2.4 Program Evaluation and Review Technique (PERT)
• In CPM we assume that each activity has a fixed time, in practice the task lengths vary. This variation can be shown with the Beta distribution.
• task times are expressed with three numbers separated by dashes to-tm-tp to represent task times.
• the mean (effective) time can be found with,
• A Standard Deviation for each activity time can be approximated using,
• The te valuaes can be used to do a CPM analysis of a network diagram. Once the Critical Path is identified the overal task time and variance can be calculated using,
• To find the chance that the process will be done by the time Ts, the z value can be calculated. The z value can then be used to find the probability of completion using the cummulative normal distribution function.