# PS5.2, for Example 5.2 and Table 5.2
open data3-7 
ols cost 0 age
# compute absolute percentage error 
genr ape1 = 100*abs($uhat)/cost
# compute mean percentage error 
genr mape1 = mean(ape1)
# Model B 
ols cost 0 miles
genr ape2 = 100*abs($uhat)/cost
genr mape2 = mean(ape2)
# Model C 
ols cost 0 age miles
genr ape3 = 100*abs($uhat)/cost
genr mape3 = mean(ape3)
# Correlation coefficients 
corr age miles
print mape1 mape2 mape3 
