The most direct approach to testing the precursor and predisposition models is to conduct prospective studies of personality in never-depressed participants to determine whether personality characteristics predict the subsequent onset of depressive disorders. Several studies using large community samples have reported that higher levels of N/NE predict the onset of first lifetime MDD episodes (de Graaf et al. 2002; Fanous et al. 2007; Kendler et al. 1993, 2006; Ormel et al. 2004a). In addition, several studies using measures of other traits that overlap with N/NE or its facets have reported similar findings (Hirschfeld et al. 1989, Rorsman et al. 1993). Although there is some evidence that E/PE predicts the first onset of MDD (Kendler et al. 2006, Rorsman et al. 1993), it is much weaker, and several studies have failed to find an association (Fanous et al. 2007, Hirschfeld et al. 1989, Kendler et al. 1993).
