What is PERT and how does it differ from a purely deterministic CPM estimate?

What is PERT and how does it differ from a purely deterministic CPM estimate?

• A. PERT uses optimistic, most likely, and pessimistic estimates to compute a weighted expected duration; it provides a probability-based schedule, while CPM uses fixed estimates.
• B. PERT ignores uncertainty.
• C. PERT and CPM are identical.
• D. PERT uses only most likely estimates.

Answer: (A)

PERT incorporates uncertainty in activity durations by using three-point estimates—optimistic, most likely, and pessimistic—for each activity. These estimates are combined into a weighted expected duration for the activity, commonly TE = (O + 4M + P)/6, which gives a mean duration and a measure of variability (variance = ((P - O)/6)^2). Because each activity now has a distribution rather than a single fixed time, the overall project duration becomes probabilistic, allowing you to estimate the probability of finishing by a certain date. CPM, on the other hand, uses a single fixed duration for each activity, yielding a deterministic schedule with a definite critical path and no explicit probability distribution for completion times. So the described distinction—using optimistic, most likely, and pessimistic estimates to compute a weighted expected duration and producing a probability-based schedule, versus relying on fixed estimates—is why that option is correct.

PERT incorporates uncertainty in activity durations by using three-point estimates—optimistic, most likely, and pessimistic—for each activity. These estimates are combined into a weighted expected duration for the activity, commonly TE = (O + 4M + P)/6, which gives a mean duration and a measure of variability (variance = ((P - O)/6)^2). Because each activity now has a distribution rather than a single fixed time, the overall project duration becomes probabilistic, allowing you to estimate the probability of finishing by a certain date.

CPM, on the other hand, uses a single fixed duration for each activity, yielding a deterministic schedule with a definite critical path and no explicit probability distribution for completion times.

So the described distinction—using optimistic, most likely, and pessimistic estimates to compute a weighted expected duration and producing a probability-based schedule, versus relying on fixed estimates—is why that option is correct.