A systematic review of the incidence of schizophrenia: the distribution of rates and the influence of sex, urbanicity, migrant status and methodology

BACKGROUND: Understanding variations in the incidence of schizophrenia is a crucial step in unravelling the aetiology of this group of disorders. The aims of this review are to systematically identify studies related to the incidence of schizophrenia, to describe the key features of these studies, and to explore the distribution of rates derived from these studies. METHODS: Studies with original data related to the incidence of schizophrenia (published 1965–2001) were identified via searching electronic databases, reviewing citations and writing to authors. These studies were divided into core studies, migrant studies, cohort studies and studies based on Other Special Groups. Between- and within-study filters were applied in order to identify discrete rates. Cumulative plots of these rates were made and these distributions were compared when the underlying rates were sorted according to sex, urbanicity, migrant status and various methodological features. RESULTS: We identified 100 core studies, 24 migrant studies, 23 cohort studies and 14 studies based on Other Special Groups. These studies, which were drawn from 33 countries, generated a total of 1,458 rates. Based on discrete core data for persons (55 studies and 170 rates), the distribution of rates was asymmetric and had a median value (10%–90% quantile) of 15.2 (7.7–43.0) per 100,000. The distribution of rates was significantly higher in males compared to females; the male/female rate ratio median (10%–90% quantile) was 1.40 (0.9–2.4). Those studies conducted in urban versus mixed urban-rural catchment areas generated significantly higher rate distributions. The distribution of rates in migrants was significantly higher compared to native-born; the migrant/native-born rate ratio median (10%–90% quantile) was 4.6 (1.0–12.8). Apart from the finding that older studies reported higher rates, other study features were not associated with significantly different rate distributions (e.g. overall quality, methods related to case finding, diagnostic confirmation and criteria, the use of age-standardization and age range). CONCLUSIONS: There is a wealth of data available on the incidence of schizophrenia. The width and skew of the rate distribution, and the significant impact of sex, urbanicity and migrant status on these distributions, indicate substantial variations in the incidence of schizophrenia

Ethnic inequalities in the incidence of diagnosis of severe mental illness in England: a systematic review and new meta-analyses for non-affective and affective psychoses.

This is a post-peer-review, pre-copyedit version of an article published in Social Psychiatry and Psychiatric Epidemiology. The final authenticated version is available online at: https://doi.org/10.1007/s00127-019-01758-yPURPOSE: Although excess risks particularly for a diagnosis of schizophrenia have been identified for ethnic minority people in England and other contexts, we sought to identify and synthesise up-to-date evidence (2018) for affective in addition to non-affective psychoses by specific ethnic groups in England. METHODS: Systematic review and meta-analysis of ethnic differences in diagnosed incidence of psychoses in England, searching nine databases for reviews (citing relevant studies up to 2009) and an updated search in three databases for studies between 2010 and 2018. Studies from both searches were combined in meta-analyses allowing coverage of more specific ethnic groups than previously. RESULTS: We included 28 primary studies. Relative to the majority population, significantly higher risks of diagnosed schizophrenia were found in Black African (Relative risk, RR 5.72, 95% CI 3.87-8.46, n = 9); Black Caribbean (RR 5.20, 95% CI 4.33-6.24, n = 21); South Asian (RR 2.27, 95% CI 1.63-3.16, n = 14); White Other (RR 2.24, 95% CI 1.59-3.14, n = 9); and Mixed Ethnicity people (RR 2.24, 95% CI 1.32-3.80, n = 4). Significantly higher risks for diagnosed affective psychoses were also revealed: Black African (RR 4.07, 95% CI 2.27-7.28, n = 5); Black Caribbean (RR 2.91, 95% CI 1.78-4.74, n = 16); South Asian (RR 1.71, 95% CI 1.07-2.72, n = 8); White Other (RR 1.55, 95% CI 1.32-1.83, n = 5); Mixed Ethnicity (RR 6.16, 95% CI 3.99-9.52, n = 4). CONCLUSIONS: The risk for a diagnosis of non-affective and affective psychoses is particularly elevated for Black ethnic groups, but is higher for all ethnic minority groups including those previously not assessed through meta-analyses (White Other, Mixed Ethnicity). This calls for further research on broader disadvantages affecting ethnic minority people.Lankelly Chase Foundatio