[R] Multiple comparison on lme model with 2 fixed factors

[Billeke]

Sorry to come back again, but with this and other (real) data, I'm not able
to obtain those comparisons. I'm using the following command and obtain the
following result (lmer model).

glht(lmelac.ex, linfct = mcp("ath1:tim20 - ath1:tim40 = 0"="Tukey"))->comp
Erreur dans mcp2matrix(model, linfct = linfct) : 
  Variable(s) ‘ath1:tim20 - ath1:tim40 = 0’ have been specified in ‘linfct’
but cannot be found in ‘model’! 

After looking at the model obtained in nlme, the interactions are not
present. However, I'm not able to find any object in lmer objects

May I ask for your help again?
THanks a lot
Virgile



Dieter Menne wrote:
> 
> 
> 
> Billeke wrote:
>> 
>> 
>> mult2 <- glht(lmelac.ex, linfct = mcp("ath:time" = "Tukey"))
>> 
>> 
> 
> I don't have the time to check, but got a mail for Torsten (author) with
> the following idea:
> 
> glht(lmeglu, linfct = c("Ath1:tim2 - Ath1:tim3 = 0", ...))
> 
> He suggested to build the matrix explicitly instead; that's what I
> normally do, but I admit that I use an Excel spreadsheet to get the
> coefficients right in such a case.
> 
> Technically, using time as a categorical parameter is not recommended
> because of serial correlations. Try to fit a linear or linearized model
> instead to time, or, if you cannot do it otherwise, a nonlinear one.
> 
> I too often see my colleagues asking questions like "how many days after
> treatment start do I first see significant effects on my lymphocyte
> count"? This gives many p-values for a publication, and that's what
> medical reviewers love. Your approach to use multcomp to correct for this
> is a fair way out, but doing serious trend analysis is better.
> 
> Dieter
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 

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