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st: intraclass corr in hierachical mixed model


From   "Michael DeLorenzo" <DELORM@mmc.org>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: intraclass corr in hierachical mixed model
Date   Thu, 18 Aug 2005 10:13:20 -0400

The Stata manual suggests that the intraclass correlation coef (ICC) in a logistic hierarchical mixed model ('multilevel' mixed model) can be computed as 

sigma_panel/(sigma_panel + 1) 

after running the xtlogit command with appropriate data. For instance see p 378 ref volume Su-Z for release 6.

I am new to Stata, and from all other work, I would expect   pi^2/3  rather than the 1 in the denominator for the ICC. This because the error variance on the logistic scale is pi^2/3.  I would accept the 1 if the link function was probit rather than logit.

Does Stata use a constraint I am unaware of contained in the quadrature calucaltion? It appears it might from formula on page 381 of manual referred to above.  Or am I just missing something?

Thanks to anyone who knows.

Michael DeLorenzo
Maine Medical Center


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