A meta-analysis combines results from multiple independent studies on the same topic to obtain an overall quantitative estimate of an intervention's effect. It increases statistical power and generalizability. Key steps include formulating the problem, searching literature comprehensively, coding and assessing study quality, statistical analysis, and interpretation. A thorough literature search is crucial, requiring weeks of effort across various databases and sources. Unpublished studies, though most valuable due to publication bias, must also be sought through dissertations, conferences, trials registries, and institutional repositories. Librarians can provide assistance in the search process.

1. So you want to do a
meta-analysis . . .
Cooper Library Drop-In Workshop
Peggy Tyler

2. What is it?
• A meta-analysis combines results from many independent
studies of the same problem and obtains a quantitative
estimate of the overall effect of a particular intervention or
variable on a defined outcome.
• Meta analysis reports findings in terms of effect sizes. The
effect size provides information about how much change is
evident across all studies.
• A wide variety of questions can be investigated, as long as a
reasonable body of primary research studies exist

3. Why do it?
• “True” effect size/Strength in numbers
• Increases statistical power for more precise estimate
• Strength in diversity
• Generalizability across variety of
participants, settings, instruments
• Identification of moderating variables

4. Steps
• Formulate the problem
• Search the literature
• Code the data
• Quality assessment
• Statistical analysis
• Follow-up analyses based on results
• Interpretation

5. The literature is your data
• Completeness of literature search is crucial
• Allow for weeks of effort and communication with far-flung
libraries/authors/publishers
• Keep VERY good records of what you have searched
(keywords, authors, etc.) and where you have searched and
what articles you have found, downloaded, printed, ordered,
etc. A literature searching journal is a very good idea.

6. Published data
• Subject databases
• Choose keywords and look for subject headings
• Search authors and relevant tests/measures/acronyms/
instruments
• Also look OUTSIDE of your own subject
• Google Scholar
• Use advanced searching tools (don’t ignore book chapters)
• Use Web of Knowledge Citation Index with best articles
• Go 360° with citing articles, article references and related
records.
• WorldCat
• Rare items that are held by a few libraries – semi-published

7. Unpublished data
• Most valuable of all due to publication bias and the file drawer
problem
• Negative or null results less likely to have been published
resulting in skewed effect size in the population of published
studies

8. Finding unpublished data
• Dissertations
• Dissertations and Theses Full Text
• EThOS, Scirus, DART
• Conference proceedings
• Gray Literature
• Author websites (and email)
• Trial registries and regulatory agencies
• World Health Organization, FDA
• http://www.bmj.com/content/344/bmj.d8013
• Institutional repositories
• http://www.arl.org/sparc/repositories/collectedrep.shtml

9. The library is your friend
• Don’t hesitate to ask your subject librarian and interlibrary
loan for help – we like this stuff or we wouldn’t be doing it for
a living.