Program Evaluation and Review Technique (PERT)

Program Evaluation and Review Technique (PERT): A Comprehensive Guide

Introduction to PERT

Program Evaluation and Review Technique (PERT) is a statistical tool used in project management for analyzing and representing the tasks involved in completing a project. Developed by the U.S. Navy in the 1950s for the Polaris submarine missile program, PERT has become an essential scheduling methodology for complex projects.

Why PERT is Important

PERT is crucial in project management for several reasons:

• It helps manage uncertainty in project scheduling
• It identifies critical paths and potential bottlenecks
• It allows for realistic time estimations in complex projects
• It provides a visual representation of task dependencies
• It enables better resource allocation and risk management

What is PERT?

PERT is a statistical technique that analyzes the tasks involved in completing a project, especially the time needed to complete each task and the minimum time required to complete the total project. It's particularly useful in projects where activity times are uncertain.

PERT uses three time estimates for each activity:

• Optimistic time (O): The minimum possible time required
• Most likely time (M): The most probable time required
• Pessimistic time (P): The maximum possible time required

These three estimates are used to calculate the expected time (TE) using the formula:

TE = (O + 4M + P) ÷ 6

How PERT Works

1. Create a list of all activities required to complete the project
2. Determine dependencies between activities
3. Create a network diagram showing the sequence of activities
4. Estimate the three time values (O, M, P) for each activity
5. Calculate the expected time for each activity using the PERT formula
6. Identify the critical path, which represents the longest path through the network and determines the minimum project duration
7. Calculate slack for each activity to determine flexibility
8. Determine standard deviation to understand the uncertainty

Variance in PERT is calculated as: [(P - O)/6]²

PERT vs. CPM (Critical Path Method)

While often mentioned together, PERT and CPM have distinct differences:

• PERT uses probabilistic time estimates (three-point estimation)
• CPM uses deterministic time estimates (single-point estimation)
• PERT focuses on time management with uncertainty
• CPM balances time and cost and allows for time-cost trade-offs

Exam Tips: Answering Questions on PERT

1. Memorize the PERT formula: Know that TE = (O + 4M + P) ÷ 6 and be prepared to apply it

2. Understand variance calculation: Remember the formula [(P - O)/6]² to calculate variance

3. Know how to identify the critical path: The critical path is the longest path through the network and has zero float

4. Be clear on terminology:
• Float/Slack: Amount of time an activity can be delayed
• Forward Pass: Calculating early start and early finish times
• Backward Pass: Calculating late start and late finish times

5. Practice calculations: Be prepared for questions requiring numerical solutions

6. Distinguish PERT from other techniques: Know how PERT differs from CPM, Gantt charts, and other scheduling methods

7. Understand probability concepts: PERT assumes a beta distribution for time estimates

8. Application scenarios: Be ready to identify when PERT is most appropriate (complex projects with uncertain time estimates)

9. Network diagram interpretation: Practice reading and analyzing PERT network diagrams

10. Look for key phrases in exam questions such as "uncertain durations," "three-point estimation," or "probabilistic scheduling" that indicate PERT is the appropriate technique

PERT is an invaluable tool in the PMI-SP certification arsenal, particularly when dealing with projects that have significant uncertainty in activity durations. By understanding how to apply PERT effectively, project schedule professionals can better manage complex projects and more accurately predict completion times.