Expected Delays in Completing Projects under Uncertainty

A method is proposed to estimate, rationally, a contingency covering probable delays in completing projects. Project completion time is assumed random variable distributed normally with given expected value and variance. Two pure strategies and a mixed strategy for decreasing expected delay, if it turns out to be unacceptable, are presented. A new function SDF(ZC), as a function of a standard normal variable ZC corresponding to contract time TC, is derived and given also in a table form for calculation simplicity. The mixed strategy of compressing both expected project completion time and its variance, to achieve a desirable level of expected project delay, leads to a nonlinear program and solved by Solver/Excel.