[R] interaction contrasts

[Kay Cichini]

hello,

i was shortly asking the list for help with some interaction contrasts (see
below) for which
i had to change the reference level of the model "on the fly" (i read a post
that this is possible in 
multcomp).

if someone has a clue how this is coded in multcomp; glht() - please point
me there.

yours,
kay


Kay Cichini wrote:
> 
> hello list,
> 
> i'd very much appreciate help with setting up the 
> contrast for a 2-factorial crossed design.
> 
> here is a toy example:
> 
> library(multcomp)
> 
> dat<-data.frame(fac1=gl(4,8,labels=LETTERS[1:4]),
>                 fac2=rep(c("I","II"),16),y=rnorm(32,1,1))
> 
> mod<-lm(y~fac1*fac2,data=dat)
> 
> ## the contrasts i'm interressted in:
> 
> c1<-rbind("fac2-effect in A"=c(0,1,0,0,0,0,0,0),
>           "fac2-effect in B"=c(0,1,0,0,0,1,0,0),
>           "fac2-effect in C"=c(0,1,0,0,0,0,1,0),
>           "fac2-effect in D"=c(0,1,0,0,0,0,0,1),
> 	    "fac2-effect, A*B"=c(0,0,0,0,0,1,0,0),
>           "fac2-effect, A*C"=c(0,0,0,0,0,0,1,0),
>           "fac2-effect, A*D"=c(0,0,0,0,0,0,0,1))
> 
> summary(glht(mod,c1))
> 
> ## now i want to add the remaining combinations 
> ## "fac2, B*C"
> ## "fac2, B*D"
> ## "fac2, C*D"
> ## to the simultanous tests to see whether the effects 
> ## of fac2 within the levels of fac1 differ between  
> ## each combination of the levels of fac1, or not ??
> 
> thanks for any advise!
> 
> yours,
> kay
> 
> 
> 


-----
------------------------
Kay Cichini
Postgraduate student
Institute of Botany
Univ. of Innsbruck
------------------------

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