* PS9.1, using DATA6-6, for Example 9.1 illustrating autocorrelation 
read(data6-6) year farmpop
genr time=year-1947
ols farmpop time / resid=ut predict=yhat exactdw
genr ut1=ut(-1)
plot ut time
sample 2 44
stat ut ut1 / pcor
* sample 2 44 is needed because ut1 is undefined for t=1
stop