Structure, stability, and mean-level change in adolescent HEXACO personality traits using the HEXACO-SPI

• We used longitudinal data to explore the structure and stability of adolescent personality. • HEXACO-SPI scores were validated and reliable across adolescence. • Honesty-Humility, Extraversion, Agreeableness, and Conscientiousness decreased with age. • There were no changes to average levels of Emotionality and Openness to Experience. We used a new English version of the HEXACO-Simplified Personality Inventory (HEXACO-SPI) to examine (1) its dimensional structure and (2) the developmental stability and mean-level changes in its personality traits among adolescents. Our results showed that the HEXACO-SPI factor scales were consistent with the a priori hypothesized six-factor structure of HEXACO personality and that the HEXACO-SPI domain scales demonstrated sufficiently high levels of internal reliability, differentiation, and invariance across time. Stability was shown for all domain scales, but especially when considering 1-year estimates (versus 3 or 4-year estimates). Mean-level decreases were observed in Honesty-Humility, Extraversion, Agreeableness, and Conscientiousness, with stability in Emotionality and Openness to Experience. Our findings inform research on HEXACO personality in adolescence, including stability and change.