Risk factors and confounders in the geographical clustering of schizophrenia

In response to previous reports of geographical clustering of individuals w ith psychosis, a study was carried out in Denmark utilizing the national ca se register. Two-thousand one-hundred and ninety-nine (2199) individuals wi th schizophrenia were divided by place of birth into 217 geographical areas and analyzed by age, gender, month of birth, genetic relatedness, and degr ee of urbanization of birthplace. Heterogeneity was ascertained using log-l inear Poisson regression. The greatest amount of heterogeneity was associat ed with degree of urbanization of place of birth. Heterogeneity was also as sociated with age-gender interaction and calendar period. When adjusted for these factors, there was no remaining heterogeneity, suggesting that all g eographical clustering in our study was explained by the above factors. (C) 2001 Elsevier Science B.V. All rights reserved.