  There is a large literature on semiparametric estimation of average treatment
effects under unconfounded treatment assignment in settings with a fixed number
of covariates. More recently attention has focused on settings with a large
number of covariates. In this paper we extend lessons from the earlier
literature to this new setting. We propose that in addition to reporting point
estimates and standard errors, researchers report results from a number of
supplementary analyses to assist in assessing the credibility of their
estimates.
