Hi I am running some linear and non-linear mixed effect models and would like
to do some planned contrasts (a priori contrasts)
I have looked in the help and in many forums and it seems possible to do so but
don't understand how to write the function and I couldn't find an example in
Pinheiro and Bates.
lme {nlme} has a contrasts argument but I can't understand how to code it.
Here is a simple example of my working lme model:
dependent variable: APHIDS: log (number of aphids)
Fixed effects: DAY (time) and TREATMENT ( 6 different aphid treatments)
Random effects: POPULATION (each population is counted through time)
lme.fit<-lme(log(APHIDS)~ DAY*TREATMENT, random = ~ DAY|
POPULATION,data= aphid.data)
My hypothesis testing focuses on comparing Treatments ~ 1 and 4 , and
eventually 2 vs 5, and 3 vs 6.
Q1: How can I do planned contrasts on these pairs for the main effect of
TREATMENT?
Q2: Can I also do this for the interaction term (DAY*TREATMENT)?
Q3: Would this code work for a non-linear mixed effect model nlme( )
P.S. Even just posting a personal example or a link to one would be greatly
appreciated.
thanks for the help
these forums are incredibly helpful
Martin Turcotte
mart.turco...@gmail.com
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