期刊名称：Discussion Papers of the Department of Economics, University of St.Gallen = Diskussionspapiere der Volkswirtschaftlichen Abteilung der Universität St.Gallen
出版年度：2005
卷号：2005
出版社：Universität St. Gallen
摘要：The paper addresses the issue of potentially endogenous control variables in evaluation studies based on the assumption that selection bias can be avoided by conditioning on observed variables. It shows that the standard formulation of the conditional independence (CIA) or selection on observables assumption obscures the endogeneity problem. The paper clarifies the issue by suggesting a CIA based on exogenous (potential) outcomes as well as explicit exogeneity conditions. The refined CIA allows to asses the endogeneity bias as well as the plausibility of the CIA, because it allows a separate discussion of (i) the problems of missing variables that are necessary to avoid selection bias, and (ii) the problem that some of the control variables may be influenced by the treatment.
