Spearman's Law of Diminishing Returns in Normative Samples for the WISC-IV and WAIS-III

Abstract

In order to explain observed variations in intelligence test scores, Spearman (1927 ) proposed the “law of diminishing returns” (SLODR). It states that the g saturation of cognitive ability tests decreases as a function of ability or age. Published studies have shown mixed results. However, a recent review ( Hartmann & Nyborg, 2004 ) suggests that there is evidence for differences in g saturation by ability level, but that observed age effects on g saturation are most likely to be a consequence of the ability effect. The current study analyzed the standardization data of the most recent Wechsler scales for both children and adults from several different countries. This study did not find evidence to support either the ability or age version of SLODR by using large normative samples for the WISC-IV from the United States, Canada, and Australia, and for the WAIS-III from the same three countries and also from The Netherlands.