An Introduction to Propensity Scores: What, When, and How

The use of propensity scores as a method to promote causality in studies that cannot use random assignment has increased dramatically since its original publication in 1983. While the utility of these approaches is important, the concepts underlying their use are complex. The purpose of this article is to provide a basic tutorial for conducting analyses using propensity scores and what researchers should be aware of in reading papers that choose propensity scores as a method, as well as in conducting their own research. In addition to the explanations given, examples are presented, based on actual studies, which illustrate the use of propensity scores for regression adjustment, stratification, and matching. The syntax, datasets, and output used for these examples are available on http://jea.sagepub.com/content/early/recent for readers to download and follow.