Dear Statalisters,

I am trying to run two schooling regressions: one for boys and one for girls. In none iv-regressions, I know how to run it correctly. But in the instrumental variable case, I am lost.

My code:
gen group = cond(SEX== 0, 0, 1) xtivreg MATH c.AGE#i.group c.HEALTHRESTRICTIONS#i.group c.PARENTALCARE#i.group c.PARENTALEDUCATION#i.group c.PARENTALINCOME#i.group c.YEAR#i.group (ACTIVE = c.summary#i.group), re test 1.group#c.ACTIVE = 0.group#c.ACTIVE The error is:

regressor I1.group#C.ACTIVE not found

Does anyone know how to compare the second stage results?

Thank you very much for your appreciate help.