Don’t ask “How long will this task take?” because the customary response will be the “most likely” estimate without considerations for the best-case and worst-case scenarios.
A staff may pad a two-day task to 2.5 days “just to be safe.” His team leader may add a day for “good measure” with the manager “blindly” tacking another 10-15% contingency. With this nonsense, the final estimate can easily become 100% more than the original!
It is better to ask for raw optimistic (O), most likely (M) and pessimistic (P) estimates—along with the assumptions. Manage the project based on the “weighted” expected (E) estimates with a contingency of ± three standard deviations (±3S). If the standard deviation is too wide, scrutinize the assumptions and revise the estimates.
E = (O + 4M + P) / 6
S = (P – O) / 6
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Use three-point estimates to make contingency reserves more accurate
