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Program Evaluation and Review Technique work is represented in a chart or diagram that makes visible all scheduled tasks in a project in sequence. Using PERT, project managers analyze how much time it will take to complete each task and any dependent task, and then forecast how long the whole project will last. 

While most project frameworks depend on forecasting the most likely timeline, PERT integrates three time scenarios – the shortest possible time, the most likely time, and the longest possible time. PERT’s formulas come up with a weighted average of those three durations, resulting in an estimate that is often more accurate than other models.

The Birth of PERT
PERT was born during the Cold War when the U.S. Navy undertook the Polaris missile project to arm nuclear submarines. This effort required coordinating some 9,000 subcontractors as well as dozens of simultaneous and interdependent activities. Worried about the Soviet threat, the Navy wanted to deliver the project as rapidly as possible. 

Navy officials worked with defense contractor Lockheed and consultants Booz, Allen, and Hamilton to design a program tool that would ensure the missiles were ready when the submarines were. They originally sketched the concepts on a tablecloth over lunch, and eventually they evolved into PERT.

Due in large part to PERT, Polaris finished years ahead of schedule and on budget, and it was hailed as a U.S. triumph in the arms race. As a result, the technique became standard on large government projects of that era. Contractors who worked on those projects (especially in defense and construction) helped spread it to the private sector, according to Helen Cooke, Project Management Consultant and co-author of the textbook The McGraw-Hill 36-Hour Course: Project Management.

“The government required contractors to use it on complex projects in defense and construction. That caused PERT to proliferate in the private sector, and it was adopted heavily by project managers,” Cooke said. 

Mitchell L. Springer, Executive Director of Purdue University’s Polytechnic Institute, said in his book Program Management: A Comprehensive Overview of the Discipline that PERT experienced a rapid rise and then an abrupt decline in use in the 1970s. This is attributed to two factors: PERT was over-applied and combined with non-scheduling data that made it cumbersome to work with. However, Springer said the rise of software programs to run PERT prompted a resurgence in the 2000s.