Birth cohort changes in extraversion: a cross-temporal meta-analysis, 1966–1993

This paper examines change over time in American college students’ scores on the extraversion scales of the Eysenck Personality Inventory and the Eysenck Personality Questionnaire. The meta-analysis aims to investigate birth cohort as a proxy for the larger sociocultural environment, a previously unexamined influence on personality beyond genetics and family environment. Data collection strategies yielded 59 studies reporting data on 16,846 students. Correlations between extraversion scores and year of data collection were positive and strong (≥0.65) for both men and women and across both measures, suggesting that extraversion has increased over time. The increase is large, between 0.79 and 0.97 standard deviations (SDs) over 20–25 years, explaining between 14 and 19% of the variance in personality over this time