The earned income tax credit and infant health revisited
质疑Hoynes等人(2015)关于劳动所得税抵免(EITC)全国性扩张降低低出生体重率的结论，指出其双重差分估计存在识别问题、安慰剂检验失败，且缺乏合理机制，认为识别全国性政策的小因果效应极为困难。
Hoynes, Miller, and Simon (2015), henceforth HMS, report that the national expansion of the Earned Income Tax Credit (EITC) is associated with decreases in low birth weight. We question their findings. HMS's difference-in-differences estimates are unidentified in some comparisons, while failed placebo tests undermine others. Their effects lack a plausible mechanism as the association between the EITC and prenatal smoking also fails placebo tests. We contend that the waning of the crack epidemic is a possible confound, but we show that any number of policies directed at poor women also eliminate the effect of the EITC when aggregated to the national level. Identifying small, causal effects of a national policy at a single point in time is exceedingly challenging.