若运行如下指令总是报错:
. xi:xtreg cc1 ip lev cfo growth age mb top1 seo soe big4 roe if size<=22.04724 i.year i.ind,fe cluster(id)
i.year _Iyear_2013-2018 (naturally coded; _Iyear_2013 omitted)
i.ind _Iind_1-75 (_Iind_1 for ind==专业技术服务业 omitted)
invalid '_Iyear_'
r(198);
end of do-file
r(198);
但运行如下指令则没问题:
xi:xtreg cc1 ip lev cfo growth age mb top1 seo soe big4 roe if size i.year i.ind,fe cluster(id)
请问各位大神,这种情况是什么原因,要怎么解决???谢谢!!!