EXPERIMENTAL DESIGNS FOR ESTIMATION OF HYPERPARAMETERS IN HIERARCHICAL LINEAR MODELS ⋆ Qing Liu Department of Statistics, The Ohio State University Angela M. Dean * Department of Statistics, The Ohio State University Greg M. Allenby Department of Marketing, The Ohio State University Abstract Optimal design for the joint estimation of the mean and covariance matrix of the random effects in hierarchical linear models is discussed. A criterion is derived under a Bayesian formulation which requires the integration over the prior distribution of the covariance matrix of the random effects. A theoretical optimal design structure is obtained for the situation of independent and homoscedastic random effects. For both the situation of independent and heteroscedastic random effects and that of correlated random effects, optimal designs are obtained through computer search. It is shown that orthogonal designs, if they exist, are optimal when the random effects are believed to be independent. When the random effects are believed to be correlated, it is shown by example that nonorthogonal designs tend to be more efficient than orthogonal designs. In addition, design robustness is studied under various prior mean specifications of the random effects covariance matrix.