options pagesize=47 linesize=64;
filename grafout 'l07.ps';
goptions device=pslmono gsfname=grafout gsfmode=append;
data larynx; infile 'larynx.dat';
   input stage time age year status;
   year=year-74; stg2=0; stg3=0; stg4=0;
   if stage=2 then stg2=1;
   if stage=3 then stg3=1; if stage=4 then stg4=1; run;
data smlar; set larynx; if age<60 then; else delete; run;
proc phreg data=smlar; 
   title1 'Small Data Set Example showing Infinite Estimate';
   model time*status(0)=age year stg2 stg3 stg4; run;
/* Calculate baseline hazard for individual 50 years old, in
1979.  Note that year is defined as years since 1974.    */
data friend; input age year; stg2=0; stg3=0; stg4=0; cards;
50 5
; run;
proc phreg data=larynx noprint;
   model time*status(0)=age year stg2 stg3 stg4;
   baseline out=baseout survival=s covariates=friend/nomean;
   run;
proc gplot data=baseout; title1 'Baseline survival function';
   symbol1 i=stepljs; plot s*time; run;
/* Commands to do model selection .*/
proc phreg data=larynx; 
   model time*status(0)=stg2 stg3 stg4 age year/
      selection=score; run;
/* To do model selection using AIC, we would have to fit all
models separately:
proc phreg data=larynx;
   model time*status(0)=stg2 stg3 stg4 ; run;
proc phreg data=larynx; 
   model time*status(0)=age ; run;
proc phreg data=larynx; 
   model time*status(0)=year; run;
proc phreg data=larynx;
   model time*status(0)=stg2 stg3 stg4 age ; run;
proc phreg data=larynx;
   model time*status(0)=stg2 stg3 stg4 year; run;
proc phreg data=larynx; 
   model time*status(0)=age year; run;
proc phreg data=larynx;
   model time*status(0)=stg2 stg3 stg4 age year; run;*/