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st: How to adjust for center ?


From   keioli@tiscali.ch
To   statalist@hsphsun2.harvard.edu
Subject   st: How to adjust for center ?
Date   Mon, 27 Mar 2006 11:47:09 +0200

Dear all
I performed a longitudinal GEE model with an exchangeable correlation and
a logit link. 
The outcome was visit(y/n) in a defined period of 12 months and each person
contributed a maximum of three observations to the estimation depending
if that person was seen in every one of three periods or not.

The format of the data is the following:
Id   Visit_yn    age  other covariates
1     0
1     0
1     1
2     1
2     0

My original code:

xi: xtgee visit_yn age other_covariates, i(id) t(t_exam) fam(bin) link(logit)
corr(exch)


I have now seen in a univariate analysis that there are substantial differences
among the 6 centers and would like to adjust for this potential correlation
within people of the same center. I guess that a multilevel mixed model
would be suitable with center as the random effect.

I?m however not sure how this can be performed in Stata (probably using
glamm?)

I thought of something like 

glamm visit_yn age other_covariates, i(center) link(logit) family(bin)

This does however not include the longitudinal design.
Could anybody help me with this?

Best regards

Oli











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