meta-analysis: an introduction george a. kelley, da, facsm school of medicine, dept. of community...
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Meta-Analysis: An Introduction
George A. Kelley, DA, FACSMSchool of Medicine,
Dept. of Community Medicine,
West Virginia University,
Morgantown, WV
Bio Funding Publications
Interest and Excitement for Meta-Analysis
Proliferation of information on health-related disease
Need to try and “make sense out of nonsense”
Enjoyment for combining and analyzing data
Learning Objectives
Identify what meta-analysis isIdentify the advantages and
different types of meta-analysesIdentify the steps for conducting a
meta-analysis of summary data
Performance Objectives
Define meta-analysisList and describe the advantages
and types of meta-analyses List and describe the steps
necessary for conducting a meta-analysis of summary data
Major Topics Covered
I. Overview of Meta-Analysis
II. Steps for Conducting A Meta-Analysis
I. Overview of Meta-Analysis
A. Meta-Analysis Defined
B. Advantages of Meta-Analysis
C. Types of Meta-Analyses
A. Meta-Analysis – Combining the results from many studies dealing with the same topic.
B. Advantages of Meta-Analysis
1. Study question specific & narrow
2. Data collection comprehensive & specific
3. Study selection based on uniformly applied criteria
4. Data synthesis quantitative
C. Types of Meta-Analyses
1. Summary Data
2. Individual Patient Data
II. Steps for Conducting A Meta-Analysis
A. Data SourcesB. Study SelectionC. Data AbstractionD. Statistical Analysis
A. Data Sources
1. Computer searches
2. Cross-referencing
3. Hand-searching
4. Expert(s) to review list
Data Sources-Example
- Computer searches (Medline, Embase, Sport Discus, Current Contents, Dissertation Abstracts)
- Cross-referencing from review and original articles
- Experts to review list (Drs. James Hagberg & Doug Seals)
B. Study Selection
1. Study designs2. Subjects3. Publication types4. Languages5. Interventions6. Time Frame
Study Selection-Example
- RCTs or CTs with a nonexercise control group
- Progressive resistance training as the only mode of training
- Females > 18 years of age- Journal articles, dissertations, &
masters theses published in English
Study Selection (cont.)
• Studies published & indexed between January 1966 and December 1998
• Bone mineral density assessed at femur, spine, and/or radius
• Training studies > 16 weeks
C. Data Abstraction
1. Number of items coded2. Inter-coder bias3. Items coded
Data Abstraction – Example
242 possible items coded Data independently abstracted
by first two authors Every data point reviewed for
accuracy and consistency Major characteristics coded –
study, physical, exercise, primary & secondary outcomes
D. Statistical Analysis
1. Choice of metric
2. Choice of model/ heterogeneity
3. Publication bias
4. Study quality
5. Moderator analysis
1. Choice of Metric
a. Original
b. Standardized mean difference (Mean/Standard Deviation)
2. Choice of Model/ Heterogeneity
a. Fixed Effects
b. Random Effects
Metric, Model, & Heterogeneity - Example
Study N TE + SD 95% CI
1 68 -2 + 4 -3 to –1
2 92 -1 + 4 -2 to 0
3 78 -4 + 3 -5 to -3
3. Publication Biasa. Graphical methods
b. Quantitative methods
Funnel Plot - Example
0
20
40
60
80
100
120
-25 -20 -15 -10 -5 0 5 10 15 20 25
Systolic ES (mmHg)
Sam
ple
S
am
ple
S
ize
Siz
er = 0.50, p = 0.007
4. Study Quality
a. Difficult to assess
b. Interpret with caution
c. Numerous scales and checklists available
5. Moderator Analysis
a. Categorical Analysis
b. Regression Analysis
Categorical Analysis - Example
Group N + SD 95% CI Qb(p)
USA Other
17 11
-1 + 3 -4 + 4
-3 to -1 -6 to -2
4.00(0.04)*
RCT CT
7 21
-2 + 3 -2 + 4
-3 to -1 -5 to 1
0.08(0.77)
Note: RCT, randomized controlled trials, CT, controlled trials; N, number of effect sizes; * means significantly different at P<0.05
Regression - Example
Variables N r r2 r2adj SE p
IBMI, ISBP 18 0.75 0.57 0.51 3.47 0.002
Notes: IBMI means initial body mass index (kg/m2); ISBP means initial systolic blood pressure (mmHg); N means number of effect sizes.
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