The course of schizophrenic psychoses: what do we really know? A selective review from an epidemiological perspective.

There is only a limited amount of definite knowledge on the course of schizophrenic psychoses, although 100 years have passed since they were first described by Kraepelin as "Dementia praecox". The main reason for this is that most studies done thus far suffer from more or less serious methodological shortcomings: samples were often highly selective; investigations were often not direct, not prospective and almost never continuous, which would be of utmost importance in an episodic disease such as schizophrenia; assessments in older studies were neither standardized nor tested for validity or reliability; in more recent studies they were often not conducted by experienced psychiatrists; patients who refused to participate or who died during the study period were widely neglected. Nevertheless, we have learned that schizophrenic psychoses do not have a steadily deteriorating course ending in "dementia". On the contrary, the course of these psychoses seems very heterogeneous. Due to their methodological shortcomings, studies done thus far even seem to have underestimated heterogeneity by partly neglecting patients with very good outcome, on the one hand, and very poor outcome, on the other hand.