install.packages("leaps") 
install.packages("ivreg")
library("leaps")
library("ivreg")

data = read.csv("http://hedibert.org/wp-content/uploads/2024/11/card.csv",header=TRUE) 

attach(data) 

n = nrow(data) 

# OLS regression with several exogenous variables
reg.ols = lm(lwage~educ+exper+expersq+black+smsa+south+smsa66+ reg662+reg663+reg664+reg665+reg666+reg667+reg668+reg669) 

# IV regression with several exogenous variables
reg.iv = ivreg(lwage ~ educ+exper+expersq+black+smsa+south+smsa66+ reg662+reg663+reg664+reg665+reg666+reg667+reg668+reg669 | nearc4+exper+expersq+black+smsa+south+smsa66+ reg662+reg663+reg664+reg665+reg666+reg667+reg668+reg669)


summary(reg.ols)

summary(reg.iv)





# OLS regression with selection of exogenous variables
X1 = cbind(educ,W)
data = data.frame(y=lwage,X=X1)
p    = ncol(X1)
regs = regsubsets(y~.,data=data,method="exhaustive",nvmax=p)
bic = summary(regs)$bic
ii  = 1:p
coef(regs,ii[bic==min(bic)])

ols = lm(lwage ~ educ+exper+expersq+black+smsa+south+reg663+reg668)

# IV regression with selection of exogenous variables
X1   = cbind(iv,W)
data = data.frame(y=lwage,X=X1)
p    = ncol(X1)
regs = regsubsets(y~.,data=data,method="exhaustive",nvmax=p,force.in=X1[,1])
bic = summary(regs)$bic
ii  = 1:p
coef(regs,ii[bic==min(bic)])

reg.iv = ivreg(lwage ~ educ+exper+expersq+black+smsa+south+reg663 | nearc4+exper+expersq+black+smsa+south+reg663)

summary(ols)

summary(reg.iv)