When to use it
Use it when a single estimate would conceal a meaningful range and estimators can explain the scenarios.
Do not interpret the weighted mean as a confidence date or assume the range is statistically calibrated.
- Define the scope, status date and units before collecting the inputs.
- Substitute the values into the formula and retain their units.
- Interpret the result against the assumptions and decide what evidence or action is needed next.
Formula & inputs
O ≤ M ≤ P, in the same units and for the same scope. A triangular mean instead gives equal weight to all three inputs.
Worked example
A work package is estimated at four days in an optimistic case, seven days most likely, and sixteen days in a pessimistic case.
The different means come from different distribution assumptions. Discuss why the upper case is long and what evidence could narrow the uncertainty.
Common pitfall
Correlated delays and resource contention are not captured by simply adding activity means.
Source & related material
Standard quantitative technique; this explanation is by fannarmaximus. No single inventor is claimed. The arithmetic is computed from explicit inputs, not copied from an official sample question.