/* ---------------------------------------------------------------
 program: heart0-v92.sas
 xref:    Stanford Heart Transplant Data
 input:   heart2.dat
 output:
 does:    Time dependent covariate
--------------------------------------------------------------- */;

OPTIONS PS=68 LS=120 PAGENO=1 NODATE NOCENTER ERRORS=3;

filename INF "h:\bios180\coursepack\SAS-unc-workshop-2008\heart2.dat";

*******************************************************;
data A;
  infile INF delimiter=':';
  input id year age delta survtime surg
        trans waittime match1 match2 match3;
run;

**********************************************************;
** Use transplant status as a time dependent covariate         ;
**********************************************************;
proc phreg data=A;
  model survtime*delta(0)=xtrans;
  if (waittime>survtime or waittime=.)
        then xtrans=0;
        else xtrans=1;
run;

*****************************************************;
** Now compare this to non-time-dependent estimate   ;
** of the RR associated with transplant        ;
*****************************************************;
proc phreg data=A;
  model survtime*delta(0)=trans;
run;

********************************************************************;
** This model indicates that a heart transplant is very protective. ;
** Why is the difference from the TDC model?  Which is better?         ;
**********************************************8*********************;