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st: RE: Re: Kappa for multiple raters and paired body parts


From   Garry Anderson <g.anderson@unimelb.edu.au>
To   statalist@hsphsun2.harvard.edu
Subject   st: RE: Re: Kappa for multiple raters and paired body parts
Date   Tue, 23 Nov 2010 12:18:50 +1100

Many thanks Joseph for your helpful siggestions.

Best wishes, Garry
 

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Joseph
Coveney
Sent: Saturday, 20 November 2010 7:43 PM
To: statalist@hsphsun2.harvard.edu
Subject: st: Re: Kappa for multiple raters and paired body parts

Garry Anderson wrote:

I wish to estimate a single kappa (SE or 95%CI) when there are 4 raters
that each rate the left and right eyes of about 150 patients. The
response for each eye is binary. Estimation of kappa (SE) can be done
separately for the left eye and the right eye using -kap- or -kapci-,
however I am unsure as to how to include both eyes and take account of
the non-independence of eyes. Schouten (1993) describes the methodology
for two raters.

Schouten HJA (1993) Estimating kappa from binocular data and comparing
marginal probabilities. Statistics in Medicine 12: 2207-2217.

Any suggestions would be appreciated.

------------------------------------------------------------------------
--------

Well, kappa for binary scores is an intraclass correlation coefficient
(ICC).  
How about using -xtmelogit- to fit a cross-classified random-effects
model to the data with i.side (right or left eye) as a fixed effect, and
then use the patients' and raters' variance components, along with the
logistically distributed residual (pi^2 / 3), to compute the ICC
(patients' divided by the sum of patients', raters' and residual)?  You
can get the (transformed) variance components from the parameter vector,
e(b).  I'm guessing that bootstrapping is the best bet for the
confidence interval.  But -nlcom- is also worth looking into for this.

Joseph Coveney


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