Comments on 'A weighting analogue to pair matching in propensity score analysis' by L. Li and T. Greene.

Li and Greene (A weighting analogue to pair matching in propensity score analysis. Int J Biostat 2013;9:215-34) propose that estimates derived by the matching weight (MW) estimator are similar to those derived by the one-to-one propensity score matching estimator. The MW estimator has some useful properties, however, some regularity conditions need to be confirmed to derive an asymptotic distribution since the MW has a non-differentiable point. In this letter, we confirm the asymptotic distribution of the MW estimator and the sufficient conditions to achieve it.