*
* Dougherty, Introduction to Econometrics, 4th ed
* Example from Section 13.3
* Graphical analysis of non-stationary series
*
open data demand.xls
calendar(a) 1959:1
data(format=xls,org=columns) 1959:01 2003:01 adm book busi clot date dent doc dpi flow food furn gas gaso $
 hous legl mags mass opht padm pbook pbusi pclot pdent pdoc pflow pfood pfurn pgas pgaso phous plegl $
 pmags pmass pop popht prelg ptele ptob ptoys ptpe relg tele time tob toys tpe
*
set logdpi = log(dpi)
*
graph(footer="Figure 13.20 Logarithm of DPI 1959-2003")
# logdpi
@acf(method=yule,number=20,$
  footer="Figure 13.21 Sample correlogram of log DPI") logdpi
*
set dlogdpi = logdpi-logdpi{1}
graph(footer="Figure 13.22 Differenced Logarithm of DPI 1959-2003")
# dlogdpi
@acf(method=yule,number=20,$
  footer="Figure 13.23 Sample correlogram of differenced log of DPI") dlogdpi