Hello all,

I am using MCMCglmm and attempting to create a model which allows
heterogeneous variances for different levels of a moderator variable where
the moderator is an interaction term. I attempted the run the following
model:

prior=list(R=list(V=diag(12),n=0.002),G=list(G1=list(V=diag(12),n=0.002),G2=list(V=diag(12),n=0.002)))

model=MCMCglmm(grad.lin~pop.bin*group,mev=mev,data=data,prior=prior,random=~idh(pop.bin*group):study
+idh(pop.bin*group):pop,rcov=~idh(pop.bin*group):units,nitt=300000,burnin=100000,thin=50)

where "pop.bin" corresponds to bins of population size and has 4 levels,
and "group" has 3 levels (Fish, Birds, Plants).

When I run the above model I receive the error:
Error in priorformat(if (NOpriorG) { :V is the wrong dimension for some
prior$G/prior$R elements4

I tried running a simpler model with just "pop.bin" instead of the
interaction term and "V=diag(4)" in the prior, and it seems to run just
fine.

I'm unsure whether the problem is simply too many levels and I perhaps
don't have enough data or statistical power to run this model or whether I
made a simple (or huge) error in the model or prior specification. If
anyone could shed some light on this it would be a huge help.

Cheers,
Jackie


-- 
Jacquelyn L.A. Wood, MSc.
PhD Candidate
Biology Dept.
Concordia University
7141 Sherbrooke St. West
Montreal, QC
H4B 1R6
Phone: (514) 293-7255
Fax: (514) 848-2881

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