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Re: st: Including age as covariate or using age-stratified estimates in stcox


From   roland andersson <rolandersson@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Including age as covariate or using age-stratified estimates in stcox
Date   Fri, 1 Oct 2010 16:44:06 +0200

Raoul

Thank you for this comment.

I had time since operation as analysis time and used age at operation
(and age squared) as covariates and compared with age as strata. I
obtained almost identical results in both cases.

After your comment I tried attained age as analysis time and compared
age at operation (and age squared) with age at operation (in decades)
as strata. I now obtain almost identical results for both but the
estimates differ somewhat depending on the choice of analysis time.

I think I should use attained age as analysis time and age at
operation as strata (the stphplot shows that the hazard is not
proportional for age at operation). Am I doing the right thing?

Roland



2010/10/1 raoul reulen <r.c.reulen@gmail.com>:
> Roland,
>
> Do you mean attained age or age at appendectomy? I suspect that the
> proportional hazard assumption was not satisfied for age. Did you
> check for this?
>
> Raoul
>
> On 1 October 2010 07:00, roland andersson <rolandersson@gmail.com> wrote:
>> I am analysing cause-specific mortality after appendectomy. Mortality
>> is strongly related to age as is exposure to different morbidities.
>> The hazard therefore varies according to age. I get substantially
>> different results if I use stcox with strata(age) or include age and
>> age2 as covariates. Can you help me understand the difference and the
>> correct use of stratified anlysis versus including the variables as
>> covariates.
>>
>> Roland Andersson, MD, PhD
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