The processes underlying these predictive associations are not entirely clear. One hypothesis is that personality change mediates the effect of treatment on depression. Indeed, there is a fair amount of evidence that depression treatment reduces N/NE and increases E/PE (Zinbarg et al. 2008) and that this effect is not due to confounding by the depressive state (Tang et al. 2009). Quilty et al. (2008b) tested a mediation model and found direct support for this hypothesis. Other possibilities need to be ruled out, however, particularly the hypotheses that traits predict poorer response because they indicate a more severe form of depression or that they interfere with treatment compliance and the therapeutic relationship, thus reducing the efficacy of the intervention.
