Dear all,
I wonder if anyone can help me with specifying a right model for my
analysis. I am a beginner to lme methods. I was unfortunately not able to
find a solution to my problem on my own.
Data structure:
I have sampled monthly 6 basins during two hydrological cycles, and I have
taken several (2 to 4) samples (replicate) for each basin and month. Im
trying to relate Shannon diversity to some environmental variables, taking
away pseudoreplication. Thus, I have tried an lme model with time and
basin as random factors. I have put hydrological cycle as a fixed factor,
since Im interested in quantifying their effect. But Im not sure if there
are other possibilities to do this.
This is my model structure:
Model1<-lme(shannon<-log(chla+1)*hyd_cycle+toc*hyd_cycle,
random=~time|basin)
Note that I have not put replicate within the random structure
(random=~time|basin/replicate), and this is my major concern. Im not sure
if I have to include replicate in the random structure, since replicates
are randomly taken each time, and so are not repeated measures within the
basins.
All books and internet information that I have looked at the moment are
examples with repeated measures within blocks (e.g. repeated measures of the
same plant and treatment). Can anyone help me with this?
I would appreciate any hints and suggestions
Stéphanie
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