Incidence of schizophrenia in ethnic minorities in London: ecological study into interactions with environment

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Abstract
Objective: To determine whether the incidence of schizophrenia among people from non-white ethnic minorities is greater in neighbourhoods where they constitute a smaller proportion of the total population. Design: Ecological design including retrospective study of case records to calculate the incidence of schizophrenia in the ethnic minority population across electoral wards and multi-level analysis to examine interaction between individuals and environment. Setting: 15 electoral wards in Camberwell, South London. Participants: All people aged 16 years and over who had contact with psychiatric services during 1988-97. Main outcome measure: Incidence rates of schizophrenia according to Research Diagnostic Criteria. Results: The incidence of schizophrenia in non-white ethnic minorities increased significantly as the proportion of such minorities in the local population fell. The incidence rate ratio varied in a dose-response fashion from 2.38 (95% confidence interval 1.49 to 3.79) in the third of wards where non-white ethnic minorities formed the largest proportion (28-57%) of the local population to 4.4 (2.49 to 7.75) in the third of wards where they formed the smallest proportion (8-22%). Conclusion: The incidence of schizophrenia in non-white ethnic minorities in London is greater when they comprise a smaller proportion of the local population. What is already known on this topic An increased incidence of schizophrenia has been reported in several ethnic minorities in the United Kingdom Biological risk factors do not seem to explain this Reports from the United States have shown an association between the proportion of an ethnic minority living in an area and their admission rates for mental illness in general What this study adds The lower the proportion of non-white ethnic minorities in a local area the higher the incidence of schizophrenia in those minorities