An analysis of diversity in the cognitive performance of elderly community dwellers: individual differences in change scores as a function of age.

This longitudinal study investigated whether age is associated with increases in interindividual variability across 4 ability domains using a sample of 426 elderly community dwellers followed over 3.5 years. Interindividual variability in change scores increased with age for memory, spatial functioning, and speed but not for crystallized intelligence for the full sample and in a subsample that excluded dementia or probable dementia cases. Hierarchical regression analyses indicated that being female, having weaker muscle strength, and having greater symptoms of illness and greater depression were associated with overall greater variability in cognitive scores. Having a higher level of education was associated with reduced variability. These findings are consistent with the view that there is a greater range of responses at older ages, that certain domains of intelligence are less susceptible to variation than others and that variables other than age affect cognitive performance in later life.