Date:         Wed, 29 Oct 2003 08:49:06 +0000
Reply-To:     Muir Houston <hous-ca0@wpmail.paisley.ac.uk>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         Muir Houston <hous-ca0@wpmail.paisley.ac.uk>
Subject:      Re: qu. about choosing reference groups
Comments: To: jwegbrei@HSPH.HARVARD.EDU
Content-Type: text/plain; charset="us-ascii"

If you want to choose category 2 then you need to construct 3 'dummy'
variables and then put the dummy variables for catefgories 1 & 3 into
model 2 is then reference
this can be done with all catgorical variables to allow specific
selection of reference group

as to the last point - in the specification did it say it had included
all variables in the model?
what enter method are you using? bacward stepwise, forward stepwise,
wald, maximumlikelihood?

muir houston


>>> jwegbrei <jwegbrei@HSPH.HARVARD.EDU> 10/27/03 10:42pm >>>
i'm doing logistic regression and have categorical predictor variables.
i'm
having difficulty choosing reference groups for those predictor
variables.
when defining my variables as categorical i have  chosen a simple
contrast. if
i chose the 'first' reference category, will it use the category coded
as '1'
(if 1,2,3, categories) as the reference group? and if i chose 'last'
will it
then use '3' as the reference category.  and what should i do if i want
to use
'2' as my reference category? is there any way of specifying a
reference
category besides the first or last?
last, what should i do if after choosing chosing a simple contrast and
using
the first reference category and then running my regression, the
various
categories don't appear in the output and only the variable name
appears?



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