This paper sought to extend previous research findings linking personality abnormalities to chronicity (Duggan et al., 1990
; Hirschfeld et al., 1986a
) and age of onset (Fava et al., 1996
; Ramklint & Ekselilus, 2003
) by examining them in the same sample. The goals of this study were twofold: 1) to determine whether there were unique associations between chronicity and age of onset of depression and reports of personality traits at baseline, 2) to evaluate whether the associations between clinical characteristics and reports of personality traits would remain consistent over time.
The results suggested that people who reported higher levels of trait negative emotionality were more likely to have developed affective disturbance at an early age. Results also suggested that depressed people who reported lower levels of trait positive emotionality were more likely to have a chronic course. This pattern of findings was maintained regardless of whether personality was the predictor or the criterion, thus strengthening our argument for unique associations.
Furthermore, findings from the present study suggested that the associations between personality and age of onset and chronicity of depression were consistent across time, in that chronicity of depression retained its association with trait positive emotionality (albeit at a trend level) and early onset of depression retained its association with trait negative emotionality at 6-month follow-up. Together, these findings accentuated the unique associations between reports of personality traits and age of onset and chronicity of depression.
We found that age of onset and chronicity possessed unique associations with personality reports over and above depression state effects. It was essential to adjust our participants' reports for current depressive severity because even though depressives exhibit personality irregularities before, during, and after a depressive episode compared to controls (Ormel et al., 2004
), their reports of personality are affected by their depressive state (Reich et al., 1987
). Indeed, we found that over time, a change in depressive symptoms led to a medium change in personality ratings. Thus, our study argues for the importance of considering state effects on depressed individuals' ratings of their personality (Klein et al., 2002
; Rohde et al., 1990
Because our measures of depression and personality were assessed concurrently, we were unable to determine whether personality caused
the clinical characteristic or whether the clinical characteristic caused
the personality characteristic. Indeed, the relation between depression and personality is complex, with some studies showing that personality predicts later onset of depression and others showing that depression has `scar' effects on personality (Fanous et al., 2007
; Kendler et al., 1993
; see Klein et al., 2002
). Thus, it was important in the present study to examine personality as both the predictor and the criterion. It is interesting, however, that in both sets of analyses, the pattern of unique associations was maintained.
Given that elevated levels of negative emotions both uniquely predict and are uniquely predicted by an early age of onset of depression, negative emotionality/neuroticism may play an etiological role in depression occurring early in life. Research has established links between stressful life events and onset of depression (Kendler et al., 1995
; Kessler, 1997
), and studies have found that people with higher levels of stress reactivity or tendency to experience negative emotions are more vulnerable to stress (van Os & Jones, 1999
) and more prone to develop depression when stressful events occur (Kendler et al., 2006
). Thus, our results may suggest that a person with high trait negative emotionality may have a predisposed lower threshold (or higher sensitivity) to the depressogenic effects of stress.
Our study also found that low levels of positive emotions both predict and are predicted by a chronic course of depression. That is, an individual who has low positive emotionality may be less likely to engage in pleasurable experiences than someone who reports a normal level of this trait (Gable et al., 2000
). With this in mind, it is possible that a depressed individual with low levels of positive emotions may neglect to seek social experiences or interpersonal contact, which may in turn contribute to the maintenance (and thus, the chronicity) of their depressive symptoms. Cognitive-behavioral therapeutic techniques for depression that focus on behavioral activation may thus be particularly important to use with these individuals as behavioral activation seeks to increase a patient's social activities and interpersonal communication and thus increase the likelihood that they would experience positive emotions (Dimidjian et al., 2006
; Jacobson et al., 2001
The notion that reports of elevated negative emotionality and lowered positive emotionality are relatively consistent over time among individuals who experience depression is not new (Cox et al., 2004
; Hirschfeld et al., 1986b
; Ormel et al, 2004
), nor is the examination of the roles of onset age and chronicity (McCullough et al., 2003
; Parker et al., 2003
; Ramklint & Ekselius, 2003
). However, our finding of unique, consistent associations between particular clinical characteristics and particular personality traits is an important contribution to the literature on depression and personality and increases the validity of the distinction between early onset and chronic depressions. Researchers tend to equate early onset of depression with chronicity of depression, suggesting that both are persistent and pernicious subtypes of the disorder (Waslick et al., 2003
). However, this study suggests that there are different emotional processes associated with these clinical characteristics. It is, of course, necessary to replicate these findings with a larger sample.
The present study had several limitations. First, self-report personality inventories may not adequately assess underlying personality features of individuals. Depressed individuals may feel motivated to make their responses correspond to the way they think they should describe their feelings according to their present diagnoses (i.e., demand characteristics). Second, the current study focused exclusively on measuring personality traits, as opposed to using idiographic personality assessments (Cervone, 2004
). Third, our cross-sectional data collection methodology did not allow us to draw causal conclusions regarding personality and depression. Fourth, reliabilities on depressive diagnoses, ages of onset, and chronicity were not obtained; however, the lab has obtained adequate reliabilities in the past, and all diagnosticians went through extensive training (Klein et al., 2000
). Lastly, due to our small sample size, we had only moderate statistical power (69%) to test our hypotheses and inadequate statistical power to detect interactions between age of onset and chronicity of depression, a combination that we expect to present an increasingly negative personality profile.
However, the present study also had several strengths. First, by examining the unique personality factors associated with early onset and chronicity of depression, we were able to identify early vulnerability factors for onset and maintenance of a depression episode. Second, the longitudinal design enabled us to examine the stability of personality and depression over time. Third, we used multiple personality assessment measures (GTS, EPQ, and BIS/BAS scales) of similar constructs, which enabled us to obtain more valid measures of positive and negative emotionality.