Letter to the editor: Meta-analysis cannot count the same study six times: Why independence of studies is the first principle of evidence synthesis
Topic overview
This letter addresses a critical methodological error in meta-analysis: counting the same study multiple times. When studies lack independence, pooled estimates become artificially precise with falsely narrow confidence intervals, undermining the validity of evidence synthesis and clinical decision-making.
Key takeaways
- Meta-analysis requires each study to contribute independent evidence; duplicating studies violates this foundational principle.
- Including the same study multiple times artificially narrows confidence intervals and creates false precision in pooled estimates.
- Meta-analytic models assume distinct sampling error per study; duplication inflates weight and distorts statistical inference.
- Independence of studies is the first principle of evidence synthesis—without it, meta-analysis results become unreliable.
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How to cite: GlobalCastMD. Letter to the editor: Meta-analysis cannot count the same study six times: Why independence of studies is the first principle of evidence synthesis. GlobalCastMD Medical Library. 2025-09-08. https://library.globalcastmd.com/article/10960
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