?interaction.plot Should help you. This works on the data, not the model. A 3-way interaction just means that the 2-way interaction differs among the various levels of the 3rd factor. Clever use of trellis plots (?xyplot -- especially ?panel.linejoin -- gives greater flexibility, but it requires that a steeper learning curve be climbed).
In general, the presence of interactions is just another manifestation of the response varying nonlinearly in the factors (**not** in the parameters, of course -- it's a linear model after all). This is essentially always the case, it's just a question of whether the signal/noise ratio (which depends on sample size) is large enough to see it via P-values. So by all means look at the plots and try to understand and interpret what's going on; but by no means assume that p-values above and below a threshhold of .05 are a clear guide to determining this. As usual, statistical significance and scientific relevance are not equivalent, and the degree of overlap between the two is often difficult to judge. Cheers, Bert Gunter Genentech Nonclinical Statistics South San Francisco, CA 94404 650-467-7374 -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Andrew Robinson Sent: Thursday, February 22, 2007 2:32 PM To: R. Baker Cc: [email protected] Subject: Re: [R] investigating interactions with mixed models Hello Rachel, I don't think that there is any infrastructure for these procedures on lmer objects, yet. If you are willing to use lme instead, then the multcomp package seems to provide post-hoc tests. It is worth noting that there is some doubt as to the validity of the reference distributions for tests of fixed effects in the presence of random effects. http://cran.r-project.org/doc/FAQ/R-FAQ.html#Why-are-p_002dvalues-not-displa yed-when-using-lmer_0028_0029_003f Cheers Andrew On Thu, Feb 22, 2007 at 12:32:44PM +0000, R. Baker wrote: > I'm investigating a number of dependent variables using mixed models, e.g. > > data.lmer45 = lmer(ampStopB ~ (type + stress + MorD)^3 + (1|speaker) + > (1|word), data=data) > > The p-values for some of the 2-way and 3-way interactions are significant > at a 0.05 level and I have been trying to find out how to understand the > exact nature of the interactions. Does anyone know if it is possible to run > post-hoc tests on mixed model (lmer) objects? I have read about TukeyHSD > but it seems that this can only be run on anova (aov) objects. > > Any suggestions would be gratefully appreciated! > > Rachel Baker > > -- > -------------------------------------------------------------------------- > PhD student > Dept of Linguistics > Sidgwick Avenue > University of Cambridge > Cambridge > > ______________________________________________ > [email protected] mailing list > 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. -- Andrew Robinson Department of Mathematics and Statistics Tel: +61-3-8344-9763 University of Melbourne, VIC 3010 Australia Fax: +61-3-8344-4599 http://www.ms.unimelb.edu.au/~andrewpr http://blogs.mbs.edu/fishing-in-the-bay/ ______________________________________________ [email protected] mailing list 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. ______________________________________________ [email protected] mailing list 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.
