The Propensity Score method in public policy evaluation: a survey.

Recently, in the field of causal inference, nonparametric techniques, that use matching procedures based for example on the propensity score (Rosenbaum, Rubin, 1983), have received growing attention. In this paper we focus on propensity score methods, introduced by Rosenbaum and Rubin (1983). The key result underlying this methodology is that, given the ignorability assumption, treatment assignment and the potential outcomes are independent given the propensity score. Much of the work on propensity score analysis has focused on the case where the treatment is binary, but in many cases of interest the treatment takes on more than two values. In this article we examine an extension to the propensity score method, in a setting with a continuous treatment.