Introduction to PERT

What is PERT?

PERT was developed in the late 1950s by the U.S. Navy for the Polaris submarine missile program. It's particularly useful for projects where the duration of activities is uncertain.

Key Components of PERT

How to Create a PERT Chart

1. Identify Activities

   List all the activities required to complete the project. For each activity, identify immediate predecessor activities.

2. Determine Activity Sequence

   Establish the order in which activities must be performed. Some activities may be performed in parallel.

3. Estimate Activity Times

   For each activity, estimate three time durations:

   • Optimistic time (a): Minimum possible time required
   • Most likely time (m): Best estimate of time required
   • Pessimistic time (b): Maximum possible time required

   The expected time (te) is calculated using:
   te = (a + 4m + b) / 6

4. Construct the Network Diagram

   Draw the PERT chart with activities represented as arrows between nodes (events). The direction of arrows shows the sequence of activities.

   

   Example of a simple PERT chart

5. Identify the Critical Path

   Calculate the earliest and latest start and finish times for each activity. The critical path is the sequence of activities that has the longest duration and determines the project completion time.

6. Update as Project Progresses

   As the project progresses, update the PERT chart with actual times and revise estimates for remaining activities.

PERT Time Estimation Example

Advantages and Disadvantages of PERT

PERT vs. CPM

While PERT and CPM (Critical Path Method) are similar, there are key differences:

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