In this note we extend the Gauss-Markov theorem to the case of singular covariances and give an explicit formula for the BLUE of an estimable parameter. The formula reduces to the usual one when the ...

Hilmar Drygas, Sufficiency and Completeness in the General Gauss-Markov Model, Sankhyā: The Indian Journal of Statistics, Series A (1961-2002), Vol. 45, No. 1 (Feb., 1983), pp. 88-98 ...