[R] investigating interactions with mixed models

[Andrew Robinson]

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-displayed-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
> 
> -- 
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-- 
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
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