The approach
Discuss distinct scenarios before calculating a weighted average. The explanation for the range is often more useful than the middle number.
- Define the same scope, completion condition and unit for every scenario.
- Elicit optimistic, most likely and pessimistic cases, stating what would make each occur.
- Choose a distribution assumption, calculate the mean and record the triggers for re-estimation.
Worked example
A work package has optimistic, most likely and pessimistic durations of 4, 7 and 16 days. The triangular mean is 9 days; the PERT-style mean is 8 days.
Try the inputs
Limits & next steps
A mean is not a commitment or percentile. Dependencies, shared resources and correlated uncertainty require a wider schedule analysis.
Source & further reading
This explanation and worked example are independently written. The linked publication provides context for the technique; it is not a licence to reuse its material.