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Re: st: distinguishing categorical from ordinal variables in xtmixed

From   Maarten buis <>
Subject   Re: st: distinguishing categorical from ordinal variables in xtmixed
Date   Thu, 24 Apr 2008 19:24:23 +0100 (BST)

--- Olga Lyashevska <> wrote:
> We are trying to use xtmixed as a mixed effect anova taking advantage
> of maximum likelihood estimation.
> In xtmixed Stata seems to interprete categorical (cardinal) fixed
> factors (such as colour) as ordinals. How do we get Stata to treat
> these as a simple categorical?
> e.g.
> xtmixed y colour || individual
> where y is dependent continuous variable, colour is
> {red,green,blue}(coded with an integer) and individual is a random
> factor (coded with an integer)
> produces output in terms of regression coefficients etc. implying
> that STATA interpreted the categoricals as ordinal variables. As
> though the order was important, but of course it is not for
> categorical.

Have a look at -help xi- or the more flexible -findit xi3-.

Hope this helps,

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

visiting address:
Buitenveldertselaan 3 (Metropolitan), room Z434

+31 20 5986715

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