The covalidation of dissimilarly structured strategic airlift models

A methodology is presented which allows comparison between models constructed under different modeling paradigms. Consider two models that exist to study different aspects of the same system, specifically Air Mobility Command's strategic airlift system. One model simulates a fleet of aircraft moving a given combination of cargo and passengers from an onload point to an offload point. The second model is a linear program that optimizes aircraft and route selection given cargo and passenger requirements in order to minimize late and nondeliveries. Further, the optimization model represents a more aggregated view of the airlift system than does the simulation. The two models do not have immediately comparable input or output structures, which complicates comparisons between the two models. We develop a methodology that structures this comparison and use it to compare the two large-scale models described above. Further, our technique has the fortunate byproduct of improving the fidelity of the models through a series of iterative refinements of the input to each model based on the output of the other. Models that compare favorably with regard to our methodology are deemed covalid models.