The epidemiology of schizophrenia.

Depending on the criteria used to diagnose schizophrenia, the incidence, prevalence and morbidity risk figures vary. Schizophrenia is probably a group of diseases with separate etiology for which biological markers are still lacking. Genetics and environment both play a part in schizophrenia, but their roles have not been specified. The illness starts in early adult life and is precipitated in vulnerable people by biopsychosocial stress. Historical, demographic, and evolutionary considerations suggest the possibility of a viral pathogen. Birth trauma and family environment also play a role. Schizophrenia usually involves a marked personality change and there are many secondary effects of illness. Improvement generally occurs after many years.