> > 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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