In this article, we apply a generalization of the propensity score of Rosenbaum and Rubin (1983b). Techniques based on the propensity score have long been used for causal inference in observational studies for reducing bias caused by non-random treatment assignment. In last years, Joffe and...

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)....