Random-effects variance-covariance matrix in lmer?
Hi all I'm looking for a way to specify a more complex variance-covariance matrix for the random effects in lmer(). For example, in lme() (nlme package), there are the pdMat classes to specify e.g. a compound symmetry (pdCompSym) or a multiple of an identity (pdIdent) structure for the variance-covariance matrix of random effects. Is there a possibility to code an equivalent for lmer()? I'm specifically interested in "compound symmetry" and "multiple of an identity". I assume that Douglas Bates or Ben Bolker have a distinct answer on that. Thanks in advance, Matthias --------------------------------------------------------- Matthias Suter, Dr.sc.nat. Forage Production and Grassland Systems Agroscope Reckenholzstrasse 191, CH-8046 Z?rich Phone +41 58 468 75 90 Fax +41 58 468 72 01 matthias.suter at agroscope.admin.ch www.agroscope.ch ---------------------------------------------------------