The utility of neuroticism in predicting first episodes of major depression was evaluated in a longitudinal study of 1,733 twins from female-female pairs and 1,862 twins from male-male pairs (Fanous, Neale, Aggen, & Kendler, 2007; Kendler, Neale, Kessler, Heath, & Eaves, 1993). Excluding participants who had already experienced an episode of depression by the time neuroticism was measured, each 1 standard deviation (SD) unit difference in higher neuroticism scores was associated with a 90–100% increase in the odds of developing major depression for the first time during the next 12 months in women (Kendler et al., 1993) and an 85% increase in men (Fanous et al., 2007). The strongest prospective study of neuroticism and depression to date involved 20,692 adult members of same-sextwin pairs from the population-based Swedish Twin Registry. Participants completed a measure of neuroticism in 1972–73 and were interviewed25 years later to determine if they had experienced major depression. Excluding individuals with an episode of major depression before 1974, each 1 SD difference in higher neuroticism was associated with a 31% greater risk for a first episode of
