请教一下各位老师、大神们下面可能是哪里出问题了?
情况是这样的:选择了2008年和2009年两年的数据,政策改革是在09年开始实行的,分为对照组和实验组。想用PSM+DID来评价政策效果。
因变量是OFDI存量,自变量是treated(参与改革treated=1,不参与改革treated=0),t(改革前t=0,改革后t=1),协变量:PGDP,Ps, At, Eu, Cp
输入psm-did命令:
diff OFDI,t(treated) p(t) kernel id(id) logit cov(PGDP Ps At Eu Cp) report support
之后报错显示:KERNEL PROPENSITY SCORE MATCHING DIFFERENCE-IN-DIFFERENCES
Estimation on common support
Report - Propensity score estimation with logit command
Atention: _pscore is estimated at baseline
outcome does not vary; remember:
0 = negative outcome,
all other nonmissing values = positive outcome r(2000);