Comparison of alternative approaches to trim subjects in the tails of the propensity score distribution

PURPOSE: In nonexperimental comparative effectiveness research, restricting analysis to subjects with better overlap of covariate distributions, hence greater treatment equipoise, helps balance the groups compared and can improve validity. Three alternative approaches, derived from different perspectives, implement restriction by trimming observations in the tails of the propensity score (PS). Across approaches, we compared the relationships between the overlap in treatment-specific PS distributions and the size of the balanced study population after trimming. METHODS: The three trimming approaches considered were absolute trimming to the range 0.1