Dear all,
I am studying the possibility of using the nlme package in R to analyse field trials of agricultural crops. I have a problem with the syntax for the modelling of variance covariance structures. I can model the within-group covariance structure using the correlation argument and the covariance structure between different random effects of the same grouping level using 'random=pdDiag(~effect)|group' but I would like to model the covariance structure' between' the different levels of the grouping factor. This is necessary because the plants (= grouping factor) we are testing are not independant. They are genetically correlated and usually we know this correlation. I would therefore also like to specify the exact (not starting) values of this 'between subjects correlation'.
Can you tell me if this is possible in R and how the syntax of such a model would look like?
thank you in advance,
P.
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