Introducing Statistical PERT
In the 21st 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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