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;
 quet_age = quet*age;
 quet_smk = quet*smk;
 age_smk = age*smk;

proc reg corr;
 model sbp = age quet smk quet_smk quet_age age_smk / collin;

proc means;
 var quet age smk;
run;

data centered;
 set problem81;
 quetc = quet - 3.4410938 ;
 agec = age -  53.25 ;
 smkc = smk -  0.53125 ;
 quet_smk = quetc*smkc;
 quet_age = quetc*agec;
 age_smk = agec*smkc;

proc reg corr;
 model sbp = agec quetc smkc quet_smk quet_age age_smk / collin;
run;
quit;