A systematic approach to stochastic scheduling

A systematic methodology extends CPM project planning to allow for uncertainties, decision points, alternative courses of action, and likely changes and failures while executing the plan. Stochastic scheduling is carried out in eight steps. (1) The basic process and network are defined. (2) Uncertainty conditions are specified. (3) These conditions are formulated as a set of probability states, with corresponding durations and costs. (4) An augmented stochastic network is constructed. (5) From average values, durations and costs, a deterministic network is solved to provide an approximate picture of expected outcomes. (6) The stochastic network is solved, using a simulator; and the uncertainty effects of the stochastic conditions are analysed. (7) The effects of individual conditions on overall uncertainty are analysed. (8) An attempt is made to eliminate or modify those conditions contributing the most to uncertainty. The number of iterations needed to obtain a satisfactory simulation is also discussed. The stability of time and cost distributions is found to increase as the square root of the number of iterations.