I'm not sure about the statistical proc, but if you just want to add an 'x' variable to your dataset, that contains the observation id, maybe something like this will work ...   data session3.combinedfiles; set session3.combinedfiles; x=_n_; y=log(PCECC96); x1=log(DPIC96); x2=log(MPRIME); run; ... View more

If you want the variable to be named x, then use x = _n_; ... View more