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st: Increasing variance of dependent variable, logit, inter-rater agreement


From   "Supnithadnaporn, Anupit" <gtg065t@mail.gatech.edu>
To   statalist <statalist@hsphsun2.harvard.edu>
Subject   st: Increasing variance of dependent variable, logit, inter-rater agreement
Date   Thu, 26 Feb 2009 20:30:05 -0500 (EST)

Dear Stata List members,

I am trying to learn what factors might determine the inter-rater agreement 
between the two tests of the same subject using different technologies. One technology measures the characterisitcs of a subject and gives the result of 
pass-fail (y1). The other technology gives the interval measurement 
(y2a) and the pass-fail (y2b) can be obtained using certain threshold.

My simple idea is to use the logit regression of a dependent variable 
called 'agree' which takes value 1 if both tests yield the same results
(y1=y2b) otherwise 0.  

agree = f(age, x1,x2,x3,...)

The problem is that as 'age' increases, I know that the variance of y2a
also increases. This is due to the nature (deterioration) of the subject
itself. Given that the quality of the instrument measuring y2a is constant,
how should I take into account the increasing variance of y2a in my model?

Thank you,

Anupit


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