MS Project calculations and methodologies

PERT Analysis

Program Evaluation and Review Technique (PERT) is a variation on Critical Path Analysis that takes a slightly more skeptical view of time estimates made for each project stage (Mind Tools, 2011). To use this method it is necessary to acquire an estimate of the shortest possible time each activity will take, the most likely duration, and the longest time that might be taken if the activity takes longer than expected. This adds another dimension of complexity to the critical path method however it also allows to account for a range in various task durations; which represents something much closer to reality than using just one estimate.

For example, take a construction project. With good weather and no major delays the concrete foundation could be poured in two days. However, this hardly ever actually happens and project delays such as weather could drag the duration out as much as a couple weeks. If it did rain then the construction crews might have to wait a week for the ground to dry out. Therefore using this equation in a PERT analysis allows for a project manager to account for some of the variation in task activities.

The PERT approach was originally developed by the U.S. Navy to manage some of their more complex projects that have numerous dependent activities (Net MBA, 2011). It allowed them to consider the range in various task duration rather than simply just use one number. Another advantage to this approach is that it is developed using the normal distribution model. Therefore it is possible to determine probabilities of the project being completed on time as well as individual activities. For example, if you have the shortest duration for a task, the expected duration, and the longest possible estimate then you can calculate the probability of the task occurring on time. Consider a task that in which the shortest duration was two days, the expected was four days, and the longest was ten days. Using the normal distribution you could make a specific estimate of the task being completed in 5 days; say eight six percent for example.