 In this case basic modeling assumptions have been challenged on empirical grounds. Elizabeth Bruch and Robert Mare use sociological data on racial preferences, challenging the sharp cut-off employed in the Schelling model (Bruch &amp; Mare 2006). They claim on the basis of simulation that the Schelling effect disappears when more realistically smooth preference functions are used instead. Their simulations and the latter claim turn out to be in error (van de Rijt, Siegel, &amp; Macy 2009), but the example of testing the robustness of simple models with an eye to real data remains a valuable one.