PERTDiagramme

PERT diagram, short for Program Evaluation and Review Technique, is a project management tool used to plan and schedule complex projects by focusing on time and uncertainty. It represents a project as a network of activities and milestones, helping managers identify the sequence of tasks, parallel work, and the critical path where delays directly affect the project end date. PERT diagrams can be drawn in two common forms: activity-on-node (AON) and activity-on-arrow (AOA), allowing flexibility in how activities and dependencies are depicted.

A hallmark of PERT is the use of probabilistic time estimates. For each activity, three time estimates are recorded: optimistic (a), most likely (m), and pessimistic (b). The expected time is calculated as TE = (a + 4m + b) / 6, and the variance as Var = ((b − a) / 6)². These inputs enable probabilistic analysis of the project’s duration and help compute the likelihood of meeting a target completion date, often assuming a normal distribution for total duration.

How PERT is used: identify activities and dependencies, estimate time with three-point data, construct the network, determine earliest and latest start/finish times, and identify the critical path—the sequence of activities with zero total slack. The critical path indicates the minimum project duration and where management attention is required. PERT is frequently used in research, defense, construction, and software projects, especially where task durations are uncertain.

Limitations include the reliance on accurate time estimates and the potential complexity for large projects; PERT does not inherently optimize resource allocation. It is often used alongside other methods like the Critical Path Method and Gantt charts.