Re: [R] step method in glm()

From: Prof Brian Ripley <ripley_at_stats.ox.ac.uk>
Date: Thu 13 Jul 2006 - 23:04:15 EST

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On Thu, 13 Jul 2006, Birycki Konrad DomBank Warszawa wrote:

> Hello,
>
> I estimaded two logit models via glm(). A null model (called glm00) and
> "full" model with all accessible covariates and interactions between them
> (glm1).
>
> Then I tried to get even better model by step procedure. I tried the
> following code:
>
> > step(glm00, scope=formula(glm1), method="both")
>
> and another one:
>
> > step(glm00, scope=formula(glm1), method="forward")
>
> In both cases step procedure terminated after several steps with a warning:
>
> > Error in factor.scope(ffac, list(add = fadd, drop = fdrop)) :
> > upper scope does not include model
>
> What does the word "model" refer to? To glm00 (the null model)? To my
> knowledge and understanding, the initial null model should have been
> included in every step of the search.
>
> Am I wrong?
>
> Thanks for all comments :-)
>
> Konrad Birycki
>
>
> [[alternative HTML version deleted]]
>
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-- 
Brian D. Ripley,                  ripley@stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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Received on Fri Jul 14 00:21:23 2006

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