Comparison of experiments with simulations is at the heart of progress in physics. Experiments are required to validate models, and simulations based on those models can be used to explore new physical regimes and de ne interesting experiments. Signi cant progress, however, is intimately tied to the way in which the comparison between experiment and simulation is carried out. The procedure has been largely a matter of personal preference, and familiarity with a certain analytical technique has often been the criterion for the selection of that technique. The complexity of the problem suggests that this eclectic approach is here to stay, but the complexity also demands a better understanding of what constitutes a meaningful comparison.

LA-UR-04-8498 In the 2004 LANL LDRD report to the US Congress