PERT

PERT, or Program Evaluation and Review Technique, is a project management method used to analyze and represent the tasks involved in completing a project, with an emphasis on time uncertainty. It uses a network diagram of activities and their dependencies to help plan, schedule, and coordinate complex projects.

The technique originated in the 1950s for the U.S. Navy’s Polaris missile program, with involvement from management consultants and contractors. It was developed to handle the inherent uncertainty in large, intricate projects and to provide a probabilistic view of completion times. PERT contrasts with single-point time estimates by incorporating multiple time scenarios for each activity.

In PERT, each activity is assigned three time estimates: optimistic (O), most likely (M), and pessimistic (P). The expected duration Te for an activity is calculated as Te = (O + 4M + P) / 6, and the activity’s standard deviation is (P − O) / 6. The network is analyzed to identify the critical path, the sequence of activities with the longest total expected duration, which determines the project’s overall estimated completion time. A probability can be assigned to meeting a target date by considering the distribution of total project duration along the network, often using the central limit theorem as an approximation.

Benefits of PERT include improved schedule reliability, better risk assessment, and a clear view of task dependencies. Limitations involve the quality of input estimates, potential complexity for large networks, and assumptions of activity independence and normal-like distributions. While many projects now employ more integrated techniques, PERT remains a foundational approach in project planning and risk analysis, frequently used in conjunction with CPM and modern project management tools.