Introduction to meta-analysis

1. How to do Meta Analysis
SHARANBASAPPA
School of Natural Product Studies
Jadavpur University, Kolkata-
700032
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2. Contents
• What is a Meta-Analysis?
• How to Do a Meta-Analysis
• Limitations to Meta-Analysis
• Summarizing
• References
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3. Definition
“The analysis of analyses”
• Quantitative approach for systematically
combining results of previous research to
arrive at conclusions about the body of
research
• The application of statistical procedures to
examine tests of a common hypothesis
from more than one study.
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4. The popularity of meta analyses
0
500
1000
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2000
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93-94 94-95 95-96 96-97 97-98 98-99 99-00 2000-1 2001-2 2002-3 2003-4
NumberofPublications
Year of Publications
publications
Number of Meta Analysis publications are steadily increasing since 1993. We
graphed the counts of journal articles included “meta analysis” as “publication
type” from Pubmed, from years 1993 through 2004.
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5. How to do Meta-analysis
Four Steps
• Identify your studies
• Determine eligibility of studies
–Inclusion: which ones to keep
–Exclusion: which ones to throw out
• Abstract Data from the studies
• Analyze data in the studies statistically
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6. Identify your studies
• Be methodical: plan first
• List of popular databases to search
–Pubmed/Medline
–Embase, Scopus, Science direct, Science
finder
–Cochrane Review/Trials Register
• Other strategies you may adopt
–Hand search (go to the library...)
–Personal references, and emails
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7. How to Search for literature
• Formulate your question appropriately
• If you are searching pubmed
–Use Medical Subject Headings (MeSH)
[1]
–Lookup word in text word, abstract,
title [2]
–Combine [1] with [2] using Boolean
logic
–Set up proper filters
• For Others, use text word, abstract 7

8. Example: Research Issue
• Let's say we want to know whether
Withania somnifera is protective in
brain oxidative stress in rodents. How
should we set up a search strategy? We will
search pubmed only
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9. The Search
• “Withania somnifera”[text word] OR
“oxidative stress”[text word] produces ALL
articles that contain EITHER withania
somnifera OR oxidative stress anywhere in
the text – inclusive, many
• Withania somnifera [text word] AND
“oxidative stress” [text word] will capture
only those subsets that have BOTH Withania
somnifera AND oxidative stress anywhere in
the text – restrictive, few
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10. Plan of Action
ARE THE STUDIES ELIGIBLE FOR MA (STEP I)?
DISCARD
YES
NO
ENTER INTO A SPECIFIED FORMAT
ABSTRACT THE DATA
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11. Search strategy
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12. How to Abstract Data: Guidelines
• Create a spreadsheet (Excel, or Open Office
Calc)
• For each study, create the following
columns:
– name of the study
– name of the author, year published
– number of animals which received withania
somnifera treatment
– number of animals in control group
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13. Analyze Data Statistically
• Combine data to arrive at a summary, 3 measures
– Effect Size (Odds Ratio)
– Variance with 95% Confidence Interval
– Test of heterogeneity
• Two Graphs
– Forest Plot
– Funnel Plot
• Examine why the studies are heterogeneous, if they
are
• Use Statistical Packages, several choices
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14. Forest plot
Effect of WS on LPO in rodent brain oxidative stress
Effect of WS on catalase in rodent brain oxidative stress
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15. Limitations/Issues in meta analysis
• Choosing a model
–Fixed effects model or random
effects?
• Bias in meta analysis
–poor quality of studies
–publication bias
• Quality control in meta analysis
–QUOROM guidelines
• Statistical Software for meta analysis 15

16. Statistical Software for Meta Analysis
• Huge Checklist
[http://faculty.ucmerced.edu/wshadish/]
• Free Software:
–EpiMeta: from Epi Info
–Revman: from Cochrane Collaboration
–“meta” package in R for statistical
computing
• Non-free
–meta module in STATA 16

17. Summarizing...
• Defined meta analysis
–quantitative research synthesis
• Outlined basic steps
–Information retrieval
–Data Abstraction
–Data Analysis
–Model Selection: Fixed Effects or
Random effects
• Outlined some issues and listed
software 17

18. References
• Vesterinen, H.M., Sena, E.S., Egan, K.J., Hirst, T.C., Churolov, L., Currie,
G.L., Antonic, A., Howells, D.W., Macleod, M.R., 2014. Meta-
analysis of data from animal studies: A practical guide. Journal of
Neuroscience Methods. 221, 92-102.
• Neyeloff, J.L., Sandra C Fuchs, S.C., Moreira, L.B., 2012. Meta-analyses
and Forest plots using a Microsoft excel spreadsheet: step-by-step guide
focusing on descriptive data analysis. BMC Research Notes. 5, 52.
• User guide. Review Manager (RevMan) [Computer program]. Version
5.2. Copenhagen: The Nordic Cochrane Centre, The Cochrane
Collaboration, 2012.
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