Seattle Longitudinal Study
a comprehensive ongoing study of intelligence and cognitive functioning from young adulthood to old age. Using a sequential design (a combination of cross-sectional and longitudinal data-collection methods), the study began in 1956, with testing done in 7-year intervals up to the present. Original testing was based on the Primary Mental Abilities Test (see primary ability); in subsequent intervals of the study, other tests were added to investigate various influences (e.g., cognitive style, personality, health, lifestyle, family environment, brain changes) on cognitive functioning during the aging process. Approximately 6,000 individuals, ranging in age from 22 to 103, have participated in the study since its inception. [conducted by U.S. psychologists K. Warner Schaie (1928– ) and, since 1983, Sherry L. Willis]