The Impact of Family Income on Child Achievement: Evidence from the Earned Income Tax Credit: Comment
指出Dahl和Lochner（2012）研究中存在变量编码错误，修正后工具变量估计值降低32%，但定性结论不变。
In a recent article in the American Economic Review, Dahl and Lochner (2012) use changes in the Earned Income Tax Credit to estimate the causal effect of family income on child achievement. Their instrumental variable (IV ) estimates imply that a $1,000 increase in income raises combined math and reading test scores by about 6 percent of a standard deviation. I document a variable coding error. Correcting this error reduces the IV estimates by 32 percent; correcting this error does not change the qualitative conclusions of the study.