Classification of mental disorders

The classification of mental disorders, also known as psychiatric nosology or psychiatric taxonomy, is a key aspect of psychiatry and other mental health professions and an important issue for people who may be diagnosed. There are currently two widely established systems for classifying mental disorders—Chapter V of the International Classification of Diseases (ICD-10) produced by the World Health Organization (WHO) and the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) produced by the American Psychiatric Association (APA). Both list categories of disorders thought to be distinct types, and have deliberately converged their codes in recent revisions so that the manuals are often broadly comparable, although significant differences remain. Other classification schemes may be in use more locally, for example the Chinese Classification of Mental Disorders. Other manuals have some limited use by those of alternative theoretical persuasions, such as the Psychodynamic Diagnostic Manual.

The widely used DSM and ICD classifications employ operational definitions. There is a significant scientific debate about the relative validity of a "categorical" versus a "dimensional" system of classification, as well as significant controversy about the role of science and values in classification schemes and the professional, legal and social uses to which they are put.

In the scientific and academic literature on the definition or categorization of mental disorders, one extreme argues that it is entirely a matter of value judgments (including of what is normal) while another proposes that it is or could be entirely objective and scientific (including by reference to statistical norms); other views argue that the concept refers to a "fuzzy prototype" that can never be precisely defined, or that the definition will always involve a mixture of scientific facts (e.g. that a natural or evolved function isn't working properly) and value judgments (e.g. that it is harmful or undesired). Lay concepts of mental disorder vary considerably across different cultures and countries, and may refer to different sorts of individual and social problems.

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