ON EXACT D-OPTIMAL DESIGNS FOR REGRESSION-MODELS WITH CORRELATED OBSERVATIONS

Let tau* be an exact D-optimal design for a given regression model Y(tau) = X(tau)beta + Z(tau). In this paper sufficient conditions are given for designing how the covariance matrix of Z(tau) may be changed so that not only tau* remains D-optimal but also that the best linear unbiased estimator (BLUE) of beta stays fixed for the design-tau*, although the covariance matrix of Z(tau)* is changed. Hence under these conditions a best, according to D-optimality, BLUE of beta is known for the model with the changed covariance matrix. The results may also be considered as determination of exact D-optimal designs for regression models with special correlated observations where the covariance matrices are not fully known. Various examples are given, especially for regression with intercept term, polynomial regression, and straight-line regression. A real example in electrocardiography is treated shortly.