#IV - ex1
open bwght.gdt

ols log(bwght) const packs --robust

ols log(bwght) const packs male parity log(faminc) --robust

#compare coefficients
ols log(bwght) const packs --robust
bpacks = $coeff(packs)

ols log(bwght) const packs male parity log(faminc) --robust
restrict
    b[packs] = bpacks
end restrict

# IV
tsls log(bwght) const packs male parity log(faminc); \
const cigprice male parity log(faminc) --robust

# relevance (don't look at the tsls output yet)
ols packs const cigprice male parity log(faminc) --robust

# Hausman by hand
# Reduced form for packs: 
ols packs const cigprice male parity log(faminc) --robust
resid = $uhat

# Second step Hausman test
ols log(bwght) const packs male parity log(faminc) resid --robust
omit resid --quiet
# or just look at the t-statistic for resid
# Null: packs is exogenous


# In the simple model
# IV
tsls log(bwght) const packs ; const cigprice --robust