"The process of estimating the number of work periods needed to complete individual activities with estimated resources."
The definition shown above in italics is taken from the Glossary of the Project Management Institute, A Guide to the Project Management Body of Knowledge, (PMBOK® Guide) – Fifth Edition, Project Management Institute Inc., 2013
Project Management Institute, A Guide to the Project Management Body of Knowledge, (PMBOK® Guide) – Fifth Edition, Project Management Institute Inc., 2013 Figure 6-14 Page 166
Analogous: uses data from similar/past projects
3-point estimate or PERT
PERT technique (Project Evaluation & Review Technique)
Uses three estimates, to define an approximate range for an activity‟s duration
Σ = Expected Time or Expected Duration
O = Optimistic P = Pessimistic M = Most Likely
The standard deviation of an activity
± 1 standard deviation = 68.26%
± 2 standard deviations = 95.46%
± 3 standard deviations = 99.73%
± 6 standard deviations = 99.999998% - also known as Six Sigma
Normal distribution curve
Variance of the activity = square of the standard deviation = Sigma squared
Variance and the standard deviation measure variability, and are measures of how spread out a distribution is (from the mean)
Another term – heuristics (simple rule of thumb) – six sigma is an example
Your project has a critical path equal to 30 days and a standard deviation of 2½ days.
What will be the earliest finish and latest finish estimates for this project within a 95% confidence level?
The question gives you:
You add the resulting 5 to the project duration to give you the upper end of the variance range = 35
You subtract that 5 from the project duration to give you the lower end of the variance range = 25
The PERT Duration of the Critical Path Activities, Standard Deviation (σ), Variance (σ²), Project‟s PERT Duration, and Standard Deviation (σ Project =√ Σ variances))
If all the activities above are on the Critical Path, what is the project’s mean duration and σ ?
Project’s mean duration = 170.99 days and σ=10.1 days
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