# PS5.1, to verify Example 5.1 and Table 5.1 
open data4-3
ols housing 0 intrate pop gnp 
# compute absolute percentage error 
genr ape3 = 100*abs($uhat)/housing
# compute mean percentage error 
genr mape3 = mean(ape3)
# Model B 
omit pop
genr ape2 = 100*abs($uhat)/housing
genr mape2 = mean(ape2)
# Model A 
ols housing 0 intrate pop
genr ape1 = 100*abs($uhat)/housing
genr mape1 = mean(ape1)
# Correlation coefficients 
corr gnp pop intrate 
print mape1 mape2 mape3
# carry out joint F-test for coefficients of pop and gnp 
ols housing 0 intrate pop gnp 
omit pop gnp 

