The role played by E/PE in depression is less clear. Its cross-sectional association with dysthymia is substantial, but its relation to MDD is more modest. E/PE is not influenced by clinical state or changed by the experience of depressive episodes. It appears to be abnormally low even during remission, which is consistent with the continuation of trait deviance from the pre-morbid stage (precursor or predisposition accounts). Moreover, low E/PE tends to predict a poorer course of depression. However, the degree of shared etiological influences between E/PE and MDD is low, and the evidence that E/PE predicts the onset of MDD in prospective longitudinal studies is weak. As noted above, three possible reasons for the weaker and less consistent findings regarding E/PE are (a)it plays a greater role in some forms of depression than others (e.g., chronic depressions); (b) only some facets of the broader trait (e.g., low positive affective and approach motivation) are related to depression; and (c) E/PE may make a greater contribution to depression by moderating N/NE than as a main effect (Olino et al. 2010).
