management may make global reductions in project length. If we know that the total project length is likely to be reduced by 20 to 25 percent, we inflate our time estimate by 20 ...