(* PS9.4, using DATA6-6, for Example 9.5 *)
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 
