Dispersion in cognitive functioning: Age differences over the lifespan.

INTRODUCTION A growing body of research suggests that intraindividual variability (IIV) may bring specific information on cognitive functioning, additional to that provided by the mean. The present paper focuses on dispersion, that is IIV across tasks, and its developmental trend across the lifespan. METHOD A total of 557 participants (9-89 years) were administered a battery of response time (RT) tasks and of working memory (WM) tasks. Dispersion was analyzed separately for the two types of tasks. RESULTS Dispersion across RT tasks showed a U-shaped age differences trend, young adults being less variable than both children and older adults. Dispersion across WM tasks (using accuracy scores) presented an opposite developmental trend. A cluster analysis revealed a group of individuals showing relatively little dispersion and good overall performance (faster in RTs and better in WM), contrasted with a group of individuals showing a large dispersion in the RT tasks as well as poorer overall performance. All young adults were grouped in the first cluster; children and older adults were distributed in both clusters. CONCLUSION It is concluded that (a) across-task IIV is relatively large in the entire sample and should not be neglected, (b) children and older adults show a larger dispersion than young adults, but only as far as the RT tasks are concerned,