# PS9.4, for Example 9.5 
open data6-6
genr time 
# graph farmpop against year 
graph farmpop year 
# linear time trend 
ols farmpop 0 time 
# generate square of time 
genr timesq = time*time
# quadratic time trend 
ols farmpop 0 time timesq 
# compute growth rate of farmpop 
genr gfarmpop=ldiff(farmpop)
# suppress 1948 observation 
smpl 1949 1991
# time trend for log difference 
ols gfarmpop 0 time 
