When mental abilities are studied through cross-sectional methods, the results c

Longitudinal studies examine the same people over a period of time, reassessing them periodically.
Cross-sectional studies examine groups of people of different ages at the same time.
Longitudinal studies are especially useful to study changes in individuals over time.
Cross-sectional studies are more useful when studying generational differences.
When comparing the mental test scores of younger and older people, cross-sectional studies usually indicate that younger people achieve higher scores.
Longitudinal studies, in contrast, do not indicate any decline until people are in their 70s or 80s.