sukanta saha david chant joy welham john mcgrath a systematic review of the prevalence of...
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Sukanta Saha David ChantJoy WelhamJohn McGrath
A systematic review of the prevalence of schizophrenia
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Schizophrenia is comprised of groups of brain disorders characterized by symptoms such as hallucinations, delusions, disorganized communication, poor planning, reduced motivation, and blunted affect.
While the incidence of the disorder is relatively low (median value 15.2 per 100,000 persons per year), the condition is a major contributor to the global burden of disease.
The substantial burden of schizophrenia results from: a) its typical onset in early adulthood, and b) despite optimal treatment, about two thirds of affected individuals have persisting or fluctuating symptoms.
Understanding the prevalence of schizophrenia has important implications for both health service planning and risk factor epidemiology.
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Aims
To systematically identify and collate studies of the prevalence of schizophrenia
To summarize variation in time, place and person by examining the distribution of these estimates of prevalence
To explore factors which may influence prevalence estimates
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Outline
• Types of prevalence
• Research questions
• Methods
• Key results
• Caveats and Conclusions
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Ways to measure prevalencePrevalence the proportion of a population who have
schizophrenia at a point or period in time
Point prevalence the proportion of individuals who have schizophrenia at a given point in time (e.g. 1 day or 1 week)
Period prevalence the proportion of individuals who have schizophrenia during a specified period of time (e.g. one year)
Lifetime prevalence the proportion of individuals in the population who have ever had schizophrenia, who are alive on a given day
Lifetime Morbid Risk the probability of a person developing the disorder during a specified period of their life or up to a specified age
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The prevalence of schizophrenia:Research questions
• Different types of prevalence• Sex difference
Males vs females
• Migrant status Migrants vs native born
• Urbanicity Urban born vs rural born
• Developed vs developing countries• Quality of methods
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Types of prevalence studies
• Population-based groups
‘Core studies’
Inpatient-Census-Derived data
• Population sub-groups– Migrant studies– Other special groups
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Methods: systematic review
• Electronic data search– Medline, PsychoInfo, Embase, LILAC
• 1965-2002 inclusive• (schizo* OR psycho*) AND (incidence OR
prevalence)• Review article bibliography• Wrote to authors
Screen abstract and reviewed papers to cull irrelevant citations
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Estimates and discrete data
Non-overlapping Sex Male, Female
Overlapping
Examples:Age eg. all ages or age 15-54Diagnosis eg. Catego S+ or SPO + clinicalSite overlap eg. Denmark or Copenhagen Epoch overlap eg. 1990-92 or 1989-91
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Data analysis: example cumulative distribution
Rate per 1,000
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Results
Strategy Number of papers
PCT
Electronic search 1112 85
Manual reference check
144 11
Contact authors 53 4
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Results (2)
After review– 188 studies from 46 countries – 1,721 prevalence estimates– 154,140 potentially overlapping cases
Types of studies – Core studies = 132– Migrant studies = 15– Other special groups = 41
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Core Prevalence StudiesPoint prevalence
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Core Prevalence StudiesPeriod prevalence
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Core Prevalence StudiesLifetime prevalence
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Core Prevalence StudiesLifetime Morbid Risk
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Core Prevalence StudiesUnspecified
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Core Prevalence StudiesInpatient census prevalence
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Sex differences
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Male : female estimate ratio
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Migrant statusmigrant:native population ratio
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Urban-rural differences
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Economic status of country
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Economic status of country Male:female
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Quality score
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Other special groupsElderly 10Ethnic groups 8Aborigines 4Religious groups 5Homeless 4Children & adolescents 3Students 2Twins 1Industrial workers 1Different castes 1An isolate pedigree 1
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Key findings
Like incidence, the prevalence of schizophrenia is variable across sites/groups:
-it ranges from 3-7 per 1,000 persons, depending on the type of prevalence estimate
-is higher in migrants vs native bornAlso countries from the developing world have a lower prevalence
of schizophrenia Unlike incidence, the prevalence of schizophrenia- does not vary between the sexes - but there is substantial
variation between sites- is not higher in urban versus rural settings
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Discussion
• 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
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Conclusions
Many people with schizophrenia have persistent symptoms
It is estimated that even given the best interventions, 3/4 of the burden of schizophrenia would remain
This demands additional applied and basic etiological research
Paradoxes like the differences between incidence and prevalence in sex differences and urban-rural settings demand further research