systematic A review of the incidence of schizophrenia
John McGrath Sukanta Saha Joy Welham David Chant
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
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
Outline
Research questions Methods & Systematic reviews Key results Caveats and Conclusions
The incidence of schizophrenia: Hypotheses
Sex difference
Males > females
Migrant status
Migrants > native born
Urbanicity
Urban born > rural born
Types of incidence studies
`Core studies' Sentinel surveys Register based studies Migrant studies Cohort studies Other special groups
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
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 1989-91
Data or analysis: example cumulative distribution
Rate per 100,000
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
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
Core Incidence Studies
Sex differences
Male : female rate ratio
Migrant status
Urban-rural differences
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)
Other special groups
over age 65 twins various ethnic and/or religious subgroups students deaf individuals workers in a radiation contamination zone
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
Key findings (2)
Males > females Migrants > native born Urban...