The act of identifying a disease or condition, mental or otherwise, through analysis of its symptoms and the use of various tests or procedures. In the United States, a commonly used source of diagnostic criteria for mental disorders is the DSM, or Diagnostic and Statistical Manual of Mental Disorders, published by the American Psychiatric Association.
Example: After administering several diagnostic tests for depression, interviewing her patient, and consulting the DSM, the psychologist concludes that the client is suffering from moderate clinical depression.
Grinnell, R. (2008). Diagnosis. Psych Central. Retrieved on May 3, 2015, from http://psychcentral.com/encyclopedia/2008/diagnosis/