Vulnerability to chronic depression: A review and preliminary model

Although depression has traditionally been conceptualized as an episodic, remitting condition, recent epidemiological studies of community samples and longitudinal studies of depressed patients indicate that a substantial number of individuals suffer from chronic forms of depression. For example, in the National Comorbidity Study, Kessler et al. [1] found that over 6% of a nationally representative community sample had experienced chronic depressions at some point in their lives. In the longitudinal follow-up component of the National Institute of Mental Health (NIMH) Collaborative Depression Study, over 19% of depressed patients experienced a chronic course with episodes lasting at least 2 years, and 7% still had not recovered after 8 years [2,3]. In light of this high prevalence, it is critical to elucidate the vulnerability factors that predispose to chronic depression and the processes that maintain depression after onset.