topic How to get confidence interval for failure rate in proc lifetest in Statistical Procedures

How to get confidence interval for failure rate in proc lifetest

xinjian — Mon, 04 Apr 2016 21:35:25 GMT

Hi Everyone,

I am doing a survival analysis using PROC lifetest. I want to get failure rate and its confidence interval at 12 month.below is my syntex and output:

proc lifetest data = ll atrisk;

strata intervene;

time month*status(0);

run;

Part of output:

Month		Number at risk	observed event	survival	Failure	survival SE
0		11	0	1	0	0
2.4658		11	1	0.9091	0.0909	0.0867
7.726		10	1	0.8182	0.1818	0.1163
8.1205		9	1	0.7273	0.2727	0.1343
11.1781	*	8	0	.	.	.
12.3288	*	7	0	.	.	.
12.4603	*	6	0	.	.	.
12.5589	*	5	0	.	.	.
17.3589		4	1	0.5455	0.4545	0.1869
23.9014	*	3	0	.	.	.
24.4603	*	2	0	.	.	.

Is there a way to dirrectly get failure rate and its 95%confidence interval?

Many Thanks!

Re: How to get confidence interval for failure rate in proc lifetest

Reeza — Mon, 04 Apr 2016 21:52:27 GMT

Use outsurv and timelist to specify your intervals.

Note that KM is non parametric so if there isn't an estimate for your specific time point it picks the nearest time with an estimate.

Re: How to get confidence interval for failure rate in proc lifetest

xinjian — Tue, 05 Apr 2016 01:59:59 GMT

Hi Reeza,

Thanks for your suggestion, I am still not get failure rate and its CI. Here is my syntax:

proc lifetest data = ll atrisk;

time month*status(0);

strata intervene ;

survival out=out1 ;

run;

proc print data=out1 noobs;

where 3 <=month<=12 & conftype~="";

run;

and my output:

intervene	month	_CENSOR_	SURVIVAL	CONFTYPE	SDF_LCL	SDF_UCL	STRATUM
Intervene	7.72602	0	0.81818	LOGLOG	0.44743	0.95116	1
Intervene	8.12054	0	0.72727	LOGLOG	0.37079	0.90283	1

Can you help me to get failure rate and its CI?

Thanks

Re: How to get confidence interval for failure rate in proc lifetest

Reeza — Tue, 05 Apr 2016 04:10:34 GMT

Failure = 1 - Survival.

You can calculate 1- number to get the failure values from the OUTSURV table.

Regardless here's the way to get SAS to do it, first you need to create the failure plot and specify cl options. Then use the graph to get the values using ODS OUTPUT. A worked example follows.

I'm also not sure why your code works. There's no survival statement that I can see in the documentation, so it should create an error.

  proc format;
      value risk 1='ALL' 2='AML-Low Risk' 3='AML-High Risk';
    
   data BMT;
      input Group T Status @@;
      format Group risk.;
      label T='Disease Free Time';
      datalines;
   1 2081 0 1 1602 0 1 1496 0 1 1462 0 1 1433 0
   1 1377 0 1 1330 0 1  996 0 1  226 0 1 1199 0
   1 1111 0 1  530 0 1 1182 0 1 1167 0 1  418 1
   1  383 1 1  276 1 1  104 1 1  609 1 1  172 1
   1  487 1 1  662 1 1  194 1 1  230 1 1  526 1
   1  122 1 1  129 1 1   74 1 1  122 1 1   86 1
   1  466 1 1  192 1 1  109 1 1   55 1 1    1 1
   1  107 1 1  110 1 1  332 1 2 2569 0 2 2506 0
   2 2409 0 2 2218 0 2 1857 0 2 1829 0 2 1562 0
   2 1470 0 2 1363 0 2 1030 0 2  860 0 2 1258 0
   2 2246 0 2 1870 0 2 1799 0 2 1709 0 2 1674 0
   2 1568 0 2 1527 0 2 1324 0 2  957 0 2  932 0
   2  847 0 2  848 0 2 1850 0 2 1843 0 2 1535 0
   2 1447 0 2 1384 0 2  414 1 2 2204 1 2 1063 1
   2  481 1 2  105 1 2  641 1 2  390 1 2  288 1
   2  421 1 2   79 1 2  748 1 2  486 1 2   48 1
   2  272 1 2 1074 1 2  381 1 2   10 1 2   53 1
   2   80 1 2   35 1 2  248 1 2  704 1 2  211 1
   2  219 1 2  606 1 3 2640 0 3 2430 0 3 2252 0
   3 2140 0 3 2133 0 3 1238 0 3 1631 0 3 2024 0
   3 1345 0 3 1136 0 3  845 0 3  422 1 3  162 1
   3   84 1 3  100 1 3    2 1 3   47 1 3  242 1
   3  456 1 3  268 1 3  318 1 3   32 1 3  467 1
   3   47 1 3  390 1 3  183 1 3  105 1 3  115 1
   3  164 1 3   93 1 3  120 1 3   80 1 3  677 1
   3   64 1 3  168 1 3   74 1 3   16 1 3  157 1
   3  625 1 3   48 1 3  273 1 3   63 1 3   76 1
   3  113 1 3  363 1
   ;
 

proc lifetest data = bmt atrisk plots=survival(failure cl);
time T*status(0);
strata group ;
ods output failureplot=want;
run;

Re: How to get confidence interval for failure rate in proc lifetest

xinjian — Tue, 05 Apr 2016 15:41:04 GMT

Reeza,

Thanks for your help!