Cited by 7,709Meta-analysis and systematic reviewsStatistical Methods in EpidemiologyStatistical Methods in Clinical Trials

Recommendations for examining and interpreting funnel plot asymmetry in meta-analyses of randomised controlled trials

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Sterne, J. A. C., Sutton, A. J., Ioannidis, J. P. A., Terrin, N., Jones, D. R., Lau, J., Carpenter, J., Rucker, G. +11 more·2011·BMJ

Abstract

Funnel plots, and tests for funnel plot asymmetry, have been widely used to examine bias in the results of meta-analyses. Funnel plot asymmetry should not be equated with publication bias, because it has a number of other possible causes. This article describes how to interpret funnel plot asymmetry, recommends appropriate tests, and explains the implications for choice of meta-analysis model

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  • The non-significant tendencies to asymmetry and small study effects identified by the Eggers and Begg tests, presumably caused by the similar SEM of most of the studies, can be assumed to be trustworthy.

    “so the non-significant tendencies to asymmetry and small study effects identified by the Eggers and Begg tests, presumably caused by the similar SEM of most of the studies, can be assumed to be trustworthy [30].”

    From Are Dietary Proteins the Key to Successful Body Weight Management? A Systematic Review and Meta-Analysis of Studies Assessing Body Weight Outcomes after Interventions with Increased Dietary Protein (2021) · cites this paper as [30]

    Box 2 says asymmetry tests should not be used when studies’ standard errors are all similar. The Statistical tests for funnel plot asymmetry section also says these tests have low power and that a non-significant result cannot exclude bias. The paper therefore does not support treating the reported test results as trustworthy because the studies had similar SEMs. (LLM, conf=0.90)

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  • Publication bias was not assessed because no forest plot had at least ten studies.

    “publication bias was not assessed in this review because there was no forest plot with at least ten studies (Sterne et al. 2011).”

    From The Effect of Mindfulness-Based and Acceptance Commitment Therapy-Based Interventions to Improve the Mental Well-Being Among Parents of Children with Developmental Disabilities: A Systematic Review and Meta-Analysis. (2022) · cites this paper as Sterne et al. 2011

    Box 2 recommends against tests for funnel plot asymmetry when a meta-analysis has fewer than 10 studies, because such tests usually have too little power. It does not say that publication bias cannot be assessed by other means, and the citing review’s study counts are its own finding, not a finding of this source. (LLM, conf=0.86)

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  • Publication bias was assessed using funnel plot analysis and Egger's test where the number of studies for the outcome of interest was at least 10.

    “Publication bias was assessed using funnel plot analysis and Egger's test where the number of studies for the outcome of interest was ≥10”

    From IVF/ICSI or surgery as first approach for the treatment of infertility associated with ovarian and deep infiltrating endometriosis? A systematic review and meta-analysis. (2026) · cites this paper as Sterne et al., 2011

    Box 2 recommends against tests for funnel-plot asymmetry with fewer than 10 studies and says Egger’s test may be used for continuous outcomes. It also cautions that some analyses need more than 10 studies, that other tests may be preferable for dichotomous outcomes, and that asymmetry does not necessarily indicate publication bias. The source supports the cited threshold as a rule of thumb, not as a sufficient condition for using Egger’s test to assess publication bias in every outcome. (LLM, conf=0.85)

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  • Publication bias was assessed by visual inspection of funnel plot asymmetry for comparisons with data from at least ten studies.

    “For those comparisons in which data were obtained from at least ten studies (Sterne et al. 2011), publication bias was assessed by visual inspection of funnel plot asymmetry.”

    From Analysis of sex-based differences in energy substrate utilization during moderate-intensity aerobic exercise (2022) · cites this paper as Sterne et al. 2011

    Box 2 recommends avoiding statistical tests for funnel plot asymmetry when a meta-analysis has fewer than ten studies and says test results should be interpreted alongside visual inspection. It does not set ten studies as a threshold specifically for visual inspection. Box 2 also cautions that asymmetry has causes other than publication bias, so visual inspection alone cannot establish publication bias. (LLM, conf=0.88)

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  • The asymmetry likely represents a 'small study bias', where methodological approaches inherent in small studies lead to stronger effects with greater variance.

    “Instead, the asymmetry likely represents a ‘small study bias’, where methodological approaches inherent in small studies lead to stronger effects with greater variance (Peters et al., 2008; Sterne et al., 2011).”

    From The Distributed Practice Effect on Classroom Learning: A Meta-Analytic Review of Applied Research (2025) · cites this paper as Sterne et al., 2011

    The Heterogeneity section (page not specified in our copy) says smaller studies tend to use less rigorous methods and that lower-quality trials tend to show larger effects. The Reporting bias section says smaller studies have more sampling error. But the Discussion describes multiple possible causes of funnel plot asymmetry; the paper does not establish that methodological bias is the likely cause of the particular asymmetry described here. (LLM, conf=0.86)

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Authors
Sterne, J. A. C., Sutton, A. J., Ioannidis, J. P. A., Terrin, N., Jones, D. R., Lau, J., Carpenter, J., Rucker, G., Harbord, R. M., Schmid, C. H., Tetzlaff, J., Deeks, J. J., Peters, J., Macaskill, P., Schwarzer, G., Duval, S., Altman, D. G., Moher, D., & Higgins, J. P. T.
Affiliations
  • University of Bristol (GB)
  • University of Leicester (GB)
  • Stanford Medicine (US)
  • Tufts University (US)
  • London School of Hygiene & Tropical Medicine (GB)
  • Ottawa Hospital Research Institute (CA)
  • University of Birmingham (GB)
  • University of Exeter (GB)
  • The University of Sydney (AU)
  • University of Freiburg (DE)
  • University of Minnesota (US)
  • University of Oxford (GB)
Corresponding author
Sterne, J. A. C.
Venue
BMJ
Publisher
BMJ
Published
2011-07-22
Volume
343
Issue
jul22 1
Pages
d4002-d4002
ISSN
  • 0007-1447 (ISSN-L)
  • 0959-8138
  • 1468-5833
OpenAlex
W2119605658
Cited by
7,709
References
45
Citations by year
2026: 967 · 2025: 792 · 2024: 824 · 2023: 766 · 2022: 786 · 2021: 687 · 2020: 610 · 2019: 492 · 2018: 447 · 2017: 377 · 2016: 304 · 2015: 241 · 2014: 197 · 2013: 122 · 2012: 74
FWCI
136.80
Type
journal article
Language
en
Open access
Locations
  • BMJ (publishedVersion)
  • PubMed (publishedVersion)
  • Bristol Research (University of Bristol) (publishedVersion)
  • LSHTM Research Online (London School of Hygiene and Tropical Medicine) (acceptedVersion)
  • Leicester Research Archive (University of Leicester) (submittedVersion)
  • HighWire Press Open Archive (submittedVersion)
  • University of Birmingham Research Portal (University of Birmingham) (submittedVersion)
  • Explore Bristol Research (submittedVersion)
Funders
  • Cancer Research UK
  • Deutsche Forschungsgemeinschaft (FOR 534)
  • Canadian Institutes of Health Research
  • Medical Research Council (U1052.00.011)
Topics
  • Social Sciences › Decision Sciences › Statistics, Probability and Uncertainty › Meta-analysis and systematic reviews
  • Physical Sciences › Mathematics › Statistics and Probability › Statistical Methods in Epidemiology
  • Physical Sciences › Mathematics › Statistics and Probability › Statistical Methods in Clinical Trials
Keywords
funnel plot asymmetry, publication bias, meta-analysis bias, randomized controlled trials, heterogeneity
MeSH terms
Statistics as Topic, Meta-Analysis as Topic, Selection Bias, Randomized Controlled Trials as Topic

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