ABSTRACT
Variability between actual duration and planned duration of any project activity is a basic and common form of uncertainty in the project conditions. The Project Evaluation and Review Technique (PERT) concept was devised in the late 1950s and dealt with project durations; it recognized that uncertainty is a feature of all estimating and it sought to quantify this by allowing estimates of the shortest, longest and most likely task durations to be entered into the analysis. PERT and PERT/Cost contained a method of calculation of the range of possible outcomes for the costs and durations associated with a project plan; however, by using the variance they took a mathematical short-cut to the answer and this was necessary with the relatively low-powered computers of the early 1960s. Two methods have been devised for calculating the end result: direct calculation using the rules of probability and random number simulation.
