Impact of ethnic density on adult mental disorders: narrative review.

Background: The 'ethnic density hypothesis' is a proposition that members of ethnic minority groups may have better mental health when they live in areas with higher proportions of people of the same ethnicity. Investigations into this hypothesis have resulted in a complex and sometimes disparate literature.

Aims: To systematically identify relevant studies, summarise their findings and discuss potential explanations of the associations found between ethnic density and mental disorders.

Method: A narrative review of studies published up to January 2011, identified through a systematic search strategy. Studies included have a defined ethnic minority sample; some measure of ethnic density defined at a geographical scale smaller than a nation or a US state; and a measure ascertaining mental health or disorder.

Results: A total of 34 papers from 29 data-sets were identified. Protective associations between ethnic density and diagnosis of mental disorders were most consistent in older US ecological studies of admission rates. Among more recent multilevel studies, there was some evidence of ethnic density being protective against depression and anxiety for African American people and Hispanic adults in the USA. However, Hispanic, Asian-American and Canadian 'visible minority' adolescents have higher levels of depression at higher ethnic densities. Studies in the UK showed mixed results, with evidence for protective associations most consistent for psychoses.

Conclusions: The most consistent associations with ethnic density are found for psychoses. Ethnic density may also protect against other mental disorders, but presently, as most studies of ethnic density have limited statistical power, and given the heterogeneity of their study designs, our conclusions can only be tentative.