Project activities must have an accurate time estimate before any work is executed. This must be prepared whether using a flexible Agile or traditional Waterfall approach. The lack of Time and Duration estimates will impact our “Time is Money” theme. Developing an estimate, even for small projects, can be a complex task. Using the PERT (Program Evaluation and Review Technique) method for estimating is considered one of the more successful and proven techniques. Apply the estimate to the project schedule.
The following PERT estimates are considered:
- Most Optimistic amount of Time to finish (OT)
- Most Likely amount of Time to finish (LT)
- Most Pessimistic amount of Time to finish (PT)
Using these three estimates we can calculate the “Expected Time (ET)” to finish
ET = (OT + 4 * LT + PT)/6
Using the same estimates the possible “Variance Time (VT)” may be calculated, sometimes used as the contingent time estimate
VT = (PT – OT)2 / 62