options ls = 78;
libname fu '../../sdata';
data fu.gastric;
infile '../../data//gastric.dat' firstobs = 2;
input pid 1-3 os 8-12 censor 15 treat 20;

/* generating Figures 11.5 and 11.6 */
proc lifetest plot=(s, lls);
        time os * censor(0);
        strata treat;

proc phreg;
        model os*censor(0) = x1 x2 x3 x4/risklimits;
        if 0< os <= 360  then x1 = treat; else x1 = 0;
        if 360 < os <= 720  then x2 = treat; else x2 = 0;
        if 720 < os <= 1080  then x3 = treat; else x3 = 0;
        if os > 1080  then x4 = treat; else x4 = 0;
run;