# Verbeek returns to schooling
require("gmm")
require("foreign")

data<-read.dta("/home/cbrunos/Copy/schooling.dta")

attach(data)


# Regression page 139
reg <- lm(lwage76~ed76 + exp76 + exp762 + black + smsa76 + south76)
summary(reg)
# Same results as in book

dat <- as.matrix(cbind(ed76,exp76,exp762,black,smsa76,south76))


mom<-function(theta,dat)
{
  m <- array(0,dim=c(3010,7))
  m[,1] <- lwage76-seq(1,length(lwage76)*theta[1])
  for (i in 1:6){
  m[,i+1] <- t(dat[,i])%*%(lwage76-dat[,i]*theta[i+1])
  #f <- cbind(m)
  }
  return(m)
}

res <- gmm(mom,x=dat,t0=c(0,0,0,0,0,0,0))

summary(res)

# GMM above is not working; try with another data set?