Project Management: Foundations to Practice · Schedule Management and the Critical Path Method
PERT and Handling Schedule Uncertainty
Developed for one of the most technically uncertain programs of its era, PERT tackles a problem CPM's original design does not: genuine uncertainty in how long a task will actually take.
The Program Evaluation and Review Technique, or PERT, was developed by the United States Navy in the late 1950s for the Polaris submarine missile program, a project involving significant uncertainty in how long individual tasks would actually take [17]. The Polaris program's combination of cutting-edge, previously unattempted engineering and enormous strategic stakes made traditional single-point scheduling estimates particularly unreliable, which directly motivated the development of a probabilistic alternative.
- PERT was developed for the Navy's Polaris submarine program, where task duration uncertainty was unusually high.
- PERT uses three estimates per activity (optimistic, most likely, pessimistic) combined via (O + 4M + P) / 6.
- PERT is most valuable for novel, R&D-style work where past data offers little guidance for single-point estimates.
- Modern tools often blend CPM's network logic with PERT's probabilistic estimating, sometimes extended with Monte Carlo simulation.