What is simple average three-point activity duration estimate?
If you use a "simple" average estimate for a project, you would take a mean of all the 3 estimates i.e. add up all the 3 estimates and divide them by three.
Simple average Duration Estimate = (O + M + P) / 3
What is PERT?
Program Evaluation and Review Technique (PERT) is a type of "weighted" average duration estimation technique. If you use "weighted" average estimate for a project, you may give different weightage to the three estimates. PERT uses 1-4-1 weightage i.e. it gives 4 times more weightage to the Most Likely (M) estimate.
PERT Duration Estimate = (O + 4*M + P) / 6
SummaryPERT is a type of three-point estimation technique. PERT uses a "weighted" average estimate rather than a simple average. Three-point estimates are also used for Monte-Carlo Analysis.
Suggested Reading: It Takes Three to Make Good Estimates by Oliver F. Lehmann
Full 9-part series on Project Estimation and PERT
- Get Intimate with PERT
- The Power of Three in Project Estimation
- Three-point estimates vs PERT - What's the difference? (you are here)
- Say Hello to PERT
- The Magical Formula of PERT
- Probability and Statistics in Project Management
- PERT and CPM get Cozy
- PMP Quiz Contest - Activity Duration Estimates
- Standard Deviation and Project Duration Estimates
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