It seems eminently plausible that there should be variation in the incidence of psychoses across the globe. Nonetheless, we know little about the nature and scope of such variation, and what we do know is often misunderstood. The landmark World Health Organization Ten Country Study,1 published in 1992, pioneered a strategy for comparing the incidence of treated cases of psychoses across multiple settings in different countries. It obtained incidence rates for schizophrenic disorders from 8 diverse settings, including rural and urban Chandigarh, India; Nagasaki, Japan; European locations; and North American settings. The authors described the rates of schizophrenic disorders as “surprisingly similar”1(p90) and further remarked that this finding would “not easily lend itself to an interpretation.”1(p91) They did not claim that schizophrenia has the same incidence across the globe, a common misunderstanding of the study. (Indeed, Chandigarh was the only site in a low-income country that yielded any incidence rates1; in later analyses, a distinctive psychotic disorder subtype was found to be more common there.2) A subsequent comprehensive review3 of a large number of studies concluded that the incidence of schizophrenia shows substantial variation by place. A specific example was higher incidence rates in more urban locales. However, to our knowledge, there has not been another attempt to date to demonstrate variation in psychosis incidence within a single study of multiple locations in several countries using comparable methods in each place.
Susser E, Martínez-Alés G. Putting Psychosis Into Sociocultural Context: An International Study in 17 Locations. JAMA Psychiatry. 2018;75(1):9–10. doi:10.1001/jamapsychiatry.2017.3541
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