双向固定效应模型,两个工具变量,2sls命令这样写对吗?xtivreg2 y (x1=a b), fe i(Year)
其中b是x1的滞后项, 用
xtset Company Year
gen b =l.x1
生成滞后项后,再用xtivreg2 y (x1=a b), fe i(Year)显示time and panel variables previously xtset -- may not be changed by options t() and i() -- use xtset to change them
请问这是怎么回事?应该怎么办?