= Matching = '''Matching''' is a pre-processing technique. <> ---- == Description == Matching is generically a method for identifying similar observations, based on covariates. Exact matching means taking a treated case and identifying an untreated case that has equivalent values for all covariates. Analysis is then performed on just the matched sample; all unmatched cases are deleted. A necessary follow-up step is ensuring that the matched sample is balanced. '''Coarsened Exact Matching''' ('''CEM''') is a modification of that approach; covariates are 'coarsened' by [[Statistics/Binning|binning]], so as to encourage more 'exact' matches. Analysis should be performed with the matched sample and the original, un-coarsened variables. '''Propensity score matching''' ('''PSM''') models the propensity of being 'assigned' the treatment, giving a 'propensity score'. Cases are then matched based on similarity of the scores. ---- == Usage == === Weighting === When redistributing weights from non-respondents to respondents, a uniform adjustment is often used. A more nuanced method is to design weighting classes using propensity scores (wherein 'treatment' is response), and then calculating a uniform adjustment per class. This ensures weight transfers between similar cases. ---- CategoryRicottone