数据如下
nsw.dta
(22.14 KB)
对OLS回归
. reg reg re78 treat age education black hispanic married nodegree re75
处理效应是806
对heckit是
replace re78= . if re78==0
heckman re78 treat age education black hispanic married nodegree re75 , select (treat age education black hispanic married nodegree re75 ) twostep
处理效应是-33
为啥结果差这么多?OLS不是一般会低估处理效应吗,为啥还比heckit高?
如能帮助,多谢多谢鞠躬谢!


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