Measuring relative importance of sources of variation without using variance

This article proposes a new parameter, the group or class dominance probability, to measure the relative importance of random effects in one-way random effects models. This parameter is the probability the group random effect is larger in absolute size than the individual (or error) random effect. The new parameter compares the middle part of the distributions of the two sources of variation, and pays little attention to the tails of the distributions. This is in contrast to the traditional approach of comparing the variances of the random effects, which can be heavily influenced by the tails of the distributions. We suggest parametric and nonparametric estimators of the group dominance probability, and demonstrate the applicability of the ideas using data on blood pressure measurements.