The aim of this study was to investigate the relationships among morningness-eveningness, impulsivity and anger in the general population. A total of 1000 community-dwelling subjects (500 males) aged 20-77 years (mean± SD age: 39.6 ± 11.6 years) completed the morningness-eveningness questionnaire (MEQ), Barratt impulsiveness scale (BIS), Spielberger State-Trait Anger Expression Inventory (STAXI) and Center for Epidemiologic Studies Depression Scale. Moderation and mediation analyses were performed to determine whether the relationship between two variables depended on the third variable, referred to as a moderator, and whether the third variable, known as a mediator, was associated with the other two variables establishing causation. The MEQ scores exhibited significant negative associations with BIS (p < 0.001) and STAXI (p < 0.001) scores, and high scores on the BIS were associated with high scores on the STAXI (p < 0.001). Impulsivity, as measured by the BIS, played a role as a moderator (p < 0.001) in the relationship between MEQ and STAXI, and anger, as measured by the STAXI, acted as moderator (p = 0.030) in the association between MEQ and BIS. However, after controlling for the interaction of the BIS and MEQ, the MEQ scores did not significantly predict STAXI scores (p = 0.070). Additionally, the effect size of the mediating effect of the BIS scores on the relationship between the MEQ and STAXI (percent mediation: 53.2%) was larger than that of the STAXI scores on the association between the MEQ and BIS (percent mediation: 31.8%). The present results demonstrate that morningness-eveningness was closely related with both impulsivity and anger in the general population. Furthermore, these findings suggest that impulsivity may exercise a great influence on the association between morningness-eveningness and anger in two ways: as a moderator by modulating this relationship based on the level of impulsivity and as a mediator by acting as an intermediary factor.
