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

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.