50123 发表于 2016-10-11 00:00 
xi:xtreg y x1 x2 x3 x4 i.industry i.year, fe
这样就可以实现同时控制行业、年份和公司的固定效应。但是 ...
但是按这样回归后,结果是控制industry 出现多重共线被omitte了,是怎么回事呢?
note: _Iindustry_14 omitted because of collinearity
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