... microheterogeneity and its consequences for model construction and policyevaluation.17NBER WORKING PAPER SERIES ACCOUNTING FOR HETEROGENEITY, DIVERSITY AND GENERAL EQUILIBRIUM IN EVALUATING SOCIAL PROGRAMS James ... of Inequality in Tax Policy,” January 21-22, 1999 in Washington, D.C. I am grateful to Christopher Taber for help in conducting the tax simulations, and toJeffrey Smith for help in analyzing ... section. At a point in time.we caimot observe a person simultaneously in the treated and untreated state. In general. wecannot form the gain of moving from "0" to 1" and L— for anyone....