Q: What is a propensity score matching (PSM)?
Answer: Propensity score matching is a balancing score to minimize the effect of confoundings by accounting for most of the measurable covariates between the treated and untreated subjects. Propensity score can allow to design and analyze an observational study so as to mimic the characteristics of a randomized study. From a linear combination of a large observation data (a large number of covariates), a single score is obtained balancing the treatment and control groups without losing a large number of observations. It is a powerful tool and most of the commercially available biostatistics software have an implementation to measure it.
Austin P.C. A critical appraisal of propensity score matching in the medical literature from 1996 to 2003. Statistics in Medicine. 2008b;27:2037–2049.