On nonnegative quadratic unbiased estimability of variance components
Under a quadratic subspace condition, \textit{F. Pukelsheim} [ibid. 9, 293- 299 (1981; Zbl 0486.62066)] has proved that for estimating linear combinations of variance components, either standard methods provide a nonnegative quadratic unbiased estimate or such an estimate does not exist. This result is proved, replacing the quadratic subspace condition by a weaker condition. This answers in the negative a question raised by \textit{F. Pukelsheim} [Math. Operationsforsch. Stat., Ser. Stat. 12, 271- 286 (1981; Zbl 0488.62051)].
estimating linear combinations of variance components
scientific article; zbMATH DE number 3883440