The prevalence of schizophrenia: a systematic review

1
The prevalence of schizophrenia a systematic
review

• Sukanta Saha
• David Chant
• Joy Welham
• John McGrath

Art work from the QCMHR Collection
2
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

3
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

4
Systematic reviews

• Past reviews
• Torrey 1987 (narrative)
• Jablensky - several reviews (narrative)
• Goldner et al. 2002 (systematic review with
  meta-analysis)
• 8 studies (1980-2000)
• Lifetime prevalence varied 13 fold
• Distribution of rates versus pooled rate

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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

6
Methods

• Electronic data searches
• Medline, PsychoInfo, Embase, LILAC
• 1965-2002 inclusive
• Index terms
• (schizo OR psycho) AND (incidence OR prevalence)

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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

8
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

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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

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The taxonomy of prevalence

• Point
• Period
• Lifetime
• Lifetime Morbid Risk (LMR)
• Not otherwise specified (NOS)
• Inpatient-Census-Derived rates

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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)

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Detailed search strategy

• Electronic databases 1112

• From bibliography 144

• Contact with authors 53

• Total studies 1309

• Not prevalence 561

• Review/commentary 190

Awaiting assessment/ unobtainable 12
Incidence study (1586)164

• Potential Prevalence Studies 388

13
Potential Incidence/Prevalence studies 388
Not population based 87
Insufficient data 48
Follow up/other studies 17
Prevalence studies 219

• LOTE
• Prevalence
• 17

Complete Overlap 26

Prison Studies 19
Total Prevalence Studies235- (2619) 191
Special Group studies 44
Migrant studies 14
Core studies 133
14
Region Nations Studies
North America 2 31
Central and South America 4 5
Europe 18 84
Africa 6 9
Asia 11 42
Australasia 4 13
15
LOTE Papers (7 Languages)

• Chinese (3)
• French (2)
• German (4)
• Italian (1)
• Japanese (3)
• Russian (3)
• Spanish (1)
• Total 17

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Prevalence of SchizophreniaCombined rates for
persons
Number of rates 141 Median value 3.3 per
1000
17
Prevalence of Schizophrenia per 1000 (persons)
n 10 Median 90 Mean
Point
Period
Lifetime
NOS
Combined
18
Prevalence of Schizophrenia per 1000 (persons)
n 10 Median 90 Mean
Point 24 2.9 4.3 10.0 5.8
Period
Lifetime
NOS
Combined
19
Prevalence of Schizophrenia per 1000 (persons)
n 10 Median 90 Mean
Point 24 2.9 4.3 10.0 5.8
Period 44 1.3 3.4 8.5 5.7
Lifetime
NOS
Combined
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Prevalence of Schizophrenia per 1000 (persons)
n 10 Median 90 Mean
Point 24 2.9 4.3 10.0 5.8
Period 44 1.3 3.4 8.5 5.7
Lifetime 31 2.1 4.0 11.0 5.6
NOS
Combined
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Prevalence of Schizophrenia per 1000 (persons)
n 10 Median 90 Mean
Point 24 2.9 4.3 10.0 5.8
Period 44 1.3 3.4 8.5 5.7
Lifetime 31 2.1 4.0 11.0 5.6
NOS 42 1.4 2.7 4.7 4.5
Combined
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Prevalence of Schizophrenia per 1000 (persons)
n 10 Median 90 Mean
Point 24 2.9 4.3 10.0 5.8
Period 44 1.3 3.4 8.5 5.7
Lifetime 31 2.1 4.0 11.0 5.6
NOS 42 1.4 2.7 4.7 4.5
Combined 141 1.5 3.3 10.0 5.4
23
Lifetime Morbid Risk per 1000 (persons)
n 10 Median 90 Mean
Lifetime Morbid Risk 27 3.1 7.2 27.1 11.9
24
Inpatient Census Derived rate per 1000 (persons)
n 10 Median 90 Mean
Inpatient census derived rate 108 0.1 2.4 10.0 6.5
25
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)
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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

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Malefemale rate ratio
Median rate ratio 1.16
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Incidence of schizophrenia
Malefemale Rate ratio 31 studies 100 rate
ratios Median (10-90 quantiles) 1.4 (0.9 to
2.4)
29
Malefemale rate ratio by nation economic status
30
Migrant vs Native born Rate Ratio (persons)
Number of rate ratios 10 Median rate ratio
1.8
31
Prevalence by Quality Score
Median value (number of rates) Lower 2.9
(54) Middle 3.0 (41) Upper 5.2 (46)
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Conclusions

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

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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

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Conclusions

• Males females for prevalence
• Developing nations
• lower prevalence
• female excess

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Acknowledgements

• Interpreters 10
• Authors who provided information 31
• Stanley Medical Research Institute

For our website for full dataset
www.qcmhr.uq.edu.au/epi