library(AER); library(lmtest)

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

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

#segundo estagio
stage2 <- lm(log(wage)~educ+exper+I(exper^2)+resid(stage1), data=oursample)

#resultados incluindo testes t
coeftest(stage2)