A meta-analysis of the risk for psychotic disorders among first- and second-generation immigrants

Background. There is increasing acceptance of migration as a risk factor for schizophrenia and related disorders; however, the magnitude of the risk among second-generation immigrants (SGIs) remains unclear. Generational differences in the incidence of psychotic disorders among migrants might improve our understanding of the relationship between migration, ethnicity and psychotic disorders. This meta-analysis aimed at determining the risk of psychotic disorders among SGIs in comparison with non-migrants and first-generation immigrants (FGIs). Method. Medline, EMBASE and PsycINFO databases were searched systematically for population-based studies on migration and psychotic disorders published between 1977 and 2008. We also contacted experts, tracked citations and screened bibliographies. All potential publications were screened by two independent reviewers in a threefold process. Studies were included in the meta-analysis if they reported incidence data, differentiated FGIs from SGIs and provided age-adjusted data. Data extraction and quality assessment were conducted for each study. Results. Twenty-one studies met all inclusion criteria. A meta-analysis of 61 effect sizes for FGIs and 28 for SGIs yielded mean-weighted incidence rate ratios (IRRs) of 2.3 [95% confidence interval (CI) 2.0-2.7] for FGIs and 2.1 (95% CI 1.8-2.5) for SGIs. There was no significant risk difference between generations, but there were significant differences according to ethno-racial status and host country. Conclusions. The increased risk of schizophrenia and related disorders among immigrants clearly persists into the second generation, suggesting that post-migration factors play a more important role than pre-migration factors or migration per se. The observed variability suggests that the risk is mediated by the social context.