Final answer:
Cross-sectional studies of intelligence may reveal differences between young and old people that are influenced by characteristics of different cohorts, such as ethnicity and socioeconomic status.
Step-by-step explanation:
A cross-sectional study of intelligence may reveal differences between young and old people that do not arise from age, but from characteristics of different cohorts. These characteristics may include social and cultural experiences that differ between generations. For example, ethnic and socioeconomic factors can influence IQ test results, demonstrating that the differences in intelligence may not be solely attributed to age but rather to the cohort's background and experiences.