The use of spectral analysis to validate peanning models

Statistical fit of model predictions to empirical evidence is found to be an insufficient condition for establishing the validity of a planning model where the dynamic behavior is of particular importance. The paper describes a spectral analysis statistical test that can be used to validate the structure of a planning model by comparing the time series generated by the model with the actual time series of events for the real system under study. Validation of an ambulance simulation model is reported in which the model apparently was valid based on classical goodness of fit tests of aggregate data. However, following a spectral analysis of the simulation results, an entirely new method of generating incidents was found to be necessary. The resulting model then was able to duplicate realistically the essential cyclical nature of hourly demand for emergency care observed in the real system which periodically created excessive busy and idle periods not realized in the structure of the original model.