A Note on the Robustness of Card and Krueger (1994) and Neumark and Wascher (2000)

This note adds to the discussion originating from David Card and Alan B. Krueger (1994; CK) and David Neumark and William Wascher (2000; NW). It re-evaluates their results by using the semiparametric difference-in-differences estimator introduced by Alberto Abadie (2005). The re-evaluation suggests that the original results on the average employment effect in CK and NW are fairly robust, although the NW results are slightly diluted when taking into account the differences in the distributions of the observed covariates