The prevalence of schizophrenia: a systematic review Sukanta Saha David Chant Joy Welham John McGrath Art work from the QCMHR Collection

Why is prevalence important? Estimate the burden of a disorder Administration - service planning Provides information about the interaction between incidence and course of the illness Gradients in the prevalence of a disorder can help generate risk factors

Systematic reviews Traditional methods –narrative reviews Systematic reviews –A standardized, rigorous process of finding literature and extracting data in a way that minimizes bias and errors –with or without meta-analysis

Systematic reviews Past reviews –Torrey 1987 (narrative) –Jablensky - several reviews (narrative) –Goldner et al (systematic review with meta-analysis) 8 studies ( ) Lifetime prevalence varied 13 fold: Distribution of rates versus pooled rate

Outline Distribution of various types of prevalence –Median and spread of rate items –Sensitivity analyses economic status of country quality score Male-female rate ratio –Sensitivity analysis by economic status of country Migrant-Native born rate ratio

Methods Electronic data searches –Medline, PsychoInfo, Embase, LILAC inclusive Index terms: –(schizo* OR psycho*) AND (incidence OR prevalence)

Methods Review article bibliography Writing to authors Posters at Whistler and Davos conferences Screen abstract to cull irrelevant citations Order articles for review and data extraction

Discrete rates One study may generate multiple rates –ECA study (60 rates): 5 age gr 4 rate types 2 sexes Discrete (non-overlapping) –Male = 2.1 per 1,000 –Female = 1.5 per 1,000 Overlapping –site and epoch –Age groups –Diagnostic groups

Filters for overlapping studies Several filters to identify discrete data –Filters are operationalised and explicit –“Most informative” rule Entire nation preferred over regions All ages preferred over age-specific

The taxonomy of prevalence Point Period Lifetime Lifetime Morbid Risk (LMR) Not otherwise specified (NOS) Inpatient-Census- Derived rates

Results Archived 1112 articles, book chapters or theses. 85% identified via electronic sources 11% from bibliography 4% from authors: –Interim list sent to 80 authors –Replies from 31 authors (New articles, theses, bibliographies)

Detailed search strategy n Electronic databases =1112 From bibliography = 144 Contact with authors = 53 n Total studies =1309 n Not prevalence =561 n Review/commentary =190 n Potential Prevalence Studies =388 Awaiting assessment/ unobtainable =12 Incidence study (158+6)=164

Potential Incidence/Prevalence studies = 388 Not population = 87 Not population based = 87 Insufficient data = 48 n LOTE n Prevalence n = 17 Total Prevalence Studies=235- (26+19) = 191 Complete Overlap = 26 Prevalence studies = 219 Follow up/other studies = 17 Prison Studies = 19 + Special Group studies= 44Migrant studies= 14 Core studies= 133

RegionNationsStudies North America231 Central and South America 45 Europe1884 Africa69 Asia1142 Australasia413

LOTE Papers (7 Languages) Chinese (3) French (2) German (4) Italian (1) Japanese (3) Russian (3) Spanish (1) Total = 17

Prevalence of Schizophrenia: Combined rates for persons Number of rates = 141 Median value = 3.3 per 1000

Prevalence of Schizophrenia per 1000 (persons) n10%Median90%Mean Point Period Lifetime NOS Combined

Prevalence of Schizophrenia per 1000 (persons) n10%Median90%Mean Point Period Lifetime NOS Combined

Prevalence of Schizophrenia per 1000 (persons) n10%Median90%Mean Point Period Lifetime NOS Combined

Prevalence of Schizophrenia per 1000 (persons) n10%Median90%Mean Point Period Lifetime NOS Combined

Prevalence of Schizophrenia per 1000 (persons) n10%Median90%Mean Point Period Lifetime NOS Combined

Prevalence of Schizophrenia per 1000 (persons) n10%Median90%Mean Point Period Lifetime NOS Combined

Lifetime Morbid Risk per 1000 (persons) n10%Median90%Mean Lifetime Morbid Risk

Inpatient Census Derived rate per 1000 (persons) n10%Median90%Mean Inpatient census derived rate

Prevalence by Country Group Median rate per 1000 (number of rates) Least Developed Countries =2.6 (19) Emerging = 4.2 (25) High income = 3.3 (97)

Sex differences in the prevalence of schizophrenia No significant sex difference in the prevalence of schizophrenia Median (number of rates) Males = 3.8 (61) Females = 3.2 (62) F = 0.84, p = 0.36

Male:female rate ratio Median rate ratio = 1.16

Male:female Rate ratio 31 studies 100 rate ratios Median (10-90% quantiles) 1.4 (0.9 to 2.4) Incidence of schizophrenia

Male:female rate ratio by nation economic status

Migrant vs Native born Rate Ratio (persons) Number of rate ratios = 10 Median rate ratio = 1.8 Rate ratio

Prevalence by Quality Score Median value (number of rates) Lower = 2.9 (54) Middle = 3.0 (41) Upper = 5.2 (46)

Conclusions There is a wealth of data Most of the distributions are ‘data rich’ (informative) Not normally distributed - skewed by higher values

Conclusions Median overall prevalence rate = 3.3 per 1000 Median LMR = 7.2 per 1000 “2 out of every 300 people” Spread of the data 10 – 90% quantiles: Point = 3.4 fold LMR = 9 fold

Conclusions Males = females for prevalence Developing nations lower prevalence female excess

Acknowledgements Interpreters ~ 10 Authors who provided information ~ 31 Stanley Medical Research Institute For our website for full dataset: