/* iowacorn2.sas */
options ls=72 ps=60;
data iowacorn;
   infile 'iowacorn.dat';
   input x1 x2 x3 x4 x5 x6 x7 x8 x9 y;
/* coding
   x1 = year
   x2 = precip1
   x3 = maytemp
   x4 = junerain
   x5 = junetemp
   x6 = julyrain
   x7 = julytemp
   x8 = augrain
   x9 = augtemp
   y = yield     */
/* regression of yield on x1, x2, x3 */
proc glm data=iowacorn;
   model y = x1 x2 x3 / ss1 ss2 clparm;
      output out=new1 predicted=yhat residual=resid
          lcl=clpl ucl=clpu lclm=clml uclm=clmu;
title 'regression of yield on x1, x2, x3';
proc print data=new1;
   var y x1 x2 x3 clml clmu clpl clpu yhat resid;
proc plot data=new1;
   plot resid*yhat / vref=0;
   plot resid*x1 / vref=0;
   plot resid*x2 / vref=0;
   plot resid*x3 / vref=0;
title 'residual plots: regression of y on x1, x2, and x3';
proc rank data=new1 normal=blom out=new1a;
   var resid;
   ranks nscore;
proc plot data=new1a;
   plot nscore*resid;
proc univariate data=new1 plot normal;
   var resid;
/* use proc reg to get sequential regression coefficients */
proc reg data=iowacorn;
   model y = x1 x2 x3 / seqb ss1 ss2;
title 'regressions with sequential coefficients';
run;