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st: Re: offsets


From   Roger Newson <roger.newson@kcl.ac.uk>
To   statalist@hsphsun2.harvard.edu
Subject   st: Re: offsets
Date   Tue, 22 Jul 2003 13:31:22 +0100

At 12:38 22/07/03 +0100, Paul Silcocks wrote:
Is it possible to have more than one offset in a logistic (or other)
regression model?

Specifically I have an ordered categorical variable representing levels of a
clinical scoring system.  I want to see what the added value of a new
variable is, but I want to constrain the regression coefficients for the
levels of the categorical variable to be unity.

these are approaches I tried (dep is the ordered categorical variable) -
none of which work:

xi: logistic outcome1 i.dep ageatmi, offset(i.dep)

logistic outcome1  _Idep_1 _Idep_2 _Idep_3 _Idep_4 ageatmi, offset( _Idep_1
_Idep_2 _Idep_3 _Idep_4)

logistic outcome1  _Idep_1 _Idep_2 _Idep_3 _Idep_4 ageatmi, offset( _Idep_1)
offset( _Idep_2) offset( _Idep_3) offset( _Idep_4)

Any thoughts?
I think the way to go is to add all your multiple offsets together to make one grand offset, and use that as your -offset()- option. This will fit the correct model.

I hope this helps.

Roger


--
Roger Newson
Lecturer in Medical Statistics
Department of Public Health Sciences
King's College London
5th Floor, Capital House
42 Weston Street
London SE1 3QD
United Kingdom

Tel: 020 7848 6648 International +44 20 7848 6648
Fax: 020 7848 6620 International +44 20 7848 6620
or 020 7848 6605 International +44 20 7848 6605
Email: roger.newson@kcl.ac.uk
Website: http://www.kcl-phs.org.uk/rogernewson

Opinions expressed are those of the author, not the institution.

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