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st: marginal coding of dummy varaible

From   Valérie Jooste <>
To   <>
Subject   st: marginal coding of dummy varaible
Date   Wed, 26 Apr 2006 17:04:24 +0200

Dear all
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?
Thank you for your help

Valérie Jooste


	Valérie Jooste
	Registre des tumeurs digestives
	Recherche épidémiologique et clinique en cancérologie digestive
	Faculté de Médecine
	BP 87900
	21079 Dijon cedex
	Tel : 03 80 39 33 25
	Fax : 03 80 66 82 51

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