To the Editor.—
Youssef et al1 claim to have demonstrated significant geographic variation in the prevalence of schizophrenia in a small rural county in Ireland. If this were indeed the case, extensive studies attempting to rigorously define the cause of the geographic variation would be imperative. We believe there is a serious weakness in their study, namely, the probable instability of the rates due to limited population sizes of the electoral divisions under study and the relatively rare rate of occurrence of schizophrenia. We think the authors have overstated their findings and we cannot agree that the study has demonstrated geographic variation in rates of schizophrenia, as claimed.Although the fit of the Poisson model of constant rates (×2=56.88, df=35, and P<.02) indicates that the observed variation in prevalence rates of schizophrenia among the 36 divisions is statistically significant, this variation mainly results from the
Lin SP, Goodman AB. Geographic Variations in the Prevalence of Schizophrenia. Arch Gen Psychiatry. 1992;49(11):906–907. doi:10.1001/archpsyc.1992.01820110070013
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