Does g variance change in adulthood? Testing the age de-differentiation hypothesis across sex

In the last decade, changes in the structure of intelligence across the life-span has become a central topic in the research on human intelligence. One of the main hypotheses that has arisen to account for such changes has been the age de-differentiation hypothesis [Balinsky, Genetic Psychology Monographs 23 1941, 191]. It predicts an increase in the importance of g, and a decrease in the number and importance of the lower-order abilities from early maturity to senescence. Despite of the research effort to test this hypothesis, no study has ever been conducted controlling by sex. For that purpose, males and females of the Spanish standardisation sample of the WAIS-III were analysed separately. Results show that the importance of g does not change with age irrespective of sex. Thus, the age de-differentiation hypothesis is rejected for both males and females. The indifferentiation hypothesis is supported as a more appropriate view of the changes in the structure of intelligence across adulthood.