Sukanta Saha David Chant Joy Welham John 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 prevalence Prevalencethe proportion of a population who have schizophrenia at a point or period in time Point prevalencethe proportion of individuals who have schizophrenia at a given point in time (e.g. 1 day or 1 week) Period prevalencethe proportion of individuals who have schizophrenia during a specified period of time (e.g. one year) Lifetime prevalencethe proportion of individuals in the population who have ever had schizophrenia, who are alive on a given day Lifetime Morbid Riskthe 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 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 Diagnosis eg. Catego S+ or SPO + clinical Site overlap eg. Denmark or Copenhagen Epoch overlap eg or

Data analysis: example cumulative distribution Rate per 1,000

Results StrategyNumber of papers PCT Electronic search Manual reference check 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 Studies Point prevalence

Core Prevalence Studies Period prevalence

Core Prevalence Studies Lifetime prevalence

Core Prevalence Studies Lifetime Morbid Risk

Core Prevalence Studies Unspecified

Core Prevalence Studies Inpatient census prevalence

Sex differences

Male : female estimate ratio

Migrant status migrant:native population ratio

Urban-rural differences

Economic status of country

Economic status of country Male:female

Quality score

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