R help - Aug 2009 - Multiple comparison on lme model with 2 fixed factors

Hi!
I'm a bit lost while performing multiple comparisons on a lme model of that
type:

lmeglu=lme(glucose~Ath*tim,random=~1|Vol,na.action=na.omit,data=data)
multc = glht(lmeglu, linfct = mcp(Ath = "Tukey", tim =
"Tukey"))

This works fine for identifying the effect of each factor. However, when I
look for their interactions, l only obtain error messages.
For example this leads to a syntax error...
multc2 <- glht(lmeglu, linfct = mcp(Ath:tim = "Tukey", tim =
"Tukey"))

I try to identify/locate differences in glucose concentration (glucose in
the model) between groups (Ath) at each time point (tim).

Thanks a lot for your help
Regards
Virgile

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Billeke wrote:
> 
> I'm a bit lost while performing multiple comparisons on a lme model of
> that type:
> 
> lmeglu=lme(glucose~Ath*tim,random=~1|Vol,na.action=na.omit,data=data)
> multc = glht(lmeglu, linfct = mcp(Ath = "Tukey", tim =
"Tukey"))
> 
> This works fine for identifying the effect of each factor. However, when I
> look for their interactions, l only obtain error messages.
> For example this leads to a syntax error...
> multc2 <- glht(lmeglu, linfct = mcp(Ath:tim = "Tukey", tim =
"Tukey"))
> 
> I try to identify/locate differences in glucose concentration (glucose in
> the model) between groups (Ath) at each time point (tim).
> 
> 
Following the documentation, glht should not work with lme at all, but I
know it does and I have used it several times without interactions. But I
remember that the author, Torsten Hothorn, mumbled something like "keeping
track with lme/lme4 variants is like baby-sitting fleas" when I contacted
him on the subject, so there might be reasons the lme variant is
undocumented.

If you could prepare a small, reproducible example (use random data) that
shows the effect and the detailed error message, it could help tracking the
problem down.

Dieter



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