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RE: st: Survival analysis: Interpretation of Cox regression


From   "Maarten Buis" <M.Buis@fsw.vu.nl>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: Survival analysis: Interpretation of Cox regression
Date   Mon, 2 Jan 2006 14:14:57 +0100

> > 2) How can I verify if survivor function at a particular time
> > (e.g. 5 years) are statistically different?
>
> It is an assumption of the Cox model that the hazard of group one is always proportional to the
> hazard of the reference category. So if you find a hazard ratio of 1.4, than the hazard of group
> one is always 40% higher than the hazard of the reference category. If this effect is significant
> than the groups are, by assumption, always significantly different.

More about testing the proportionality assumption can be found on:
http://www.ats.ucla.edu/stat/sas/faq/test_proportionality.htm and 
http://www.ats.ucla.edu/stat/stata/seminars/stata_survival/default.htm

HTH,
Maarten

-----------------------------------------
Maarten L. Buis
Department of Social Research Methodology 
Vrije Universiteit Amsterdam 
Boelelaan 1081 
1081 HV Amsterdam 
The Netherlands

visiting adress:
Buitenveldertselaan 3 (Metropolitan), room Z214 

+31 20 5986715

http://home.fsw.vu.nl/m.buis/
-----------------------------------------





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