[R] lme and mixed effects

[Peter Dalgaard BSA]

Douglas Bates <bates at stat.wisc.edu> writes:

> Doug Davidson <dvdsn at printhost.beckman.uiuc.edu> writes:
> 
> > With lme, is there a way to specify multiple fixed factors under one
> > level of grouping?
> 
> I'm not sure I understand the question.  Can you tell us more about
> the model that you want to fit?
> 
> If you mean that you want a random interaction term then you might
> want to check the description in section 1.3 of Pinheiro and Bates
> (Springer, 2000) on different ways that interactions can be expressed
> in lme.

I read it as two crossed within-subject terms. lme() is not quite
built for that with its emphasis on nested random effects, but this
kind of stuff has worked for me before:

> lme((y~fact1*fact2,
+       random=list(subj=pdIdent(form=~fact1-1),
+                   subj=~1,
+                   fact2=~1),

(That implies a subj within subj grouping, but the algorithm treats
that just like subj.)


> > For example, for a single fixed factor, I use the following:
> > 
> > fm1.lme <- lme(fixed=resp ~ fact1, random=~1|subj/fact1, data=mydata) 
> > 
> > 
> > I would like to have multiple factors under subj, like the following
> > for a two-way design, but I get an error:
> > 
> > 
> > fm2.lme <- lme(fixed=resp ~ fact1*fact2, random=~1|subj/(fact1+fact2), data=mydata) 
> 
> -- 
> Douglas Bates                            bates at stat.wisc.edu
> Statistics Department                    608/262-2598
> University of Wisconsin - Madison        http://www.stat.wisc.edu/~bates/
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-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907
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