Evidence for geographical variations in the prevalence of schizophrenia in rural Ireland.

Geographical variations in the rate of occurrence of schizophrenia have been the subject of much speculation and controversy, but it has proved extremely difficult to establish the existence of the phenomenon within a given study area. Using current inpatient and outpatient records and information from key informants active in the community, this study sought to identify all cases of schizophrenia in 36 District Electoral Divisions, constituting a clinical catchment area of 25,178 persons in a rural Irish county. Though the overall prevalence rate (3.3 per 1000) was unremarkable, this obscured a substantial and significant variation in prevalence rates (from 0.0 to 14.3 per 1000) between District Electoral Divisions. Prevalence rates in five District Electoral Divisions made particular contributions to the overall deviation from a statistical model for random occurrences in space. The results indicate spatial inhomogeneity in the prevalence of schizophrenia in rural Ireland and imply geographical variation in environmental or genetic factor(s) of etiologic relevance.