Transcript Meta Analysis

Meta Analysis
MAE Course 2005
Meta-analysis
• The statistical combination and analysis
of data from separate and independent
studies to determine if there is an
association between exposure and
outcome and the size of this effect
Systematic Overview Vs. Overview
• Qualitative vs. quantitative
• Literature reviews
• Statistical power and precision
Focus of Meta-analysis
• Direction of the effect across studies
• Magnitude of the effect across
studies
• Traditional methods (significance
testing) not well suited
Steps in Conducting a Metaanalysis
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Background of the problem
Develop a hypothesis
Study Inclusion criteria
Exclusion criteria
Results
–Participant characteristics
–Interventions or exposures
Advantages of Meta-analysis
• Systematic means of reviewing findings of
multiple studies
• May be used for a large number of studies
• May identify significant findings and
relationships not apparent utilizing other
means (i.e. “false negative” results)
Weaknesses of Meta-analysis
• “Comparability” of studies is sometimes
difficult to assess
• Publication bias
– “negative” studies may not be found
• Qualitative distinctions between studies
• Requires significant effort
• Methodological problems in original
studies
Example
Meta-analysis of studies on individual
consumption of chlorinated drinking water
and bladder cancer
C M Villanueva, F Fernández, N Malats, J O Grimalt, M
Kogevinas
J Epidemiol Community Health 2003;57:166–173
Study Objectives
• To evaluate whether consumption of
chlorinated drinking water is associated with
bladder cancer
Methods
• Bibliographic search
• 8 case control and cohort studies selected
• Looked at individual consumption of chlorinated
water and incidence of bladder cancer
• Risk estimates extracted
• Meta analysis performed for two exposure levels
and of the dose-response regression slopes
RESULTS
Ever Consumed Chlorinated Water
Long Term Chlorinated Water
Results
• This meta-analysis indicates that
consumption of chlorinated drinking water
is associated with a moderately increased
risk of bladder cancer.
Some Limitations of This MetaAnalysis
• Publication bias
• Chemical mixtures
• Exposure categories among studies may
be different