The continuity of psychotic experiences in the general population

Schizophrenia is a severe mental illness that affects 1 % of the population . The diagnosis is made according to current diagnostic systems of DSM-IV ( American Psychiatric Association, 1994) and ICD-10 (World Health Associatio n, 1992) on the basis of characteristic 'positive' and 'negative' symptoms. The traditional medical model assumes a categorical view of the schizophre nia syndrome and its core symptoms, in which differences between psychotic symptoms and their normal counterparts are considered to be qualitative. An alternative, dimensional approach assumes that schizophrenia is not a disc rete illness entity, but that psychotic symptoms differ in quantitative way s from normal experiences and behaviours. This paper reviews evidence for t he continuity of psychotic symptoms with normal experiences, focusing on th e symptoms of hallucinations and delusions. It concludes by discussing the theoretical and treatment implications of such a continuum. (C) 2001 Elsevi er Science Ltd.