# Program Evaluation and Review Technique (PERT) The Program Evaluation and Review Technique (PERT) is a project scheduling technique that models a project as a network of activities and events and accounts for uncertainty in how long each activity takes. It was developed in 1958 by the US Navy's Special Projects Office, with Lockheed and Booz Allen Hamilton, for the Polaris missile program. The method was described in a 1959 paper by Malcolm, Roseboom, Clark and Fazar in Operations Research. Instead of a single duration, PERT asks for three estimates per activity: - **Optimistic (o)**: the minimum time, if everything goes well - **Most likely (m)**: the best guess, if things proceed as normal - **Pessimistic (p)**: the maximum time, if everything goes wrong (excluding major catastrophes) The expected time is a weighted average: te = (o + 4m + p) / 6. Summing expected times along a path gives the expected duration of that path. PERT and the [[Critical Path Method (CPM)]] are complementary and often combined: CPM uses one time estimate per activity, PERT uses three. The three-point estimate is also used on its own, outside full PERT networks, as a quick way to make the uncertainty in an estimate visible. ## Memories I fondly remember learning this technique during my IT studies. At first it seemed theoretical, but when I first started working as a project manager, I finally felt the value of this approach. Even if I don't apply it manually, I still like to create reverse plannings, going from the target date back to now and identifying the critical path (cfr [[Critical Path Method (CPM)]]) and understanding what to pay attention to, where to put emphasis/priorities etc. ## References - https://en.wikipedia.org/wiki/Program_evaluation_and_review_technique - D. G. Malcolm, J. H. Roseboom, C. E. Clark, W. Fazar, "Application of a Technique for Research and Development Program Evaluation", Operations Research, 1959: https://doi.org/10.1287/opre.7.5.646 - https://concepts.dsebastien.net/concept/three-point-estimation/ ## Related - [[Critical Path Method (CPM)]] - [[Work Breakdown Structure (WBS)]] - [[Task Weights]] - [[Hofstadter's Law]] - [[Directed Acyclic Graphs (DAG)]] - [[Project Management (MoC)]]