The program evaluation and review technique (PERT) identifies every task involved in a project, the time required to complete each one, and the dependencies between tasks. The result is a network diagram that clarifies where the critical path is located in a project. The critical path is that sequence of tasks that requires the longest total time period to complete. There may be several paths within a PERT chart, each comprised of a different set of interrelated tasks that must be completed. Whichever path has the longest duration is the critical path, since shrinking this path will compress the duration of the entire project.
The critical path must be closely monitored to ensure that a project is completed in a timely manner. If a task on the critical path is delayed, this also delays the entire project. A remedial action is to overload tasks on the critical path with additional resources.
PERT allows for the inclusion of variable amounts of time for each task. Thus, each task has a most likely, pessimistic, and optimistic duration attached to it. These three estimates are then combined to arrive at a single estimated duration for each task. This probability feature means that PERT is especially useful when dealing with projects for which there is some uncertainty about completion dates.
The main problem with PERT is the large amount of data that must be incorporated into the planning process. This makes it expensive to maintain, which usually limits its usefulness to larger and more complex projects.