A LOGNORMAL APPROXIMATION OF ACTIVITY DURATION IN PERT USINGTWO TIME ESTIMATES

摘要

The success behind effective project management lies in estimating the time for individualactivities. In many cases, these activity times are non-deterministic. In such situations, theconventional method (PERT) obtains three time estimates, which are then used to calculate theexpected time. In practice, it is often difficult to get three accurate time estimates. A recentpaper suggests using just two time estimates and an approximation of the normal distribution toobtain the expected time and variance for that activity. In this paper, we propose an alternatemethod that uses only two bits of information: the most-likely and either the optimistic or thepessimistic time. We use a lognormal approximation and experimental results show that ourmethod is not only better than the normal approximation, but also better than the conventionalmethod when the underlying activity distributions are moderately or heavily right skewed.