In 1952, the American Psychiatric Association first published the Diagnostic and Statistical Manual of Mental Disorders (DSM-I), marking the first attempt to approach the diagnosis of mental illness through standardized definitions and criteria. The latest edition, DSM-IV-TR, published in 2000, provides a classification system that attempts to separate mental illnesses into diagnostic categories based on descriptions of symptoms (that is, what people say and do as a reflection of how they think and feel) and on the course of the illness. The next revision, DSM-5, is expected to be published in mid-2013. This revision is expected to describe mental disorders along a continuous spectrum of symptoms, rather than classifying them by categories.
The International Classification of Disease, 10th Revision, Clinical Modification (ICD-10-CM), a book published by the World Health Organization, uses diagnostic categories similar to those in the DSM-IV-TR. This similarity suggests that diagnoses of specific mental illnesses are becoming more standard and consistent throughout the world.