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A meta-analysis is defined by Haidlich (2010) as "quantitative, formal, epidemiological study design used to systematically assess previous research studies to derive conclusions about that body of research. Outcomes from a meta-analysis may include a more precise estimate of the effect of treatment or risk factor for disease, or other outcomes, than any individual study contributing to the pooled analysis" (p.29).
According to Grant & Booth (2009), a meta-analysis is defined as a "technique that statistically combines the results of quantitative studies to provide a more precise effect of the results" (p.94).
Characteristics
When to Use It: According to the Cochrane Handbook, "an important step in a systematic review is the thoughtful consideration of whether it is appropriate to combine the numerical results of all, or perhaps some, of the studies. Such a meta-analysis yields an overall statistic (together with its confidence interval) that summarizes the effectiveness of an experimental intervention compared with a comparator intervention" (section 10.2).
Conducting meta-analyses can have the following benefits, according to Deeks et al. (2021, section 10.2):
The following resource provides further support on conducting a meta-analysis.
Methods & Guidance
A comprehensive overview on meta-analyses within the Cochrane Handbook.
Reporting Guideline
PRISMA (2020) is a 27-item checklist that replaces the PRISMA (2009) statement, which ensures proper and transparent reporting for each element in a systematic review and meta-analysis. "It is an expanded checklist that details reporting recommendations for each item, the PRISMA 2020 abstract checklist, and the revised flow diagrams for original and updated reviews."
Deeks, J.J., Higgins, J.P.T., & Altman, D.G. (Eds.). (2021). Chapter 10: Analysing data and undertaking meta-analyses. In Higgins, J.P.T., Thomas J., Chandler, J., Cumpston, M., Li, T., Page, M.J., & Welch, V.A. (Eds.), Cochrane Handbook for Systematic Reviews of Interventions version 6.2. Cochrane. Available from www.training.cochrane.org/handbook
Grant, M. J., & Booth, A. (2009). A typology of reviews: an analysis of 14 review types and associated methodologies. Health information and libraries journal, 26(2), 91–108. doi: 10.1111/j.1471-1842.2009.00848.x
Haidich A. B. (2010). Meta-analysis in medical research. Hippokratia, 14(Suppl 1), 29–37.
Seidler, A.L., Hunter, K.E., Cheyne, S., Ghersi, D., Berlin, J.A., & Askie, L. (2019). A guide to prospective meta-analysis. BMJ, 367, l5342. doi: 10.1136/bmj.l5342
The following challenges of conducting meta-analyses in systematic reviews are derived from Grant & Booth (2009), Haidlich (2010), and Deeks et al. (2021).