[The disease "picture" of schizophrenia. Change due to operational diagnostic systems and effects on research in epidemiology and disease course].

Both in classical German psychiatry and in the contemporary operationalized diagnostic systems schizophrenia is conceptualised as a categorical disorder, the presence or absence of which can be verified dichotomously. Empirical results, however, suggest that schizophrenia might be a dimensional disorder. The categorical perspective has advantages for epidemiological research; it produced important results like the finding of a world-wide equal incidence of schizophrenia. Increasing importance is attributed to the definition of criteria, especially those of duration, which is arbitrary in many aspects. Results of research concerning the course of illness and sex distribution vary, depending on the definition of criteria, giving rise to different etiological hypotheses.