# b)	Estimate the model using data cps_small.gdt. 
# Do the estimated coefficients have expecting signs? 

genr exper2 = exper*exper

ols wage 0 educ exper exper2

# c)	Test the hypothesis that education had no effect on wages. 
# What do you conclude? Do the same for experience.


# d)	Test whether the model suffers from heteroskedasticity problem. 
# What do you conclude?

series uhat1 = $uhat

gnuplot  uhat1 educ

gnuplot  uhat1 exper

ols wage 0 educ exper exper2
modtest --white


# e)	Suppose you are interested in expected wage difference between black and white people. 
# Modify the model, estimate it and comment to any differences for two groups. 

ols wage 0 black 
ols wage 0  black white

# f)	Now suppose you are also interested in examining returns to education 
# for black and white people.
# Make necessary changes into the model, estimate it and comment to any
# differences for two groups. 

ols wage 0 black educ

genr educ_black = educ*black
ols wage 0 educ_black