黄老师,按照您给的方法,解决过后ivreg2 Y (ind = distance) dyear1-dyear2 dpref_code1-dpref_code67, robust 可以显示结果,但是我加入其他控制变量后,ivreg2 Y (ind = distance) age edu hhsize PC phouse SC ln_wage_h ln_ev_gdp ln_fdi dyear1-dyear2 dpref_code1-dpref_code67, robust ,就会报错:equation not identified; must have at least as many instruments not in
the regression as there are instrumented variables
请问该如何解决呀