The continuity of depression in clinical and nonclinical samples.

Historically, depression researchers have examined continuity in terms of whether the symptoms and characteristics of mild, moderate, and severe depression differ in degree along a continuum (i.e., a quantitative difference) or in kind (i.e., qualitative difference). The authors propose a differentiated framework that distinguishes 4 direct tests of continuity (i.e., phenomenological, typological, etiological, and psychometric continuity). They use this framework to suggest that most evidence is consistent with the continuity hypothesis. Moreover, they maintain that the findings of future research can be incorporated into a 2-factor model of depression that allows for both continuities and discontinuities.