Sukanta Saha David ChantJoy WelhamJohn McGrath

A systematic review of the prevalence of schizophrenia

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.

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

Outline

• Types of prevalence

• Research questions

• Methods

• Key results

• Caveats and Conclusions

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

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

Types of prevalence studies

• Population-based groups

‘Core studies’

Inpatient-Census-Derived data

• Population sub-groups– Migrant studies– Other special groups

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

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

Data analysis: example cumulative distribution

Rate per 1,000

Results

Strategy Number of papers

PCT

Electronic search 1112 85

Manual reference check

144 11

Contact authors 53 4

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

Core Prevalence StudiesPoint prevalence

Core Prevalence StudiesPeriod prevalence

Core Prevalence StudiesLifetime prevalence

Core Prevalence StudiesLifetime Morbid Risk

Core Prevalence StudiesUnspecified

Core Prevalence StudiesInpatient census prevalence

Sex differences

Male : female estimate ratio

Migrant statusmigrant:native population ratio

Urban-rural differences

Economic status of country

Economic status of country Male:female

Quality score

Other special groupsElderly 10Ethnic groups 8Aborigines 4Religious groups 5Homeless 4Children & adolescents 3Students 2Twins 1Industrial workers 1Different castes 1An isolate pedigree 1

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

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

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