options nocenter; goptions reset=global colors=(none);

data problem81;
 infile 'i:\.www\datasets502\EX0502.DAT' firstobs=2 dlm='09'x;
 input person sbp quet age smk;
 aq=age*quet; as=age*smk; qs=quet*smk; aqs=age*quet*smk;

data centered;
 set problem81;
 q = quet - 3.4410938 ; a = age -  53.25 ;
 s = smk -  0.53125 ; aq=a*q;
 as = a*s; qs=q*s; aqs=a*q*s;

/* Results like those in the book */
/* Too much collinearity among these variables */
proc reg corr data=problem81;
 model sbp = age quet smk aq as qs aqs / selection=rsquare cp mse adjrsq;

proc reg corr data=centered;
 model sbp = a q s aq as qs aqs / selection=rsquare cp mse adjrsq;
 model sbp = a q s aq as qs aqs / selection=forward;
 model sbp = a q s aq as qs aqs / selection=backward;
 model sbp = a q s aq as qs aqs / selection=stepwise;
run;
quit;