Analysis of a multicenter trial using a multivariate approach to a mixed linear model
In a multicenter comparative trial with ttreatments, the centers are treated as a random sample from a t-variate normal population. The model studied in this paper deals with unbalanced data and accommodates one or more covariates. The maximum likelihood estimates of the parameters are derived without any constraints on Ω, the dispersion matrix of a random vector associated with a center. The likelihood ratio test for comparing the treatments is derived. The dispersion matrix of the maximum likelihood estimators is derived and a numerical example is given to illustrate the methodology.