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Re: st: Kaplan-Meier curve does not reach tmax


From   "Svend Juul" <SJ@SOCI.AU.DK>
To   <statalist@hsphsun2.harvard.edu>
Subject   Re: st: Kaplan-Meier curve does not reach tmax
Date   Fri, 2 Mar 2007 20:46:57 +0100

Tobias wrote:
 
I have the following problem: I want to plot patients'
survival from 0 to 5 (sts graph). I have only 5 patients
with follow-up of more than 5 years, so I want to restrict
the Kaplan-Meier curve to 5 years.
 
When I use the tmax(5) function, the curve ends at
approximately 4.5 years. This is the timepoint, when the
last patient with follow-up of less than 5 years was censored. 
Is there a way to plot the curve exactly to 5 years?
Otherwise, it appears that the follow-up ends at 4.5 years.
----------------------------------------------------------------
 
I believe you hit an inconsistent Stata behavior. The following 
gives a curve that ends at time 20:
   clear
   sysuse cancer
   stset studytime , failure(died=1)
   sts graph , tmax(20)
 
So does the following:
   clear
   sysuse cancer
   drop if died==1 & studytime>19
   stset studytime , failure(died=1)
   sts graph , tmax(20)
 
But this one ends at time 19:
   clear
   sysuse cancer
   drop if died==0 & studytime>19
   stset studytime , failure(died=1)
   sts graph , tmax(20)
 
So, apparently the time of the last censoring is considered
the end of information, even if events do occur later than that.
 
Until this inconsistency has been corrected: You might use
   sts generate
to create coordinates for the graph. Hint: Points should
be connected "stairstep" with 
   ... , connect(J)
 
See [G] connectstyle or -help connectstyle-
 
Hope this helps
Svend
 
________________________________________________________ 
 
Svend Juul
Institut for Folkesundhed, Afdeling for Epidemiologi
(Institute of Public Health, Department of Epidemiology)
Vennelyst Boulevard 6 
DK-8000 Aarhus C,  Denmark 
Phone, work:  +45 8942 6090 
Phone, home:  +45 8693 7796 
Fax:          +45 8613 1580 
E-mail:       sj@soci.au.dk 
_________________________________________________________ 

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