Estimation of the multivariate normal covariance matrix under some restrictions
Abstract We consider the estimation of Σ of the p -dimensional normal distribution N p (0, Σ ) under the restriction where the eigenvalues of Σ have an upper or lower bound. From a decision-theoretic point of view, we evaluate the performance of the REML (restricted maximum likelihood estimator) with Stein′s loss function and propose another estimator that dominates the REML.