Primary aging, secondary aging, and intelligence.

The distinction between primary aging, representing innate maturational processes, and secondary aging, representing the effects of environment and disease (Busse, 1969), was used to develop a model for the assessment of factors that are associated with age-related individual differences in intelligence. Intelligence was measured by performance on a number of tests that measure cognitive abilities known to decline with age. In a hierarchical multiple regression analysis, primary aging and education but not health explained a significant portion of the variance in fluid intelligence. Chronological age had a residual effect over and above that of primary and secondary aging, indicating that there was remaining age-associated variance unaccounted for in the proposed model. The results suggest that the model of primary and secondary aging is a valid means of operationalizing chronological age.