A secular decline in Spearmanʹs g: evidence from the WAIS, WAIS-R and WAIS-III

Spearmanʹs law of diminishing returns posits that general intelligence, or simply g, exerts a lesser influence in high-IQ groups than in low-IQ groups. The present study examined this phenomenon across populations and time, using the standardizations of the WAIS, WAIS-R and WAIS-III. Average intercorrelations were compared across each of the standardization samples. Results indicate that a significant decline in the statistical power of Spearmanʹs g has occurred on a secular level, over a 46-year period. The largest decline seems to have occurred between 1955 (date of publication of the WAIS) and 1981 (date of publication for the WAIS-R). Maximum likelihood analysis confirmed the initial findings. Possible explanations for the differentiation of cognitive abilities are offered.