Psychiatric diagnosis has long been criticized as ambiguous and unreliable. Some diagnoses have been based on subjective, unverifiable, intrapsychic phenomena, whereas others have been heterogeneously broad.

Modern diagnosis attempts to avoid these pitfalls through the use of the 4th edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) (1), which identifies each disorder by a unique specific collection of symptoms. (Note: throughout this text, the term “DSM” will be used to represent the most recent edition, DSM-IV-TR.) It defines a limited number of identifiable (although possibly overlapping) psychiatric disorders and contains specific diagnostic criteria for each diagnosis. One matches facts from a particular patient’s history and clinical presentation with criteria from a likely diagnosis, and if an adequate number are met (a polythetic diagnosis; not all the criteria are needed to make the diagnosis), that diagnosis should be made. Each disorder has a unique set of these “operationally defined” diagnostic criteria. Multiple diagnoses are permitted, and each general group of disorders has one disorder, “Not Otherwise Specified” (NOS), that allows placement of the (often many) patients who have unusual presentations. In addition, some disorders have subtypes, which are mutually exclusive (e.g., paranoid schizophrenia) or specifiers that are not (may change with time; e.g., mild, moderate, and severe, or in full remission) or both. Finally, it is okay to make a provisional (you are not sure) or a deferred (not enough information) diagnosis.

For example, a patient who (a) has been having delusions and auditory hallucinations that (b) have impaired social relations and functioning at work (c) for at least 6 months and who is without evidence of (d) a general medical condition or (e) prominent symptoms of a major mood disorder must be given the diagnosis of schizophrenia. If the patient also has (f) a flat, inappropriate, or
silly affect and (g) disorganized speech and behavior, an additional diagnosis of “disorganized” subtype should be made.