For projects with highly uncertain activity durations, what three specific estimates does PERT require for each activity?

For projects with highly uncertain activity durations, PERT, or Program Evaluation and Review Technique, requires three specific time estimates for each activity to account for variability and provide a more realistic expected duration. These estimates are: the optimistic duration, the pessimistic duration, and the most likely duration. The optimistic duration represents the shortest possible time an activity could be completed, assuming everything goes perfectly without any setbacks or issues. It signifies the best-case scenario. The pessimistic duration represents the longest possible time an activity might take, assuming everything that could reasonably go wrong does go wrong, but excluding catastrophic events. This accounts for foreseeable difficulties and delays. The most likely duration is the most realistic assessment of the time an activity will take under normal circumstances, reflecting the duration an experienced team member would expect, considering typical conditions and expected minor issues. These three estimates collectively help to define a range of possible durations for an activity, enabling PERT to calculate a weighted average expected duration and assess the probability of project completion by a certain date.