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Probability of Project CompletionIntroductionWhen developing a project schedule, the project manager aspires for the project to be completed on time. However, the project manager should anticipate a delay. Another possibility is an early completion of the project. The project manager might consider the probability or likelihood of each outcome.Learning MaterialsThe critical path analysis determines the expected project completion time. However, there may be significant variation in the time estimates for activities. Variations of activities on the critical path can impact the overall completion time.Early Completion and DelayIf activities are completed early, the completion date will be prior to the expected date. Or, there could be a possible delay. An early completion should not concern the project manager, but a delay could be worrisome. Variance of the Complete ProjectThe variance of the complete project is computed by summing the variances of the activities on the critical path. The project standard deviation is the square root of the project variance.Project variance = σ²p= ∑ (variances of activities on critical path)ExampleGiven the project example used in this section with the critical path of Start-A-C-E:The project variance = variance of activity A + variance of activity C + activity of activity E=0.11 + 1.78 + 0.11=2.0The project standard deviation = √project variance = √2.0 = 1.41 weeks.Using PERTUsing the project variance and standard deviation, program evaluation and review technique (PERT) uses the following two assumptions:
Total project completion times follow a normal probability distribution.