* Researchers randomized 44 patients diagnosed with hepatitis and randomized them to prednisolone or placebo (TREAT)
* time= the time in months from point of randomization to death or censoring
* censor: 1= dead, 0=censored
;
options nofmterr;
libname paul "I:\BMTRY748\mulugeta\sas examples";

data hepa;
input time censor treat;
datalines;
2 1 1
6 1 1
12 1 1
54 1 1
56 0 1
68 1 1
89 1 1
96 1 1
96 1 1
125 0 1
128 0 1
131 0 1
140 0 1
141 0 1
143 1 1
145 0 1
146 1 1
148 0 1
162 0 1
168 1 1
173 0 1
181 0 1
2 1 0
3 1 0
4 1 0
7 1 0
10 1 0
22 1 0
28 1 0
29 1 0
32 1 0
37 1 0
40 1 0
41 1 0
54 1 0
61 1 0
63 1 0
71 1 0
127 0 0
140 0 0
146 0 0
158 0 0
167 0 0
182 0 0
; 
run;
proc format;
   value Rx  1='prednisolone' 0='control';
   run;
/*Plot KM curve*/
goptions reset=all;
proc lifetest data=hepa    plots=(s, ls) graphics censoredsymbol=none;
time time*censor(0); 
title 'Kaplan-Meier plot of survivorship';
symbol v=none ; 
run;

proc lifetest data= hepa plots=(s) graphics censoredsymbol=none;
time time*censor(0); 
	title 'cumulative hazard functions by group';
	strata treat; 
	format treat rx. ;
run; quit;

proc lifetest data=hepa plots=(s, ls, lls) graphics censoredsymbol=none;
time time*censor(0); 
	title 'cumulative hazard functions by group';
	strata treat; 
	format treat rx. ;
run; quit;

* parametric regression;
proc lifereg data=hepa;
	model time*censor(0)= treat /dist=exponential;
run;

proc lifereg data=hepa;
	model time*censor(0)= treat /dist=weibull;
run;

proc lifereg data=hepa;
	model time*censor(0)= treat /dist=lnormal;
run;

*semi-parametric regression;
proc phreg data=hepa;
model time*censor(0)= treat;
run;

** When there are ties ****;
/**Do not specify ties**/
proc phreg data=hepa;
model time*censor(0)=treat / risklimits; 
title 'Cox model -- ties';
run;

/**Efron**/
proc phreg data=hepa;
model time*censor(0)=treat  / ties=efron risklimits; 
title 'Cox model—ties=efron';
run;
/**Exact**/
proc phreg data=hepa;
model time*censor(0)=treat  / ties=exact risklimits; 
title 'Cox model —ties=exact';
run;
/**Discrete**/
proc phreg data=hepa;
model time*censor(0)=treat  / ties=discrete risklimits; 
title 'Cox model —ties=discrete';
run;