Social environment, ethnicity and schizophrenia. A case-control study.

BACKGROUND

There is accumulating evidence that genetic and neurodevelopmental factors cannot solely account for the pathogenesis of schizophrenia. In view of the reportedly increased incidence of schizophrenia among the African-Caribbean population in Britain, we sought to establish the socio-environmental influences which distinguished African-Caribbean patients from white British and Asian patients with schizophrenia, as well as from normal population controls of the same community.

METHOD: A matched case-control study was conducted in London between 1991 and 1993. Inclusion criteria for patients was a first onset psychosis between the ages of 18 and 64. Symptoms were recorded using the Present State Examination (PSE), and a research diagnosis of schizophrenia was made using the CATEGO program. Comparisons were made on a range of demographic and socio-environmental measures between patients (n = 100: 38 African-Caribbean, 38 white and 24 Asian) and the same number of normal controls.

RESULTS

Three socio-environmental variables differentiated the African-Caribbean cases from their peers and their normal controls: unemployment, living alone and a long period of separation from either or both parents as a minor. Though all patients were much more likely than controls to be unemployed at first contact with the services (odds ratio 5.5, 95 % CI 2.59, 11.68), the odds ratio was highest among African-Caribbeans, and further conditional logistic regression analysis demonstrated that unemployment was significantly associated with the high rate of caseness among African-Caribbeans. However, the direction of cause and effect cannot be determined from this type of study. Despite the fact that African-Caribbean cases were more likely than their peers and same group controls to live alone (p < 0.05), this did not achieve significance using Fisher's Exact Test. Separation from both parents in childhood distinguished African-Caribbean cases from their controls and from cases and controls of the other ethnic groups (odds ratio 5.0, 95 % CI 1.09, 22.82). This event cannot be attributed to the premorbid manifestations of schizophrenia, nor to psychoses in the parents, and hence is a possible explanatory factor for the high incidence of schizophrenia among African-Caribbeans in Britain.

CONCLUSIONS

These findings indicate that unemployment and early separation from both parents distinguish African-Caribbeans diagnosed with schizophrenia from their counterparts of other ethnic groups as well as their normal peers, and imply that more attention needs to be focussed on socio-environmental variables in schizophrenia research.