A Bounding Technique for Probabilistic PERT

Bounding time distributions has been an effective way of improvements of the original PERT method. Analytical enhancement of PERT is often an effective time bounding approach. However, one thing that is missing today is a combination of time distributions which parameters can be effectively obtained empirically and the effective bounding technique for them. We aim at addressing this gap and suggest Cornish-Fisher expansion (CFE) to compute time bounds in formal models like the classical PERT. We argue that CFE allows us to evaluate analytically approximate time bounds easily without resort to simulations. This bounding approach is useful in case of complex distribution functions of task durations, because analytical derivation of project completion time distribution is tedious. Our example shows CFE usage for uniform time distributions and comparison with time bounds of classical PERT.