Evidence map›Paper›PMID 9310563›Full record

ArticleBMJ (Clinical research ed.)1997

Bias in meta-analysis detected by a simple, graphical test.

M Egger, G Davey Smith, M Schneider, C Minder

3 registry-linked trialsAbstract read
PubMed Full text at PMC Publisher
In one paragraph

Article in BMJ (Clinical research ed.), 1997. The graph could read no effect estimate from its abstract, so it casts no vote on the map. It is linked to 3 registered trials, which are not on this map. Cited by 24,587 papers, 123 of them syntheses that pooled it.

0numbers the graph read from it
0cells of the map it votes in
24,587citing papers in PubMed, 123 pooled it
–field-weighted citation impact
1 · What the graph read from it

What it found

Each row is one number read from the abstract, on the scale the paper reported it, with its interval. Left of the dashed line favours the treatment, right favours the comparator. Under each row is the sentence it came from. New to these charts? A ten-minute tutorial.

The abstract states no effect estimate the extractor could read, or names no intervention and outcome on the map, so this paper lights no cell and moves no belief. It is still indexed, cited and linked below.

2 · The registry

The trial behind it

Trials whose registry record cites this paper, or whose number appears in the abstract. A trial that started after this paper was published is citing it as background, not reporting it.

NCT03234101 unknown statusnot on this mapstarted 2016, after this paper: background citation

Relation of Low-risk Lifestyle Behaviours With Cardiovascular Disease, Diabetes, Cancer and All-Cause Mortality: A Series of Systematic Reviews and Meta-analyses of Prospective Cohort Studies

TypeobservationalSponsorUniversity of TorontoRan2016 to 2017Enrolled1ConditionsCardiovascular Disease, Diabetes, Cancer, MortalityArmsLow-risk lifestyle behaviours
NCT04477941 completednot on this mapstarted 2020, after this paper: background citation

The Association Between Parents' Stress and Feeding Styles and Practices: Systematic Review and Meta-analysis of Observational Studies

TypeobservationalSponsorMathilda VandenheuvelRan2020 to 2022Enrolled1ConditionsParent-Child Relations, Stress, Feeding Behavior
NCT06951308 narecruitingnot on this mapstarted 2025, after this paper: background citation

Efficacy of Carbohydrate Loading in Diabetic Type 2 Patients Undergoing CABG Surgery on CPB

TypeinterventionalSponsorDamascus UniversityRan2025 to 2026Enrolled50ConditionsHeart Surgery, Ischemic Heart DiseaseArmsCarbohydrate loading before surgery
3 · Its place in the literature

Who cites it

24,587 citing papers in PubMed, 123 syntheses or guidelines pooled it.

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  5. Effects of acute Capsaicin analogue intake on athletic performance: a three-level meta-analysis.Journal of the International Society of Sports Nutrition · 2026
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24,527 more citing papers are in PubMed but not listed here.

4 · The record

Corrections and comments

5 · Who and what money

Authors and funding

4 authors.

M EggerDepartment of Social Medicine, University of Bristol. m.egger@bristol.ac.uk
G Davey Smith
M Schneider
C Minder

Funding

No grant is acknowledged in the PubMed record.

6 · The paper itself

Abstract

objectiveFunnel plots (plots of effect estimates against sample size) may be useful to detect bias in meta-analyses that were later contradicted by large trials. We examined whether a simple test of asymmetry of funnel plots predicts discordance of results when meta-analyses are compared to large trials, and we assessed the prevalence of bias in published meta-analyses.

designMedline search to identify pairs consisting of a meta-analysis and a single large trial (concordance of results was assumed if effects were in the same direction and the meta-analytic estimate was within 30% of the trial); analysis of funnel plots from 37 meta-analyses identified from a hand search of four leading general medicine journals 1993-6 and 38 meta-analyses from the second 1996 issue of the Cochrane Database of Systematic Reviews.

main outcome measureDegree of funnel plot asymmetry as measured by the intercept from regression of standard normal deviates against precision.

resultsIn the eight pairs of meta-analysis and large trial that were identified (five from cardiovascular medicine, one from diabetic medicine, one from geriatric medicine, one from perinatal medicine) there were four concordant and four discordant pairs. In all cases discordance was due to meta-analyses showing larger effects. Funnel plot asymmetry was present in three out of four discordant pairs but in none of concordant pairs. In 14 (38%) journal meta-analyses and 5 (13%) Cochrane reviews, funnel plot asymmetry indicated that there was bias.

conclusionsA simple analysis of funnel plots provides a useful test for the likely presence of bias in meta-analyses, but as the capacity to detect bias will be limited when meta-analyses are based on a limited number of small trials the results from such analyses should be treated with considerable caution.

Indexed as

BiasMeta-Analysis as TopicRandomized Controlled Trials as TopicRegression AnalysisStatistics as TopicTreatment Outcome

Identifiers

PMID9310563
PMCPMC2127453

What OpenQuestion holds

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Registered trials

Read under generation 80e0d062 · epoch 390. Bibliography from PubMed, PubMed Central and OpenAlex; grants from NIH RePORTER; trial links from ClinicalTrials.gov; estimates, votes and beliefs from the OpenQuestion graph.