“…Propensity scores are used to reduce the estimation bias of the treatment effect between subjects that received treatment and those subjects that did not (Austin, Grootendorst, & Anderson, 2007;D'Agostino, 1998). The propensity score, calculated for each subject, can be used in one of three ways: to match subjects on, to stratify subjects into like groups, or covarianceadjustment in a regression (D'Agostino, 1998;Qin, Titler, Shever, & Kim, 2008).…”