I’m oftenasked how the matching weights produced by MatchIt are computed. The weights are necessary for estimating the treatment effect in the matched sample; indeed, the weights determine the matched sample. While the weights for simple methods like 1:1 matching are straightforward (i.e., 1 if matched and 0 if unmatched), for more complicated scenarios, like full matching, matching with replacement, and variable ratio matching, the weights take on variable values and are critical to includ...
