Ruminations on Aging Changes in Mental Abilities and Their Heritability: Comment on Finkel, Pedersen, Plomin, and McClearn (1998)

The Swedish Adoption/Twin Study of Aging is a semilongitudinal study of the aging of mental abilities in monozygotic and dizygotic twins. In the article by D. Finkel, N. L. Pedersen, R. Plomin, and G. E. McClearn (1998) , data from 602 individuals were used to investigate developmental changes on 14 measures of mental ability as well as changes in the heritability of these abilities. This commentary details a number of problems with the design and analysis of data reported by Finkel et al., problems that leave the results difficult to interpret, and then provides suggestions for more fruitful approaches for analyzing data from such studies in the future.