Estimating the Mean and Variance of Activity Duration in PERT

The traditional PERT (Program Evaluation and Review Technique) model uses beta distribution as the distribution of activity duration and estimates the mean and the variance of activity duration using “pessimistic”, “most likely ” and “optimistic ” time estimates proposed by an expert. In the past several authors have modified the original PERT estimators to improve the accuracy. In this paper, on the basis of the study of the PERT assumptions, we present an improvement of these estimates. At the end of the paper, an example is presented to compare with those obtained using the proposed method as well as other method. The comparisons reveal that the method proposed in this paper is more effective in determining the activity criticalities and finding the critical path