#  PS6.6 for Application Section 6.7
open data3-3 
ols PATENTS 0 R_D 
# generate lagged variables 
genr R_D1 = R_D(-1)
genr R_D2 = R_D(-2)
genr R_D3 = R_D(-3)
genr R_D4 = R_D(-4)
# print them to see that missing observations are denoted by -999 
print R_D R_D1 R_D2 R_D3 R_D4
# generate square terms 
square R_D R_D1 R_D2 R_D3 R_D4  
# reset sample range because lagged variables are undefined for the 
# period 1960-63 
smpl 1964 1993
# estimate the most general urestricted model 
ols PATENTS const R_D R_D1 R_D2 R_D3 R_D4 sq_R_D \
 sq_R_D1 sq_R_D2 sq_R_D3 sq_R_D4 
# omit variables with p-values above 0.9  
omit 3 5 11 
# omit variables with p-values above 0.5 
omit 7 9 10 
# omit one at a time 
omit 8 
omit 4 
# compute predicted values 
genr pred = PATENTS - $uhat
# save residuals 
genr error = $uhat
# compute absolute % error 
genr abspcerr = 100*abs(error)/PATENTS
# print values as in a table with the -o flag 
print -o R_D PATENTS pred error abspcerr 

