Programme Evaluation and Review Techniques (PERT)

Program Evaluation and Review Technique (PERT) is a method used to examine the tasked that are in a schedule and determine a variation of the Critical Path Method (CPM). It analyzes the time required to complete each task and its associated dependencies to determine the minimum time to complete a project. It estimates the shortest possible time each activity will take, the most likely length of time, and the longest time that might be taken if the activity takes longer than expected.  

The method was developed by the US Navy in 1957 on the Polaris nuclear submarine project.
To conduct PERT Analysis, three time estimates are obtained (optimistic, pessimistic, and most likely) for every activity along the Critical Path. Then use those estimates in the formula below to calculate how much time for each project stage:

Formula: (P+4M+O)/6

• Optimistic Time (O): The minimum possible time required to accomplish a task, assuming everything proceeds better than is normally expected.
• Pessimistic Time (P): The maximum possible time required to accomplish a task, assuming everything goes wrong (excluding major catastrophes).
• Most likely Time (M): The best estimate of the time required to accomplish a task, assuming everything proceeds as normal.

Example of the three time estimates

Example of a Critical Path Nodal Diagram

PERT Analysis can be conducted using Microsoft Project.