The depressive disorders are almost certainly etiologically heterogeneous, reflecting the convergence of multiple developmental pathways. Hence, it is likely that the role of personality factors and, as suggested above, the applicability of different models of the relation between personality and depression differ for different forms of depression. The current classification system for depressive disorders is based on clinical features and is a poor approximation of etiological distinctions. Nonetheless, it is important to consider whether the role of personality varies as a function of the specific depressive diagnosis (e.g., major depressive disorder, dysthymic disorder), subtype (e.g., psychotic, melancholic, atypical), and clinical characteristics such as age of onset, recurrence, and chronicity. Failure to take heterogeneity into account may obscure important personality-depression associations. Conversely, personality may provide a basis for identifying more homogeneous subgroups within the depressive disorders. Unfortunately, few studies of personality and depressive disorders have attempted to take this heterogeneity into account.
