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Related Experiment Videos

Publication bias and meta-analyses: a practical example.

Sarah Burdett1, Lesley A Stewart, Jayne F Tierney

  • 1Meta-analysis Group, Medical Research Council Clinical Trials Unit, London, UK. sb@ctu.mrc.ac.uk

International Journal of Technology Assessment in Health Care
|April 19, 2003
PubMed
Summary
This summary is machine-generated.

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Including gray+ literature in systematic reviews, such as unpublished or non-English randomized controlled trials (RCTs), can alter results. Adding this data often leads to less favorable treatment effects, moving them toward a null result.

Area of Science:

  • Medical research methodology
  • Evidence-based medicine
  • Systematic review best practices

Background:

  • Publication bias is a known issue in systematic reviews.
  • Locating unpublished or non-English randomized controlled trials (RCTs) is time-consuming.
  • Excluding gray+ literature may introduce bias into systematic reviews.

Purpose of the Study:

  • To quantify the impact of including gray+ literature on systematic review results.
  • To compare meta-analyses using only English publications versus those including gray+ literature.

Main Methods:

  • Utilized individual patient data (IPD) from 13 meta-analyses coordinated by the group.
  • Calculated review results using English-language RCTs only.
  • Calculated review results using English-language RCTs plus gray+ literature.

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Main Results:

  • Meta-analyses including gray+ literature generally showed less favorable results.
  • The inclusion of gray+ data often shifted estimated treatment effects toward a null result.
  • The direction of the effect modification by gray+ literature was not always predictable.

Conclusions:

  • Systematic reviews should strive to identify and include gray+ literature.
  • Obtaining data from gray+ literature, where feasible, is recommended to minimize bias.