On the inverse of covariance matrices for unbalanced crossed designs
非平衡交叉设计中协方差矩阵的逆
SUMMARY This paper addresses a long-standing open problem in crossed random-effects models under unbalanced designs: how to find an analytic expression for the inverse of $ {V} $, the covariance matrix of the observed response. For unbalanced crossed designs, $ {V} $ is dense, and the lack of a closed-form representation for $ {V}^{-1} $ has, until now, made the use of likelihood-based methods computationally challenging and difficult to analyse mathematically. We use the…