Date: Wed, 3 Aug 2005 22:40:38 EDT
Reply-To: Marijaspss@aol.com
Sender: "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From: Marija Norusis <Marijaspss@aol.com>
Subject: Re: Reference Category for Categorical Vars in NOMREG
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On page 46 of the Advanced Statistical Procedures Companion it states,
"The SPSS Multinomial Logistic Regression procedure treats the last category
of a categorical or factor variable as the reference category and sets its
coefficient to 0. The variable male is coded 0 for no and 1 for yes, so males
are the reference category."
Marija Norusis
_www.norusis.com_ (http://www.norusis.com)
In a message dated 8/3/2005 5:30:22 P.M. Central Standard Time,
hmaletta@fibertel.com.ar writes:
By the way, in Marija Norusis' book (SPSS 13.0 Advanced Statistical
Procedures Companion) I find the explanation of this matter rather confusing
(p.47). First, it is not clear in her example which gender is 0 and which is
1: in the text it seems that the variable (confusingly called MALE) is zero
for males, since she says "For males the estimated value is just the
intercept, since the coefficient for the predictor variable is 0" whereas in
the accompanying table the category with B=0 is MALE=1. Secondly, the table
has a footnote regarding that zero, indicating that "The parameter is set to
zero because it is redundant", when in fact it is not exactly so: the true
explanation IMHO is that the parameter is zero by construction: the model
being tested establishes that the effect of being male is just the
intercept, and the effect of being female is the intercept plus the effect
of gender.
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