Some support for our folk wisdom that happiness is a personal(ity) thing: Weiss et al. have used standard verbal and written questionnaires to examine personality and subjective well-being in 973 twin pairs. The written personality questionnaire used the five factor model (FFM) rating neuroticism, extraversion, openness to experience, agreeableness, and conscientiousness. Numerous studies of personality have shown that genetic effects account for approximately 50% of the variance in these FFM domains. The 'happiness' measure was by a telephone interview that asked three questions: how satisfied participants were with life at the present, how much control subjects felt they had over their lives, and how satisfied they were with life overall.
They found that the genetic structure of the FFM and subjective well-being could be modeled without genetic influences specific to subjective well-being. Subjective well-being was genetically indistinct from personality traits, especially those reflecting, in part, emotional stability (low neuroticism), social and physical activity (high extraversion), and constraint (high conscientiousness). The close genetic relationship between positive personality traits and happiness traits is the mirror image of comorbidity in psychopathology. Weiss et al. suggest that their findings indicate that subjective well-being is linked to personality by common genes and that personality may form an "affective reserve" relevant to set-point maintenance and changes in set point over time.