Reynolds & Keith. A test of Spearman’s law of diminishing returns in the Kauffman Assessment Battery for Children, Second Edition.
From Program Abstract
- According to Spearman’s “law of diminishing returns,” positive correlations among cognitive ability tests are higher in low ability groups versus high ability groups. Raw data from the Kaufman Assessment Battery for Children, Second Edition standardization sample were studied to determine if the phenomenon is present in this intelligence battery. The sample used in this study included 2175 participants ranging from 7 to 18 years in age. The sample was split into two groups: One group included individuals who had a Fluid-Crystallized Index (FCI) of 100 or below (low IQ group) and a second group included those who had a FCI of above 100 (high IQ group). The FCI is comparable to a Full Scale IQ score.
- Principal component analyses were used to replicate a previous study of the Wechsler Intelligence Scale for Children, Revised (Jensen, 2003). Confirmatory factor analyses using nested factor models were used to answer questions related to the changes in factor variances, subtest loadings on the g factor, and intercorrelations among broad ability factors. Results from the PCAs indicated that the law of diminishing returns was present in the KABC-II, although it was not produced uniformly across the subtests. Results from the CFAs indicated that higher g is associated with lower g variance, a depression of subtests’ g loadings, and lower intercorrelations between the broad ability factors. The law of diminishing returns was present in the KABC-II: g appears less general and more differentiated in a high IQ group compared to a low IQ group. This phenomenon was not produced uniformly across subtests, but it was also not produced only by the subtests with the weakest g loadings.