Prevalence and clinical course of depression: A review
Highlights
► Epidemiological studies demonstrate that depressive disorders are highly prevalent. ► Recovery rates have begun to demonstrate the complexity of the nature and course of depression. ► Relapse and recurrence are key in understanding depression, as they carry the threat of chronicity. ► A key variable influencing recovery is the presence of comorbid illnesses, medical or psychiatric. ► The global cost of depression far outweighs the cost to treating successfully those who suffer.
Introduction
Depression is one of the most commonly diagnosed mental disorders among adults. Our understanding of the course and nature of depression has changed significantly in the last 20 years. From being seen as an acute and self-limiting illness, to a growing clarity that for many depression is now considered a chronic, lifelong illness. Prevalence of depression is of concern, as the cost that depression exacts is considerable. It is not only economically detrimental, but also engenders significant personal and interpersonal suffering alongside its societal impact (Johnson, Weissman, & Klerman, 1992). This review considers the literature on Major Depression beginning with a brief historical overview, its classification, and a synthesis of the current knowledge regarding prevalence and course.
Section snippets
Historical development
Historically, mood disorders have been conceived as either “organic” or “reactive,” as found in the Diagnostic and Statistical Manual of Mental Disorders—First Edition (DSM-I) (American Psychiatric Association [APA], 1952). The second edition of the manual (DSM-II) (American Psychiatric Association [APA], 1968) continues this basic distinction using the terms “psychotic” and “neurotic.” Mood disorders were understood as either a disease of the brain and organic, or neurotic and therefore a
Classification
The Diagnostic and Statistical Manual of Mental Disorders—Fourth Edition (DSM-IV-TR) (American Psychiatric Association [APA], 2000) describes a Major Depressive Disorder (MDD) diagnosis based on the presence of a specified number of symptoms with a precise duration. Primarily symptoms of either depressed mood or loss of interest or pleasure are present. Additionally the criteria of at least five items from the DSM-IV-TR (APA, 2000) list need to be present for a duration of 2 weeks and as such,
Epidemiology of depression
Several major epidemiological studies have been carried out to determine the prevalence of depressive disorder in the general population. Two such large scale surveys from the U.S. are the Baltimore Epidemiologic Catchment Area Survey (ECA) (Eaton et al., 1989) and the National Comorbidity Survey (NCS), initially conducted in 1991 and replicated in 2001 (Kessler et al., 1994, Kessler et al., 2003). Using the Diagnostic Interview Schedule (DIS) (Robins, Helzer, Croughan, & Ratcliff, 1981) based
The cost of depression
Overall the picture painted is similar across the surveys of prevalence throughout the world. Data clearly identify depression as a major public health problem (Scott & Dickey, 2003). Depression exacts a huge cost on the individual and their personal circumstances. It contributes to enormous loss for society as well.
A recent economic review of the cost of depression reports that the direct cost of depression is accounted for by high healthcare usage, the majority of which is not the result of
The course of depression: Remission, recovery, relapse and recurrence
Early empirical studies investigating the course of depression were hindered by a lack of consensus about key points of change that were being observed in the results. This was resolved and the key change points were named and defined by a task force, see Table 1 (Frank et al., 1991).
What follows is a discussion of the research reports on the course of depression. Three large scale studies to note are firstly, the National Institute of Mental Health (NIMH) Collaborative Depression Study (CDS) (
Conclusion
The growing prevalence of depression worldwide is of concern, especially given the associated economic, societal, personal, and interpersonal costs. The global cost of depression far outweighs the cost to understanding it accurately and treating successfully those who suffer. Because depression displays high rates of lifetime prevalence, early age of onset, high chronicity, and role impairment, the WHO has ranked depression as the single most burdensome disease in the world in terms of years
Acknowledgments
Thanks to Thomas Richardson for reading an earlier draft and providing helpful comments. Thanks to Candice Aguilar for proofreading the document.
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Derek Richards is currently on career break.