Psychological characteristics of chronic depression: a longitudinal cohort study.

BACKGROUND Few studies have investigated the importance of psychological characteristics for chronicity of depression. Knowledge about psychological differences between chronically depressed persons and nonchronically depressed persons may help to improve treatment of chronic depression. This is the first study to simultaneously compare in large samples various psychological characteristics between chronically depressed and nonchronically depressed adults. METHOD Baseline data were drawn from the Netherlands Study of Depression and Anxiety (NESDA), an ongoing longitudinal cohort study aimed at examining the long-term course of depressive and anxiety disorders in different health care settings and phases of illness. Participants were aged 18 to 65 years at the baseline assessment in 2004-2007 and had a current diagnosis of DSM-IV major depressive disorder (N = 1,002). Chronicity of depression was defined as being depressed for 24 months or more in the past 4 to 5 years. The chronicity criterion was fulfilled by 31% (n = 312). The NEO Five-Factor Inventory measured the 5 personality domains, the Leiden Index of Depression Sensitivity-Revised was used to measure cognitive reactivity (eg, hopelessness, rumination), and the Mastery Scale measured external locus of control. RESULTS Compared to the nonchronically depressed persons, the chronically depressed persons reported significantly higher levels of neuroticism (OR = 1.81; 95% CI, 1.55-2.12; P < .001), external locus of control (OR = 1.94; 95% CI, 1.66-2.28; P < .001), and the following dimensions of cognitive reactivity: hopelessness (OR = 1.64; 95% CI, 1.43-1.88; P < .001), aggression (OR = 1.29; 95% CI, 1.13-1.48; P < .001), risk aversion (OR = 1.43; 95% CI, 1.24-1.63; P < .001), and rumination (OR = 1.55; 95% CI, 1.34-1.78; P < .001). They had significantly lower levels of extraversion (OR = 0.57; 95% CI, 0.49-0.67; P < .001), agreeableness (OR = 0.85; 95% CI, 0.74-0.97; P = .02), and conscientiousness (OR = 0.77; 95% CI, 0.67-0.88; P < .001). When testing these variables multivariably, the odds of chronic depression were significantly increased among those with low extraversion (OR = 0.73; 95% CI, 0.61-0.88; P = .001), high rumination (OR = 1.24; 95% CI, 1.01-1.53; P = .04), and high external locus of control (OR = 1.48; 95% CI, 1.21-1.80; P < .001). Controlling for severity of depressive symptoms, age at onset, comorbidity with anxiety disorders, medical illnesses, and treatment status did not change these results. CONCLUSIONS Our findings suggest that extraversion, rumination, and external locus of control, but not neuroticism, are differentiating psychological characteristics for chronicity of depression. These findings provide suggestions for more specific interventions, focused on extraversion, rumination, and external locus of control, in the treatment of chronic depression.