/* wheatprot.sas */
options ls=72 ps=60;
data wheat;
   infile 'wheatprot.dat';
   input yield protein;
   yield2 = yield*yield;
proc print data=wheat;
title 'wheat protein data';
proc plot data=wheat;
   plot protein*yield;
title 'wheat protein data scatterplot';
proc glm data=wheat;
   model protein = yield / ss1 ss2 p;
      output out=new1 predicted=yhat residual=resid;
title 'simple linear regression of protein on yield';
proc plot data=new1;
   plot resid*yield / vref=0;
title 'residual plot: regression of protein on yield';
proc glm data=wheat;
   model protein = yield yield2 / ss1 ss2 p;
      output out=new2 predicted=yhat2 residual=resid2 lcl=clpl
             ucl=clpu lclm=clml uclm=clmu;
title 'quadratic regression of protein on yield';
proc print data=new2;
   var protein yield clml clmu clpl clpu yhat2 resid2;
proc plot data=new2;
   plot resid2*yield / vref=0;
title 'residual plot: quadratic model';
proc univariate data=new2 plot;
   var resid2;
title 'descriptive statistics for residuals';
proc rank data=new2 normal=blom out=new2a;
   var resid2;
   ranks nscore;
proc plot data=new2a;
   plot nscore*resid2;
title 'normal probability plot for residuals';
run;