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st: RE: RE: marginal coding of dummy varaible

From   Valérie Jooste <>
To   <>
Subject   st: RE: RE: marginal coding of dummy varaible
Date   Thu, 27 Apr 2006 15:48:43 +0200

Maarten, all
Thank you for your precious help. It makes sense and I am very glad that it
is so easy. Could you please confirm if I'm right by then calculating
SE(_b[group1]) using the property of variance :
Thank you

-----Message d'origine-----
De :
[] De la part de Maarten Buis
Envoyé : mercredi 26 avril 2006 17:15
À :
Objet : st: RE: marginal coding of dummy varaible

Valérie 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), Xoom Z214 

+31 20 5986715

-----Original Message-----
[]On Behalf Of Valérie Jooste
Sent: woensdag 26 april 2006 17:04
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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