Effects of the application of activity calendars on the distribution of project duration in PERT networks

The Program Evaluation and Review Technique (PERT) has been criticized for the proposed (beta) distribution of the activities, the three-point estimation method, the assumption of task independence and the assumed distribution of the project duration since its birth. Developments and generalizations of the succeeding years and decades were mostly aimed at resolving these issues. However, there are still pending questions that have not been examined in detail, if at all. One of these issues is the effect of activity calendars on the distribution of the project duration. Using a simple artificially created project we prove that the application of activity calendars has a greater influence on the distribution of the project duration than any of the above-mentioned criticisms. In the absence of analytic solutions, a robust tool performing Monte Carlo simulations has been used for calculations.