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List:       r-help
Subject:    Re: [R] need help with an interaction term
From:       Christian Jones <ccatj () web ! de>
Date:       2006-08-31 20:15:04
Message-ID: 702716241 () web ! de
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Hello Chuck,
many thanks for your advice.
I´ll go through the package and see if I´ll manage to visualize the interaction \
effect this time as I already tried it with a special tool for displaying models with \
interaction terms in 3D.  \
http://www.uni-oldenburg.de/landeco/Download/Software/LR_Mesh/LR_Mesh.htm but could \
not yield any plausible results. Hopefully this time... best regards
Christian

> -----Ursprüngliche Nachricht-----
> Von: Chuck Cleland <ccleland@optonline.net>
> Gesendet: 31.08.06 14:16:12
> An: Christian Jones <ccatj@web.de>
> CC: r-help@stat.math.ethz.ch
> Betreff: Re: [R] need help with an interaction term


> Christian Jones wrote:
> > Hello!
> > I�m fitting a model with glm(family binomial). The best model counts 9 \
> > Variables and includes an interaction term that was generated by the product of \
> > to continuous variables (a*b). All variables are correlated under a value of 0.7 \
> > (Spearman rank order) While the estimates of both main effects are negativ, the \
> > resulting interaction term is positiv. This change of sign makes it difficult to \
> > interpret the model and above all, is this perhaps due to a bad variable choice ? \
> > Thanks a lot for helping
> 
> Rather than trying to interpret the model coefficients directly, you
> might visualize the a*b interaction effect.  The effects package by John
> Fox is very useful for this:
> 
> http://cran.r-project.org/doc/packages/effects.pdf
> 
> > Christian
> > 
> > _______________________________________________________________________
> > Viren-Scan für Ihren PC! Jetzt für jeden. Sofort, online und kostenlos.
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> > 
> > ______________________________________________
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> > https://stat.ethz.ch/mailman/listinfo/r-help
> > PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> > and provide commented, minimal, self-contained, reproducible code.
> 
> -- 
> Chuck Cleland, Ph.D.
> NDRI, Inc.
> 71 West 23rd Street, 8th floor
> New York, NY 10010
> tel: (212) 845-4495 (Tu, Th)
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> 

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