PERT = Program Evaluation Review Technique

It is an estimation method developed by Booz Allen in the 1950s to support the Polaris Missle Project. The essence is that the project manager collects the pessimistic, most likely, and optimistic estimates and creates a weighted average: (P+O+4M)/6 for each project task. Summing them together gives the complete estimate. The standard deviation and variance associated with each task can be used to create a confidence interval which allows the final estimate to be quoted as a range. For example, 7 days +/- 3 days or $10 +/- $2.