Propensity Score Matching Methods for Non-Experimental Causal Studies.

This paper considers causal inference and sample selection bias in non-experimental settings in which: (i) few units in the non-experimental comparison group are comparable to the treatment units; (ii) selecting a subset of comparison units similar to the treatment units is difficult because units must be compared across a high-dimentional set of pretreatment characteristics. We propose the use of propensity score matching methods, and implement them using data from the NSW experiment.