Neighborhood Ethnic Density and Psychosis in Immigrants

The paper by Veling and colleagues in the January issue (1) adds a critical piece of information to the schizophrenia literature, explaining the curious finding that the incidence of schizophrenia increases in individuals who emigrate to a new country. The authors used a clever epidemiological design to explore an association between the incidence of schizophrenia in immigrants and the ethnic density of the immigrant’s own race in a neighborhood. It was a necessary convenience that a city like The Hague exists, which has several large immigrant populations (Moroccan, Surinamese, and Turkish) living alongside native Dutch and a continuously updated municipal recording system for the ethnicity of its citizens and their parents by postal-code neighborhoods. The density of these four ethnic groups in each neighborhood was calculated, as was the social deprivation status of the neighborhood. The incidence of psychotic disorders within postal-code neighborhoods was calculated over a 7-year period. While the incidence of psychotic disorders was higher in all immigrant groups compared with native Dutch (incidence rate ratio=2.22), this difference was primarily accounted for by the dramatically higher rate of psychosis in those immigrants who lived in neighborhoods with a low density of their own ethnicity (incidence rate ratio=2.36) compared with those who lived in neighborhoods with a high density of their own ethnicity (incidence rate ratio=1.25). The risk of psychosis was unrelated to neighborhood deprivation status. These results can be interpreted to suggest that the social experience of living in an estranged environment can contribute to the onset of psychosis. Alternatively, one could propose that individuals with a propensity for psychosis seek out alienating environments. In either case, this experiment implicates the risk of an altered living context in psychosis, not “immigration” itself.