我用了如下命令:
heckprobit LA Q2 sex age edu pop labor land inc asset politic relation bj nj, ///
select(LD Q2 sex age edu pop labor distance land inc asset politic relation bj nj)
得到的结果显示:
selection equation:
outcome does not vary; remember:
0 = negative outcome,
all other nonmissing values = positive outcome
请问是命令有问题还是