The incidence of psychotic disorders: only the tip of the iceberg?

The incidence of psychotic disorders such as schizophrenia varies across person and place. We’ve known this since at least the 1930s, when Faris and Dunham demonstrated that rates were higher in inner-city areas in Chicago compared with the suburbs, and in African-Americans compared with their white American counterparts1. This certainty was lost as the twentieth century wore on. The WHO ten-country study, published in 1992, demonstrated a 2.5 times differences in ‘broad schizophrenia’ (non-affective disorders)2 but this study was widely interpreted to indicate that schizophrenia was one of those disorders that is uniquely invariant across cultures