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Rating Down for Publication Bias is Rare in Cochrane Reviews: A Descriptive Study
Markus Toews1, Silvia Minozzi2, Bernardine H Stegeman3
1Institute for Evidence in Medicine, Medical Center-University of Freiburg, Faculty of Medicine University of Freiburg Freiburg Germany.
Cochrane Evidence Synthesis and Methods
|July 29, 2026
Summary
Publication bias is rarely rated down in Cochrane reviews, even though it is common in research. Guidance may be insufficient for reviews with fewer than 10 studies, impacting certainty of evidence assessments.
Area of Science:
- Systematic Reviews and Meta-Analysis
- Evidence-Based Medicine
- Research Integrity
Background:
- Publication bias significantly influences systematic review findings and confidence in conclusions.
- The extent to which publication bias is addressed in certainty of evidence assessments within systematic reviews is not well understood.
- This study examines the frequency of downgrading for publication bias in Cochrane reviews.
Purpose of the Study:
- To provide an overview of how often the GRADE (Grading of Recommendations, Assessment, Development and Evaluations) domain of publication bias leads to a rating down of evidence certainty.
- To estimate the prevalence of downgrading for publication bias across Cochrane reviews.
Main Methods:
- A descriptive study analyzing Cochrane reviews published between January 2021 and October 2023.
- Inclusion criteria: Cochrane reviews with at least one outcome rated down for publication bias.
- Data extraction from review texts, analyses, and figures; descriptive statistical analysis and deductive qualitative analysis.
Main Results:
- 81 Cochrane reviews were included, encompassing 1 to 328 studies each.
- Funnel plots were the most common method for detecting publication bias.
- 220 outcomes were downgraded by one level, and 4 by two levels for publication bias, often due to funnel plot indications.
Conclusions:
- Downgrading for publication bias was infrequent in the analyzed Cochrane reviews, contrasting with its prevalence in primary research.
- Existing guidance may be inadequate for assessing publication bias in systematic reviews based on fewer than 10 studies.
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