# Re: st: Cox Regression

 From Timothy.Mak@iop.kcl.ac.uk To statalist@hsphsun2.harvard.edu Subject Re: st: Cox Regression Date Tue, 23 Aug 2005 09:33:45 +0100

```So what are the assumptions that I should look out for?
Any more answers on the other parts of my question?

Thanks again.
Tim

Marcello Pagano <pagano@hsph.harvard.edu>
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19/08/2005 18:19
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Re: st: Cox Regression

I would not think so.  You are basing your decision of non-significance
on a test whose
validity is based on an assumption.  If the assumption is not valid,
then neither is the test.
Think of a simple analogy with linear models.  Suppose the relation
between y and x is a
V-shaped one.  The coefficient of x in a linear model may well test out
to zero. That would
not mean that the relationship is linear.

m.p.

Timothy.Mak@iop.kcl.ac.uk wrote:

>Hi when performing a Cox regression with or without a time dependent
>covariate, is a non-significant result in a -stphtest- generally enough
>evidence for the assumption of proportional hazard?
>
>If I have multiple covariates, but I'm only interested in one, is it
>enough to check only the proportional hazard assumption of the variable
>I'm interested in? ie using the stphtest, detail, rather than stphtest?
>
>Lastly, is it better to use stphtest log, or one of the other option
>rather than stphtest if hazard increases over time and most of my
>participants 'died' early during the observation period?
>
>Thanks a lot for any answer.
>
>Tim
>
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```