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Re: st: cluster v. shared frailty


From   May Boggess <mboggess@stata.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: cluster v. shared frailty
Date   12 Aug 2003 13:01:38 -0500

Sarah A. Mustillo <smustillo@psych.duhs.duke.edu> asked about the
difference between a shared frailty model and the -cluster- option when
using -stcox-:

> I am running a cox model on data that are clustered by study site. 

> "One solution would be to fit a standard Cox model, adjusting the standard
> errors of the estimated hazard ratios to account for the possible
> correlation by specifying cluster(patient).
> 
> Alternatively, one can model the correlation by assuming that the
> correlation is the result of a latent patient-level effect, or frailty.
> That is, rather than fitting a standard model and specifying
> cluster(patient), fit a frailty model by specifying shared(patient)."

Sarah asks:
> How does one decide which method to use?

I want to say "go with the shared frailty", because the -cluster- option
is not fitting a more sophisticated model; it's just giving you a more
generous standard error estimate. My instinct says to me that building
the correlation within study-site into the model has to be better. 

BUT that is only good advice IF shared frailty is the correct model.
Thus, to compare the models, I would look at goodness-of-fit tests and
the residuals (as suggested in chapter 11 of Stata's Survival Analysis
book: http://www.stata.com/bookstore/saus.html). 

Also, I found some similar questions by searching the Statlist archive  
(http://www.stata.com/statalist/archive/)

Here are two repsonses on the same subject:
http://www.stata.com/statalist/archive/2002-06/msg00450.html

http://www.stata.com/statalist/archive/2003-05/msg00431.html

-- May
mboggess@stata.com



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