library(AER); library(stargazer)

#restringir a salarios observados non-missing
oursample <- subset(MROZ, !is.na(wage))

# primeiro estagio: forma reduzida
stage1 <- lm(educ ~exper + I(exper^2)+ motheduc+fatheduc, data=oursample)

#segundo estagio
man.2SLS <- lm(log(wage) ~fitted(stage1)+exper+ I(exper^2), data=oursample)

#2SLS automatico
aut.2SLS <- ivreg(log(wage) ~ educ+exper+I(exper^2)|motheduc+fatheduc+exper+I(exper^2), data=oursample)

# tabelas resultados
stargazer(stage1,man.2SLS,aut.2SLS, type="text", keep.stat=c("n","rsq"))

#motheduc como instrumento
aut.2SLSmoth <- ivreg(log(wage) ~ educ+exper+I(exper^2)|motheduc+exper+I(exper^2), data=oursample)

#fatheduc como instrumento
aut.2SLSfath <- ivreg(log(wage) ~ educ+exper+I(exper^2)|fatheduc+exper+I(exper^2), data=oursample)

#tabelas resultados
stargazer(aut.2SLS, aut.2SLSmoth, aut.2SLSfath, iv, type="text", keep.stat=c("n","rsq"))