Patterned Variance-Covariance matrices for the random effect
On Tue, Aug 4, 2009 at 2:22 PM, Tahira Jamil<tahirajamil at yahoo.com> wrote:
Hi everyone
I am wondering How can I assign special patteren / form e.g. compound symmetry structure , block diagonal etc to variance-covariace matrices to mer calss.
As in nlme library we have pdMat classes to specify patterened variance-covariance matrices for the random effects. Hope to have some help from group members.
The functions in the lme4 package do not allow for arbitrary specification of the variance-covariance matrix for the random effects. Generally you specify random effects terms in the model formula and the variance-covariance matrix of the random effects is derived from the rules random effects have a multivariate Gaussian distribution with mean zero random effects associated with different terms in the formula are independent random effects associated with different levels of the grouping factor in a given term are independent random effects associated with the same level of the grouping factor in a given term have a general positive semidefinite variance-covariance structure that is common to all levels.