[R-sig-ME] MCMCglmm: ixn between binary family-level factor and us() random effect

[Paul Johnson]

I'm fitting models to estimate mother-father and parent-offspring covariances, using

   random = ~us(offpar.f):famid

where offpar.f is a factor with 3 levels: offspring, mother, father and "famid" is the family ID. This allows me to compare the strengths of mother-offspring and father-offspring correlations within familes. The next step is to compare these covariances between asthma families (AF) and non-asthma families (NAF). I.e. I want to estimate three covariances within each level of the NAF/AF factor while setting the covariances between NAF and AF families to zero. The structure of the 6x6 covariance matrix should be

   VAF   0
   0     VNAF

where VAF and VNAF are 3x3 US covariance matrices and the 0s are 3x3 blocks of zeros.
How can I specify this in a formula? I've tried various random formulae based on what I found in the MCMCglmm course notes and this list but with no success.

Thanks for any help,
Paul


The University of Glasgow, charity number SC004401