Classification of depressive disorders: a multiaxial approach.

Classification of depressive disorders can be performed following the Linnaean binomial nomenclature model by defining depression as a genus and the subtypes as species. A medical classification of depressive disorders would need to be jointly inclusive and mutually exclusive between subtypes, and to provide time of onset, severity of illness, pathological process, prognosis, and treatment indications. Etiologic, phenomenologic (clinical, descriptive), statistical, and biological approaches have been used to classify depression. A convergence of these various systems in different combinations has evolved, and a consensus approach using the multiaxial system, such as DSM-III, has advanced psychiatric nomenclature to provide clinical relevance and heuristic possibilities.