Evaluating the continuity of symptomatology between depressed and nondepressed individuals

Debate is contentious concerning whether depression should be viewed as a d istinct category or as a continuum including overlapping normal and clinica l phenomena. A nonparametric item response model was used to evaluate wheth er the probability of expressing individual symptoms differed between nonde pressed and clinically depressed adults experiencing similar levels of over all severity. Even though depressed and nondepressed individuals were equat ed in terms of overall severity, differences on specific symptoms emerged. Depressed mood, anhedonia, and suicidality were more likely to be expressed in depressed than in nondepressed individuals, whereas hypochondriasis and middle insomnia were more likely to be expressed in nondepressed individua ls at similar levels of severity. Such differences are inconsistent with th e view of depression as a simple continuum.