Spearman's law of diminishing returns in hierarchical models of intelligence for children and adolescents

Spearman's “law of diminishing returns” or SLODR refers to a decrease in g saturation as ability level increases. SLODR has been demonstrated in a number of intellectual batteries but several important aspects of the phenomenon are not yet well understood. We investigated the presence of SLODR in the Kaufman Assessment Battery for Children—Second Edition (KABC-II), a popular measure of intelligence for children. We used confirmatory factor analysis to investigate the invariance of two hierarchical factor structures across ability groups; the subtest variance explained by the ability factors across groups; and whether SLODR was produced only by subtests with low loadings on the general ability factor. We found that SLODR was present in the KABC-II, and its presence was not dependent on the hierarchical model of intelligence. Moreover, our findings suggest that SLODR acts on g and not on the broad abilities, although the contribution of g to various broad abilities is lower in the high ability group. Finally, SLODR was not produced by the subtests with the lowest g loadings on the general factor.