PERT Estimates (Program Evaluation and Review Technique) are sometimes called 3-point estimates. The reason this technique is a best practice is that it gives you three benefits:
- Increased accuracy
- Useful information on the risks of each task that you estimate
- Better commitment from the project team members because the estimate considers the task’s risks.
How To Do PERT Estimates or 3-Point Estimates
1. You work with the team member assigned to the task and identify the positive and negative risks involved in that task. Positive risks are the things that could make it take less time and negative risks are the things that could make it take longer.
2. Then you ask the team member to make three estimates. The first estimate is a best guess (BG). It is the average amount of work the task might take if the team member performed it 100 times. The second estimate is the pessimistic (P) estimate. That is how much work the task would take if the identified negative factors occur. Last, you ask for an optimistic (O) estimate. That is how much work the task would take if the identified positive risks occur.
3. Next you do some simple mathematics with the three estimates. You calculate the mean and standard deviation applying the 3-point (PERT) estimating formulas to the estimates the team member gave you. (O + 4BG + P) ÷ 6 equals the weighted mean. P-O/6 is the standard deviation (used for calculating probabilities). The mean estimate is the one you use for the task. It reflects the amount of risk in the task and the severity of the impact of the optimistic and pessimistic risks.
Presenting the Results of 3-point Estimates to Stakeholders
This technique is new in many organizations and you need to explain it to the project’s sponsor and stakeholders. Watch the following video to see a project manager develop and present 3-point estimates to the sponsor and some difficult stakeholders.
You can learn these techniques for PERT or 3-point estimating in our online project management courses. You’ll work privately and individually with a expert project manager. You control the schedule and pace and have as many phone calls and live video conferences as you wish. Take a look at the course in your specialty.