Evidence map›Paper›PMID 19216779›Full record

ReviewBMC medical research methodology2009

Overstating the evidence: double counting in meta-analysis and related problems.

Stephen J Senn

Abstract readReview
PubMed Full text at PMC Publisher
In one paragraph

Review in BMC medical research methodology, 2009. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 84 papers, 51 of them syntheses that pooled it.

0numbers the graph read from it
0cells of the map it votes in
84citing papers in PubMed, 51 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.

Neither the registry nor the abstract names a trial number. If this is a trial report, that itself is worth knowing.

3 · Its place in the literature

Who cites it

84 citing papers in PubMed, 51 syntheses or guidelines pooled it.

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  13. Lung Cancer Risk in US Adults with COPD: A Systematic Review and Meta-Analysis.International journal of chronic obstructive pulmonary disease · 2025
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24 more citing papers are in PubMed but not listed here.

4 · The record

Corrections and comments

PubMed lists nothing against this paper. Absence here is not a guarantee, only a check that was made.

5 · Who and what money

Authors and funding

1 author.

Stephen J SennDepartment of Statistics, University of Glasgow, Glasgow, UK. stephen@stats.gla.ac.uk

Funding

No grant is acknowledged in the PubMed record.

6 · The paper itself

Abstract

backgroundThe problem of missing studies in meta-analysis has received much attention. Less attention has been paid to the more serious problem of double counting of evidence.

methodsVarious problems in overstating the precision of results from meta-analyses are described and illustrated with examples, including papers from leading medical journals. These problems include, but are not limited to, simple double counting of the same studies, double counting of some aspects of the studies, inappropriate imputation of results, and assigning spurious precision to individual studies.

resultsSome suggestions are made as to how the quality and reliability of meta-analysis can be improved. It is proposed that the key to quality in meta-analysis lies in the results being transparent and checkable.

conclusionExisting quality check lists for meta-analysis do little to encourage an appropriate attitude to combining evidence and to statistical analysis. Journals and other relevant organisations should encourage authors to make data available and make methods explicit. They should also act promptly to withdraw meta-analyses when mistakes are found.

Indexed as

Data Interpretation, StatisticalMeta-Analysis as TopicClinical Trials as TopicHumansMethodsRandomized Controlled Trials as TopicReview Literature as Topic

Identifiers

PMID19216779
PMCPMC2653069

What OpenQuestion holds

Textmetadata
LicenceCC BY
Read underepoch 390

Registered trials

None linked

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.