Diagnosis is the process of identifying and labeling specific disease conditions. The signs and symptoms used to classify a sick person as having a disease are called diagnostic criteria. Diagnostic criteria and classification systems are useful for making clinical decisions, estimating disease prevalence, understanding the causes of disease, and facilitating scientific communication.

Diagnostic classification provides the treating clinician with a basis for retrieving information about a patient's probable symptoms, the likely course of an illness, and the biological or psychological process that underlies the disorder. For example, the DIAGNOSTIC AND STATISTICAL MANUAL (DSM) of the American Psychiatric Association (1987) is a classification of mental disorders that provides the clinician with a systematic description of each disorder in terms of essential features, age of onset, probable course, predisposing factors, associated features and differential diagnosis. Mental health professionals can use this...