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R: st: R: reporting time dependent covariates in cox regression


From   "Carlo Lazzaro" <carlo.lazzaro@tin.it>
To   <statalist@hsphsun2.harvard.edu>
Subject   R: st: R: reporting time dependent covariates in cox regression
Date   Fri, 4 Sep 2009 11:29:48 +0200

Dear Moleps,
in the first part of my previous reply I misunderstood that, from the very start of your message, you focused on tvc and not on proportional hazard condition only.

<Cleves is a good book, [...] they dont either give any clues as to how results with -tvc-should be presented.>

I agree with you that more examples can help readers. Hopefully this might be improved in the next edition of this helpful textbook. 
However, at pag 169 of the revised edition (par 10.5.1), authors report a brief description of the output of

. stcox protect, tvc(init_drug_level) texp(exp(-0.35*_t))

and highlight that

"The hazard ratio 0.8848 is now interpreted as those with higher drug levels in their bloodstreams have a lower risk of having a hip fracture"  

as far as the time-varying variable is concerned.

As a temptative hint, I was wondering whether the same approach  - that is, splitting the Cox regression table to allow for constant-with-time variables (rh) and time-varying-variables (t) Hazard Ratios to be separately reported; describing in the Results section of your research report what causes your Hazard Ratios to differ - may match with your research aims.

Sorry I cannot be more helpful. 

Kind Regards and All the Best for your research project,
Carlo
-----Messaggio originale-----
Da: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] Per conto di moleps islon
Inviato: venerdì 4 settembre 2009 9.43
A: statalist@hsphsun2.harvard.edu
Oggetto: Re: st: R: reporting time dependent covariates in cox regression

Appreciate your efforts, Carlo. However Lindholt et al had only
dichotomised before and after x yrs, not the -tvc-option in stata. I
agree that Cleves is a good book, but a little short on the practical
examples-and they dont either give any clues as to how results with
-tvc-should be presented.

Regards,
M


On Fri, Sep 4, 2009 at 7:59 AM, Carlo Lazzaro<carlo.lazzaro@tin.it> wrote:
> Dear Moleps,
> As far as a part of your query is concerned
>
> <I still havent even seen anyone report whether PH assum_p_tions have been
> met, so I cant really find any articles to copy>.
>
> I would refer you to the following article:
>
> Jes S Lindholt, Svend Juul, Helge Fasting and Eskild W Henneberg
> Screening for abdominal aortic aneurysms: single centre randomised
> controlled trial. BMJ, doi:10.1136/bmj.38369.620162.82. (Particularly,
> Statistical analyses paragraph).
>
> For further details on Survival Analysis topics, I will recommend you to
> take a look at:
> Cleves MA, Gould WG, Gutierrez R. An Introduction To Survival Analysis Using
> Stata. Revised edition. College Station: StataPress, 2004; [ST] Stata
> manual. Survival analysis and epidemiological table. Release 9
>
> Two other relevant contributors of the Statalist - Maarten Buis
> (http://home.fsw.vu.nl/m.buis/)  and Stephen Jenkins
> (http://www.iser.essex.ac.uk/teaching/degree/stephenj/ec968/index.php.)
> published really interesting papers as well as teaching-notes on Survival
> Analysis.
>
> HTH and Kind Regards,
>
> Carlo
>
> -----Messaggio originale-----
> Da: owner-statalist@hsphsun2.harvard.edu
> [mailto:owner-statalist@hsphsun2.harvard.edu] Per conto di moleps islon
> Inviato: giovedě 3 settembre 2009 22.32
> A: statalist@hsphsun2.harvard.edu
> Oggetto: st: reporting time dependent covariates in cox regression
>
> Dear listers,
> What is a good way to report time-dependent covariates in a
> multi-variate cox table? In my field of research I still havent even
> seen anyone report whether PH assumtions have been met, so I cant
> really find any articles to copy.
>
> I´m thinking in the lines of reporting an extra line beneath the main
> effect in parenthesis for the significant time-dependent variables in
> a table. Anyone have any experience in this?
>
> Also-how would you interpret a significant interaction between age and
> treatment that is also time-dependent?
>
>
> Regards,
> M
>
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