Practical ranges for schedule risk

If you are dealing with a set of estimate ranges

Estimating the very highest and very lowest
- E.g. the shortest time for an activity with 0% probability
- Or the maximum time with 100% probability
Does not make sense
- So, don't be misled
Seek to establish optimistic and pessimistic estimates
- At the 5% and 95% points respectively
- Equivalent to -1.6 SD to +1.6 SD = 3.2 SDs