This document discusses systematic reviews and meta-analyses. It explains that a systematic review carefully compiles and summarizes all publications on a research topic, while a meta-analysis creates a pooled statistic by combining the results of multiple studies. The process involves developing a search strategy, extracting relevant data from eligible studies, and using statistical methods to analyze the pooled results. Threats like poor study quality and publication bias must be considered.

2. Chapter 24
Tertiary Studies:
Systematic Reviews &
Meta-Analyses

3. Overview
• A systematic review is the careful compilation and
summary of all publications relevant to a particular
research topic.
• A meta-analysis creates a summary statistic (a pooled
statistic) for the results of systematically identified
articles.

4. FIGURE 24- 1
Systematic Review Process

5. Search Strategy
• After identifying a well-defined study question, the
next critical step in a systematic review or meta-
analysis is to select appropriate databases, search
terms, and search limiters.
• Once a system for identifying eligible articles is in
place, abstract databases are systematically searched
for articles that meet all the inclusion criteria.

6. FIGURE 24-2
Systematic Search
Strategy and
Counts to Report

7. Data Extraction
Once all eligible articles are identified, the content of
these articles is extracted into data extraction tables that
list descriptive characteristics like:
•The study location and study years
•The study design
•The study population and sample size
•The key findings of interest
•The strengths and limitations of the study

8. Data Extraction
• A data extraction table allows for easy compilation
and comparison of observations relevant to the study
question.
• Studies that find no statistically significant results for
an item of interest are just as valuable as those that
find a significant association.
• Publication bias occurs when articles with
statistically significant results are more likely to be
published that those with null results.

9. Meta-Analysis
• A meta-analysis pools the results of several studies
identified during a systematic review to create one
summary statistic.
• Only similar statistics from similar studies can be
pooled.
• Before pooling the data, the researcher must show
that the results of the studies are comparable.

10. Meta-Analysis
• A specialized computer software program can be used
to estimate the value of the pooled statistic and its
confidence interval.
• The contribution of each study to the pooled estimate
is usually weighted based on the sample size of the
included studies.
• The contributing studies and the summary measure
are often displayed using a forest plot.

11. FIGURE 24-3
Example of a Forest Plot

12. Meta-Analysis
Threats to the validity of a meta-analysis:
•Poor quality of included studies: The selection criteria
used during the systematic review process can eliminate
any studies of questionable validity.
•Publication bias: The possibility of publication bias
can be examined using a funnel plot.

13. FIGURE 24-4
Example of a Funnel Plot