Summary PERT/CPM

PERT
Saturday, January 23, 2021 6:16 PM



PROBABILISTIC TIME ESTIMATES
- Beta distribution used to describe variability in activity durations
- The main determinant of the way CPM/PERT networks are used is
whether activity/work package durations are probabilistic or
deterministic

Three point estimate methods
- The probabalistic PERT/CPM approach that incolved 3 duration
estimates for each activity/work package instead of one:
• Optimistic time = t0
○ The length of time required under optimal
conditions
• Most likely time = tm
○ The most probable length of time required
○ Time required in most common or normal
conditions
• And pessimistic time = tp
○ The length of time required under the worst
conditions
○ Under most commonly disadvantageous
situations




BETA DISTRIBUTION
- Continuous positive distributions used to describe variability
- Path duration distribution is approximately a normal distribution



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,
, BETA DISTRIBUTION
- Continuous positive distributions used to describe variability
- Path duration distribution is approximately a normal distribution



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EXPECTED TIME Te
- Once you have the probabilistic time estimates can compute the mean
time:
- Te = weighted averge of the 3 time estimates


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- Expected duration of a path = sum of the expected times of the
activities on that path


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