R help - Aug 2007 - Problem with lme using glht for multiple comparisons

Hi everyone,

I am new to R and have a question that relates to unplanned post-hoc comparisons
using the multcomp package after a mixed effects model. I couldn't find the
answer to it in the archive or in any manual.

I have a dataset in which several plants have been treated in a particular way
and a continuous response variable has been measured depending on several leaves
per plant. I am now interested in the effect of the treatment depending on the
age of the leaves examined. So the dataset (L1) consists of a continuous
response variable (EFN), a fixed factor (Leafage), and a random factor (Plant).

I have set up the following mixed effects model, which works fine:

> > LM<-lme(EFN~Leafage,L1,~1|Plant)
>   
Now all I want to do is a post-hoc analysis (multiple comparisons) for the fixed
factor EFN. I tried the following code. According to the documentation this
should work:

> > Post <- glht(LM, linfct = mcp(Leafage = "Tukey"))
>   
However, I get this error message and don't know what to do:

Error in mcp2matrix(model, linfct = linfct) : 
	Factor(s) Leafage have been specified in ?linfct? but cannot be found in
?model?!


The factor is specified, right? So what is the problem? If I do the same with an
normal Anova (command: aov), it works. What is the problem with the lme command?

Thank you very much in advance for your help.

Cheers,


Christian