Nosology and statistical classification

There is a fundamental difference between nosology and a statistical classification, and the two should not be confused. The discipline of nosology uses scientific methods to arrive at a classification of psychiatric disorders and is concerned with the validity of its entities. A statistical classification aims to attain the widest compliance in spite of differences in the theoretical orientation of its users. It must therefore be atheoretical, and must represent a widely negotiated agreement between its future users. The most important statistical classification is the "International Classification of Diseases, Injuries and Causes of Death" (ICD-9) endorsed by the member states of the World Health Organization. The DSM III (Diagnostic and Statistical Manual), a newly accepted classification of the American Psychiatric Association, departs in many ways from the ICD-9, and Canada will have to decide whether adherence to ICD-9 should continue, or be replaced by the adoption of DSM III. Advantages and disadvantages of the DSM III are briefly discussed.