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st: Polytomous vs "regular" unconditional logistic regression


From   Roger Milne <rlm@unimelb.edu.au>
To   statalist@hsphsun2.harvard.edu
Subject   st: Polytomous vs "regular" unconditional logistic regression
Date   Fri, 28 Nov 2003 12:41:20 +1100

Hi,

I don't understand why I get different estimates (ignoring standard errors) from the following two models:

1. Multivariate polytomous logistic regression, with outcome categories 0, 1 and 2 (with ", basecategory(0)")
2. Two separate multivariate (same covariates) "regular" logistic regression models:
(i) with ", if outcome~=2"
(ii) with ", if outcome~=1"

The "coeff" estimates are very different (eg. -1.52 vs. -1.06)

For the univariate case, I get the same estimates from 1 and 2, but they start to "diverge" as soon as I add an additional covariate.

Thanks,

Roger Milne.

Roger Milne
Research Fellow
Centre for Genetic Epidemiology
University of Melbourne
Tel: +613 8344 0803
Fax: +613 9349 5815
email: rlm@unimelb.edu.au

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