Psychiatric Epidemiology

Diagnosis

Psychiatric disorders include disturbances of thinking, such as schizophrenia, dementia, and mental retardation; disturbances of feeling, such as bipolar disorder, anxiety, and depression; and disturbances of acting, such as alcohol and drug disorders and antisocial disorders. Important childhood psychiatric disorders include autism, depression, and attention deficit disorders. Psychiatric disorders always involve biological or neurological adaptation of some sort and often include disruption of social life as well. These disorders are among the most disabling in the world, accounting for higher percentages of disability-adjusted life years than most other categories of disorder.

The diagnosis of psychiatric disorder is made almost totally on the basis of observed symptoms and behaviors because, to date, no biomarkers or laboratory tests are conclusive in diagnosis. The most commonly used diagnostic systems in psychiatry are the Diagnostic and Statistical Manual of Mental Disorders (DSM) and the International Classification of Diseases (ICD). Since its birth in 1952, DSM has been revised a number of times, with the most recent version being DSM-IV. DSM-V is expected in the near future. The number of psychiatric disorders listed increased from 159 in DSM-II, to 227 in DSM-III, to 357 in DSM-IV, and more are expected in DSM-V. The number of disorders has increased with revisions of the ICD also. As a result of the increasing numbers of diagnoses, as expected, the number of comorbid diagnoses also increased. This makes it more challenging to determine independent etiologies or measure an impact from a single disorder.

The use of standard criteria to define a mental disorder allows measurement of prevalence, related impairments, financial burden, and resulting mortality, and also makes it possible to compare these features across different regions, sex, and ethnic groups, as well as groups defined by other characteristics. But despite the many advances that have been accomplished in classifying mental disorders since the 1950s, case definitions are still controversial. Since the birth of the DSM and ICD, categorical diagnoses have been used for psychiatric disorders. However, many argue that mental disorders are best conceptualized as dimensional and that diagnostic thresholds may not be meaningful for etiologic [Page 849]determination. A categorical diagnostic decision is made depending on whether a patient meets or fails to meet a series of criteria, whereas a dimensional system acknowledges the continuum of symptom severity that may fall above or below a categorical diagnostic threshold. Most researchers suggest that for nosology (the systematic classification of diseases), the need for retaining categorical distinctions is compelling but that dimensional models may be more useful for clinical treatment, epidemiologic research, and policy development.

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