Incidence of schizophrenia and other psychoses in England, 1950-2009: a systematic review and meta-analyses

Abstract

Background: We conducted a systematic review of incidence rates in England over a sixty-year period to determine the extent to which rates varied along accepted (age, sex) and less-accepted epidemiological gradients (ethnicity, migration and place of birth and upbringing, time).

Objectives: To determine variation in incidence of several psychotic disorders as above.

Data sources: Published and grey literature searches (MEDLINE, PSycINFO, EMBASE, CINAHL, ASSIA, HMIC), and identification of unpublished data through bibliographic searches and author communication.

Study eligibility criteria: Published 1950-2009; conducted wholly or partially in England; original data on incidence of non-organic adult-onset psychosis or one or more factor(s) pertaining to incidence.

Participants: People, 16-64 years, with first -onset psychosis, including non-affective psychoses, schizophrenia, bipolar disorder, psychotic depression and substance-induced psychosis.

Study appraisal and synthesis methods: Title, abstract and full-text review by two independent raters to identify suitable citations. Data were extracted to a standardized extraction form. Descriptive appraisals of variation in rates, including tables and forest plots, and where suitable, random-effects meta-analyses and meta-regressions to test specific hypotheses; rate heterogeneity was assessed by the I²-statistic.

Results: 83 citations met inclusion. Pooled incidence of all psychoses (N = 9) was 31.7 per 100,000 person-years (95%CI: 24.6-40.9), 23.2 (95%CI: 18.3-29.5) for non-affective psychoses (N = 8), 15.2 (95%CI: 11.9-19.5) for schizophrenia (N = 15) and 12.4 (95%CI: 9.0-17.1) for affective psychoses (N = 7). This masked rate heterogeneity (I²: 0.54-0.97), possibly explained by socio-environmental factors; our review confirmed (via meta-regression) the typical age-sex interaction in psychosis risk, including secondary peak onset in women after 45 years. Rates of most disorders were elevated in several ethnic minority groups compared with the white (British) population. For example, for schizophrenia: black Caribbean (pooled RR: 5.6; 95%CI: 3.4-9.2; N = 5), black African (pooled RR: 4.7; 95%CI: 3.3-6.8; N = 5) and South Asian groups in England (pooled RR: 2.4; 95%CI: 1.3-4.5; N = 3). We found no evidence to support an overall change in the incidence of psychotic disorder over time, though diagnostic shifts (away from schizophrenia) were reported.

Limitations: Incidence studies were predominantly cross-sectional, limiting causal inference. Heterogeneity, while evidencing important variation, suggested pooled estimates require interpretation alongside our descriptive systematic results.

Conclusions and implications of key findings: Incidence of psychotic disorders varied markedly by age, sex, place and migration status/ethnicity. Stable incidence over time, together with a robust socio-environmental epidemiology, provides a platform for developing prediction models for health service planning.

Figure 1. Flow diagram (selection strategy) of included studies.

For the present paper, we included 83 citations which were either incidence only (n = 72) or incidence and prevalence studies (n = 11). ¹See Methods section and ON2 for full details ²ASSIA: Applied Social Sciences Index & Abstracts. HMIC: Health Management Information Consortium ³Supplemental data was obtained in instances where the authors stated or alluded to the availability of additional relevant data, not originally published. These data were not entered as separate citations.

Figure 2. Reported overall incidence of various psychotic disorders in England, 1950–2009.

The incidence of different psychotic disorders is plotted for each citation which contributed a primary rate for analysis. As the diagnostic category moves from broader (i.e. all psychotic disorders) to narrower diagnostic conditions (i.e. schizophrenia, bipolar disorder) incidence rates tend to decrease. This figure also reveals absolute differences in rates between certain conditions, for example schizophrenia vs. bipolar disorder. One identified point estimate is not shown because it pertained only to rates up to age 35 years. Remaining estimates cover the full adult age range, typically until the mid-sixties.

Figure 3. Reported incidence rate ratios of schizophrenia by ethnic group and country of birth, England, 1950–2009.

Point estimates are colored by broad ethnic group. IRR are in descending order for narrow ethnic groups. Baselines: †white British; ‡white group; *Non black Caribbean; ∧UK-born. C96 did not provide data to estimate confidence intervals. i, ii, iii & iv: Upper confidence limits truncated for clarity. Actual values: i:26.2; ii: 23.4; iii: 23.6; iv: 66.5.