Schizophrenia: epidemiology and risk factors

Two long-standing axioms in the epidemiology of schizophrenia are being re-evaluated in the light of recent research findings. The first, that the incidence of narrowly defined schizophrenia is uniform worldwide, no longer holds true: studies have demonstrated significant variation in incidence rates between and within countries, and between populations within countries. The second, that the outcome of schizophrenia is better in developing countries, is also being challenged. A consistent finding has been the high rate of schizophrenia in migrant groups in several countries, particularly the African-Caribbean population in the UK. Recent studies have overcome most of the methodological issues that caused some to question the validity of these findings, to the extent that they can now be regarded as robust. ‘Biological’ factors seem unlikely to account for these high rates, but recent findings in social psychiatry may be starting to shed light on possible causes. Factors such as prolonged childhood separation and adversity, along with later social adversity and isolation, are associated with the later development of psychosis in general, but appear to be particularly prevalent in the UK African-Caribbean population. This, in turn, may account partly for the increased incidence of schizophrenia and other psychoses in this and other migrant groups.