* Olympic Example
  Use a quadratic regression model to
  fit the olympic.txt dataset;
options linesize=70 nodate;
data olympic;
   infile "c:/datasets/olympic.txt" firstobs=2;
   input fat chlor;
   fatsq = fat * fat;
   label fat="Fat Intake"
         fatsq="Fat * Fat"
         chlor="Blood Chloresterol";

* Try a linear regression model first;
proc reg;
   title "Olympic Example";
   model chlor=fat;
   plot r.*p. r.*npp.;

* Quadratic regression model;
proc reg;
   model chlor=fat fatsq;
   plot r.*p. r.*npp.;

* proc glm can also be used for quadratic model.
  Advantage: extra variable fatsq not needed,
  Disadvantage: no plot option available,
     residuals must be saved in separage dataset;
proc glm;
   model chlor=fat fat*fat;
   output out=out r=resid p=predict;

* Produce residual plot;
proc gplot;
   plot resid * predict;

run;
quit;