Empirical Investigation of Two Assumptions in the Diagnosis of DSM-IV Major Depressive Episode

Objective: The aim of the current study was to examine two major assumptions behind the DSM-IV diagnosis of major depressive episode (MDE): that depression represents a distinct category defined by a valid symptom threshold, and that each depressive symptom contributes equally to the diagnosis. Methods: Data were from the Australian National Survey of Mental Health and Wellbeing. Participants consisted of a random population-based sample of 10 641 community volunteers, representing a response rate of 78%. DSM-IV diagnoses of MDE and other mental disorders were obtained using the Composite International Diagnostic Interview, version 2.0. Analyses were carried out on the subsample of respondents who endorsed either depressed mood or loss of interest (n =2137). Multivariate linear regression analyses examined the relationship between the number and type of symptoms and four independent measures of impairment. Results: The relationship between the number of depressive symptoms and the four measures of impairment was purely linear. Three individual symptoms (sleep problems, energy loss, and psychomotor disturbance) were all independent predictors of three of the four measures of impairment. Conclusions: Counting symptoms alone is limited in guiding a clear diagnostic threshold. The differential impact of individual symptoms on impairment suggests that impairment levels may be more accurately estimated by weighting the particular symptoms endorsed.