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st: RE: marginal coding of dummy varaible

From   "Maarten Buis" <[email protected]>
To   <[email protected]>
Subject   st: RE: marginal coding of dummy varaible
Date   Wed, 26 Apr 2006 17:14:55 +0200

Val�rie Jooste:
In this coding scheme all parameters (including the one left out) 
add up to zero. If you have 5 groups, you will get 4 parameters
and the fifth parameter is 

Maarten L. Buis
Department of Social Research Methodology 
Vrije Universiteit Amsterdam 
Boelelaan 1081 
1081 HV Amsterdam 
The Netherlands

visiting adress:
Buitenveldertselaan 3 (Metropolitan), room Z214 

+31 20 5986715

-----Original Message-----
From: [email protected] [mailto:[email protected]]On Behalf Of Val�rie Jooste
Sent: woensdag 26 april 2006 17:04
To: [email protected]
Subject: st: marginal coding of dummy varaible

I am trying to perform a logistic regression without defining a reference
group for the independent discrete variables:
I am intending to determine the ratio of the odds of each of the J levels of
a discrete variable to the average odds (geometric mean of all levels). For
that matter, instead of using the classical reference coding, I followed the
"marginal method". I created dummy variables using the marginal coding:
It means that, instead of coding the jth dummy variable 1 if the discrete
variable is at the jth level and 0 if the discrete variable is at any other
level, I coded the jth dummy variable -1 for the first level, 1 for the jth
level and 0 for the others.
This works beautifully and avoids having a group as reference but brings
another (big) problem: the 1st level doesn't appear at all in results (not
even as reference...).
How can I estimate a coefficient for level 1?

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