LIBNAME DATADIR '/afs/ir.stanford.edu/class/stats262/WWW/sas';

DATA WHAS_MOD;
    SET DATADIR.WHAS;
    TIME=LENFOL;
    IF YRGRP^='1975 & 1978' THEN DELETE;
    IF FSTAT='Dead' THEN CENSOR=1;
    ELSE CENSOR=0;
    IF SEX='Male' THEN SEX_NUM=1;
    ELSE SEX_NUM=0;
    IF SHO='YES' THEN SHO_NUM=1;
    ELSE SHO_NUM=0;
    IF CHF='YES' THEN CHF_NUM=1;
    ELSE CHF_NUM=0;
RUN;

PROC PHREG DATA=WHAS_MOD;
    MODEL LENFOL*CENSOR(0) = AGE SEX_NUM CPK SHO_NUM CHF_NUM LENSTAY / SELECTION=SCORE BEST=3;
RUN;

PROC PHREG DATA=WHAS_MOD;
    MODEL LENFOL*CENSOR(0) = AGE SEX_NUM CPK SHO_NUM CHF_NUM LENSTAY / SELECTION=STEPWISE DETAILS;
RUN;

PROC PHREG DATA=WHAS_MOD;
    MODEL LENFOL*CENSOR(0) = AGE SEX_NUM CPK SHO_NUM CHF_NUM LENSTAY / SELECTION=BACKWARD DETAILS;
RUN;

PROC PHREG DATA=WHAS_MOD;
    MODEL LENFOL*CENSOR(0) = AGE SEX_NUM CPK SHO_NUM CHF_NUM LENSTAY / SELECTION=FORWARD DETAILS;
RUN;