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Re: st: Prediction at the 'mean' of a categorical- xi3?


From   "JVerkuilen (Gmail)" <jvverkuilen@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Prediction at the 'mean' of a categorical- xi3?
Date   Wed, 13 Mar 2013 09:30:40 -0400

On Wed, Mar 13, 2013 at 9:12 AM,  <graupel75@gmail.com> wrote:
> Dear Statalisters-
>
> I am attempting to do predictions from a model which includes clinical
> isolates as a predictor; these are important for good model fit, but
> not useful in and of themselves. With a continuous you would likely
> just set the reference to the median/mean, and predict away. Any
> suggestions in how to code it so I get something similar (a population
> average value) for a categorical in the presence of other covariates?

Nothing in the math says you can't center dummy variables; I do it all
the time using the usual Stata commands to make the intercept a
meaningful number. Effects coding in some sense does this in the
classic ANOVA setup but won't in a general regression due to the lack
of orthogonality.
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