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Re: st: p-values for K-M point survival estimates using sts list

From   Steve Samuels <>
Subject   Re: st: p-values for K-M point survival estimates using sts list
Date   Wed, 25 Aug 2010 20:09:01 -0400


Cynthia, if S(t) is the KM estimate, the CIs are based on
log(-log(S(t)), which removes range restrictions. The SE itself is a
function of S(t) and so does not make a good denominator.

Let S = S(t)

vl = var(log S)= (1/S^2)x var(S)

 w = log(-log(S))
var(w) = vl/(logS)^2

Base the test of difference on w.


Steven Samuels
18 Cantine's Island
Saugerties NY 12477
Voice: 845-246-0774
Fax:    206-202-4783

On Wed, Aug 25, 2010 at 11:41 AM, Bell, Cynthia
<> wrote:
> The "sts list" command provides point estimates, std errors, and confidence intervals at exact times during my observation period. I prefer confidence intervals to compare, say, 10-year survival estimates between groups but a journal requested p-values comparing group point estimates at specific time points. Is this possible in Stata? If not, it shouldn't be complicated to compute a p-value given a distribution for the K-M survival point estimate and the standard error, right?
> Thanks very much,
> Cynthia Bell
> Division of Pediatric Nephrology and Hypertension
> University of Texas-Houston, Medical School

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