The basic goal of variance component estimation is to estimate the population covariation between random factors and the dependent variable. Depending on the method used to estimate variance components, the population variances of the random factors can also be estimated, and significance tests can be performed to test whether the population covariation between the random factors and the dependent variable are nonzero.

Estimating the Variation of Random Factors

Estimating Components of Variation

Testing the Significance of Variance Components

"Singular Hessian Matrix at Point of Conversion in Maximum Likelihood Estimation."