Introducing Statistical PERT

William lives and works as an IT project manager in South Florida, and is a member of the South Florida chapter of PMI. He created StatisticalPERT.com.

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Topics: Estimating, Risk Management, Schedule Management, Scheduling

In the 21^st century, why are some of us still using the Program Evaluation Review Technique (PERT) to create project estimates? PERT was created by the U.S. Navy in the 1950s--a time before Microsoft Excel existed and even before personal computers existed.

As project management has grown into a full-fledged profession, we still require aspiring PMP exam takers to have a rudimentary knowledge of PERT and the most common PERT formula for creating a risk-adjusted estimate:

[Optimistic + (4 x Most Likely) + Pessimistic] / 6

Beyond just having knowledge of PERT estimation, some project managers actually use PERT (or a variant) to create estimates for work effort, task duration and/or project-related costs.

PERT does offer benefits to project managers. That’s why A Guide to the Project Management Body of Knowledge (PMBOK Guide) still mentions it. It’s easy to create PERT estimates using a three-point estimate for optimistic, most likely and pessimistic outcomes. It’s quick, too, and you don’t even need a spreadsheet. It arguably makes planning more accurate, because it creates risk-adjusted estimates that place more weight on a “most likely” outcome, while also factoring in best-case and worst-case scenarios, too.

Monte Carlo simulation offers a lot more value to project managers than using PERT, because it executes a project …

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