大神请教个问题,作双重差分倾向得分匹配,参考的陈强老师的书,用的diff命令,结果显示
KERNEL PROPENSITY SCORE MATCHING DIFFERENCE-IN-DIFFERENCES
Estimation on common support
Report - Propensity score estimation with probit command
Atention: _pscore is estimated at baseline
outcome does not vary; remember:
0 = negative outcome,
all other nonmissing values = positive outcome
r(2000);
是什么原因呀?


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