[R] need help with an interaction term
ccatj at web.de
Thu Aug 31 22:15:04 CEST 2006
many thanks for your advice.
IŽll go through the package and see if IŽll 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.
but could not yield any plausible results. Hopefully this time...
> -----Ursprüngliche Nachricht-----
> Von: Chuck Cleland <ccleland at optonline.net>
> Gesendet: 31.08.06 14:16:12
> An: Christian Jones <ccatj at web.de>
> CC: r-help at stat.math.ethz.ch
> Betreff: Re: [R] need help with an interaction term
> Christian Jones wrote:
> > Hello!
> > Iï¿œm 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:
> > Christian
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> Chuck Cleland, Ph.D.
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