* PS9.4, using DATA6-6, for Example 9.5
read (data6-6) year farmpop
genr time = year - 1947
* graph farmpop against year
plot farmpop year 
* linear time trend
ols farmpop time 
* generate square of time
genr timesq = time*time
* quadtratic time trend
ols farmpop time timesq 
* compute growth rate of farmpop
genr gfarmpop=log(farmpop)-log(farmpop(-1))
* suppress 1948 observation
sample 2 44
* time trend for log difference
ols gfarmpop time 
stop