我的回归命令是这样的:ivreg2 Y $cv i.year i.ind (X= IV_X ),r first
然后虽然两个阶段的回归结果都有显示,但是最后有个warning,这是什么情况啊,出现这种情况前面的回归结果还能用吗?或者具体要怎么做才能不出现这个warninga啊?拜托大神解答一下,感谢感谢
Warning: estimated covariance matrix of moment conditions not of full rank.
overidentification statistic not reported, and standard errors and
model tests should be interpreted with caution.
Possible causes:
singleton dummy variable (dummy with one 1 and N-1 0s or vice versa)
partial option may address problem.