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Re: st: R: compare median survival times? (flag: Stata 9.2/SE)

From   Ronan Conroy <>
To   "" <>
Subject   Re: st: R: compare median survival times? (flag: Stata 9.2/SE)
Date   Fri, 11 Jun 2010 12:23:28 +0100

On 11 Meith 2010, at 08:44, Carlo Lazzaro wrote:

Marty may want to customize what follows:
--------- code begins-----------
sysuse cancer.dta, clear
stset studytime, failure(died==1)
sts test drug if r(p50), logrank
-------- code ends---------------

But doesn't this just compare the survival function in those in whom the median survival time is definable?

The hypothesis is a very peculiar one indeed: specifically, that the 50th percentile of the survival function differs between two groups. I don't know why anyone would formulate this hypothesis (why the 50th centile and not some other quantile? why ignore differences at other quantiles?) but it's a tricky one to try to test. It seems to me that you would need interval quantile regression, something whose complexities cause one to have to sit down and drink a glass of water.

Or am I missing something?

Ronan Conroy
Royal College of Surgeons in Ireland
Epidemiology Department,
Beaux Lane House, Dublin 2, Ireland
+353 (0)1 402 2431
+353 (0)87 799 97 95
+353 (0)1 402 2764 (Fax - remember them?)

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