/*  Monthly average calls per day (100 calls)
    from Jan 1962 to Dec 1976. There was free
    local directory calls until March 1974.
    See Bowerman and O'Connell (1993, p.678).
*/
options ps=58 ls=80 pageno=1;
data teleph;
  infile 'tel.dat';
  title 'Telephone calls FROM 1962-1976';
 input y@@;
 time=_n_;
 newpol=(time ge 147);  /* Intervention: March 1974 */
 proc arima data=teleph;
  i var = y(1,12);
  e q=(12);
/*
   Fit a model using abrupt change
*/
  i var = y(1,12) crosscorr=(newpol(1,12));
  e q=(12) input=newpol noconstant
    printall altparm maxit=30 backlim=-3 plot;
  f lead=12;
/*
   Fit another model using gradual change
*/
  i var = y(1,12) crosscorr=(newpol(1,12));
  e q=(12) input=(0$/(1) newpol) noconstant
    printall altparm maxit=30 backlim=-3 plot;
  f lead=12;
 run;