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;
 if smk = 0 then smk1 = -1;
 if smk = 1 then smk1 = 1;

proc sort; by smk;
proc ttest;
 var sbp;
 class smk;

proc reg;
 model sbp = smk;
 model sbp = smk1;


data problem3;
 infile 'i:\.www\datasets502\EX1403.DAT' firstobs=2 dlm='09'x;
 input country $ x y;
 if country = "RICH" then z=0;
 if country = "POOR" then z=1;
 x_z = x*z;

proc sort; by z;
symbol1 v=circle i=rl;
symbol2 v=square i=rl line=2;
proc gplot;
 plot y*x = z;

proc reg;
 model y = x;
 by z;
proc reg;
 model y = x z x_z / ss1;

run;
quit;