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John McGrath Sukanta Saha Joy Welham David Chant

A systematic review of the incidence of schizophrenia. John McGrath Sukanta Saha Joy Welham David Chant.

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John McGrath Sukanta Saha Joy Welham David Chant

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  1. A systematic review of the incidence of schizophrenia John McGrathSukanta SahaJoy WelhamDavid Chant

  2. Schizophrenia - the most common form of psychosis – is characterised by disorders of cognition (eg paranoia), affect (mood), communication (thought disorder) and perception (eg hallucinations) – leading to a loss of contact with reality along with various forms of impaired behavior. Because schizophrenia (a) has an early onset and (b) has a relapsing or chronic course, it is a significant public health problem. It ranks in the top 10 leading causes of disability, with a burden of disease comparable to cancer and greater than heart disease. Previously the incidence of schizophrenia has been thought to be relatively uniform across time and place. The identification of variations in the incidence of schizophrenia is important in unravelling the causes of the disorder

  3. Aims To systematically review studies of the incidence of schizophrenia To examine variation in time, place and person by examining the distribution of these rates To explore a limited number of a priori hypotheses

  4. Outline • Research questions • Methods & Systematic reviews • Key results • Caveats and Conclusions

  5. The incidence of schizophrenia:Hypotheses • Sex difference Males > females • Migrant status Migrants > native born • Urbanicity Urban born > rural born

  6. Types of incidence studies • ‘Core studies’ Sentinel surveys Register based studies • Migrant studies • Cohort studies • Other special groups

  7. Methods: systematic review • Electronic data search • Medline, PsychoInfo, Embase, LILAC • 1965-2001 inclusive • (schizo* OR psycho*) AND incidence OR prevalence) also • Review article bibliography • Wrote to authors Screen abstract and reviewed papers to cull irrelevant citations

  8. Rate items and discrete data • Non-overlapping Sex Male, Female • Overlapping Age eg all ages or age 15-54 Diagnosis eg Catego S+ or Catego SPO + clinical Diagnostic categories eg DSMIV Schizophrenia or Schizophrenia + Delusional disorder Site overlap eg Denmark or Copenhagen Epoch overlap eg 1990-92 or 1989-91

  9. Data analysis: example cumulative distribution Rate per 100,000

  10. Results • Electronic search = 834 potential papers • Manual checking = 249 potential papers • Letters from 52 authors, who provided an additional 41 references Of potentially relevant papers, 74% were identified from electronic sources

  11. Results (2) • Rates based on 176,056 potentially overlapping incident cases After review • 158 were included from 32 countries • Types of studies • Core studies = 100 • Migrant studies = 24 • Cohort studies = 23 • Other special groups = 14

  12. Core Incidence Studies

  13. Sex differences

  14. Male : female rate ratio

  15. Migrant status

  16. Urban-rural differences

  17. Cohort studies • Australia (n=2) • Denmark (n=3) • Finland (n=5) • Israel (n=2) • Italy (n=1) • Sweden (n=2) • The Netherlands (n=2) • USA (n=3) • United Kingdom (n=3)

  18. Other special groups • over age 65 • twins • various ethnic and/or religious subgroups • students • deaf individuals • workers in a radiation contamination zone

  19. Key findings • Most of the distributions are ‘data rich’ • Variation • Asymmetrical • Long upper tail (>25% rates) • Median 15.2 (10-90% 7.7- 43.0) per 100,000 • Five-fold range within the 10-90% quantiles

  20. Key findings (2) • Males > females • Migrants > native born • Urban > mixed urban/rural • Schizophrenia has a varied and detailed epidemiological landscape

  21. Caveats • Comparisons in systematic reviews should be planned, based on directional hypotheses & limited to a reasonable number • Systematic reviews are best suited to hypothesis-generation • Geographical boundaries are administrative • Mostly ‘treated’ incidence

  22. Conclusions There is a wealth of data available on the incidence of schizophrenia. Studies come from many countries, with many different methodological features, and conducted over several decades. 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. Thus these data may provide leads for further research into risk factors

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