Bias in Pert Project Completion Time Calculations for a Real Network

Among network techniques recently widely employed in program management, Pert is addressed to the problem of assessing the manager's chances of completing a project on time. Theory and monte carlo simulation have shown that the Pert method yields results which are biased high, and this paper discusses a real example involving conditions under which the bias is very large. The manager is thus grossly misled into thinking his chances are very good, when in reality they are very poor. If the manager's network has multiple parallel paths with relatively equal means and large variances, Pert calculations will be considerably biased. Simulation can be utilized to estimate the distribution of completion time in this case, and guide the manager in appraising and controlling his chances of completion.