Duration estimation is the process of predicting how long each activity in a project will take. The accuracy of duration estimates directly impacts project success.
1. Estimating Techniques:
Several techniques are used to estimate durations, including:
- Analogous Estimating: Uses historical data from similar projects.
- Parametric Estimating: Uses mathematical relationships between historical data and project variables.
- Three-Point Estimating: Accounts for uncertainty by using three estimates:
- Optimistic (O): Best-case scenario
- Pessimistic (P): Worst-case scenario
- Most Likely (M): The most probable outcome
Formula for Three-Point Estimating:
- Expected Duration (ED) = (O + 4M + P) / 6
2. Example: Three-Point Estimating
Consider an activity with the following estimates:
- Optimistic Estimate (O) = 4 days
- Most Likely Estimate (M) = 6 days
- Pessimistic Estimate (P) = 8 days
Using the formula:
- ED = (4 + 4×6 + 8) / 6 = (4 + 24 + 8) / 6 = 36 / 6 = 6 days
Thus, the expected duration for the task is 6 days.
3. Risk Buffers
Once durations are estimated, it’s important to add contingency buffers to account for risks. One method is to use a Risk Factor and multiply it by the estimated duration:
- Contingency = Estimated Duration × Risk Factor
Example:
- Estimated Duration = 10 days
- Risk Factor = 0.15 (15% buffer)
- Contingency = 10 × 0.15 = 1.5 days
Thus, the final duration estimate is:
- 10 + 1.5 = 11.5 days
4. Benefits of Accurate Duration Estimating
By using these methods, project managers can develop more accurate schedules, reduce risk of delays, and ensure that resources are allocated efficiently.