[R-sig-ME] General question about GLMM and heterogeneity of variance

[RH Gibson]

GibsonR <rachel.gibson <at> bristol.ac.uk> writes:

>
> My data have heterogeneity of variance (in a categorical variable), do I
need
> to specify a variance structure accounting for this in my model or do GLMMs
> by their nature account for such heterogeneity (as a result of using
> deviances rather than variances)? And if I do need to do this, how do I do
> it (e.g. using something like the VarIdent function in nlme) and in what
> package?


Added 29.02.2012


Sorry, I was not particularly clear.

 I ran my data through a GLM (the response variable is a proportion, and I
ignored the random effects for the purposes of data exploration), and
plotted the residuals against each of my predictor variables (some of
which are continuous, some categorical). The heterogeneity showed up in
the residuals of the response variable plotted against a categorical
predictor variable (Insect functional group).

Do I need to use something other than the GLMM in this case?

Thank you very much for your help.

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