Evidence map›Paper›PMID 18513392›Full record

ArticleBMC medical research methodology2008

Simpson's paradox visualized: the example of the rosiglitazone meta-analysis.

Gerta Rücker, Martin Schumacher

Abstract read
PubMed Full text at PMC Publisher
In one paragraph

Article in BMC medical research methodology, 2008. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 42 papers, 12 of them syntheses that pooled it.

0numbers the graph read from it
0cells of the map it votes in
42citing papers in PubMed, 12 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

42 citing papers in PubMed, 12 syntheses or guidelines pooled it.

  1. Changes in sex distribution in Achilles tendon rupture literature over 74 years: A systematic review.Knee surgery, sports traumatology, arthroscopy : official journal of the ESSKA · 2026
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  7. A Meta-analysis of Gut Microbiota in Children with Autism.Journal of autism and developmental disorders · 2022
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  18. What if 0 is not equal to 0? Inter-personal health utilities anchoring using the largest health gains.The European journal of health economics : HEPAC : health economics in prevention and care · 2023
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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

2 authors.

Gerta RückerInstitute of Medical Biometry and Medical Informatics, University Medical Center Freiburg, Germany. ruecker@imbi.uni-freiburg.de
Martin Schumacher

Funding

No grant is acknowledged in the PubMed record.

6 · The paper itself

Abstract

backgroundSimpson's paradox is sometimes referred to in the areas of epidemiology and clinical research. It can also be found in meta-analysis of randomized clinical trials. However, though readers are able to recalculate examples from hypothetical as well as real data, they may have problems to easily figure where it emerges from.

methodFirst, two kinds of plots are proposed to illustrate the phenomenon graphically, a scatter plot and a line graph. Subsequently, these can be overlaid, resulting in a overlay plot. The plots are applied to the recent large meta-analysis of adverse effects of rosiglitazone on myocardial infarction and to an example from the literature. A large set of meta-analyses is screened for further examples.

resultsAs noted earlier by others, occurrence of Simpson's paradox in the meta-analytic setting, if present, is associated with imbalance of treatment arm size. This is well illustrated by the proposed plots. The rosiglitazone meta-analysis shows an effect reversion if all trials are pooled. In a sample of 157 meta-analyses, nine showed an effect reversion after pooling, though non-significant in all cases.

conclusionThe plots give insight on how the imbalance of trial arm size works as a confounder, thus producing Simpson's paradox. Readers can see why meta-analytic methods must be used and what is wrong with simple pooling.

Indexed as

Data Interpretation, StatisticalMeta-Analysis as TopicChildElectric Power SuppliesHumansLeukemiaMyocardial InfarctionRandomized Controlled Trials as TopicRosiglitazoneSample SizeStatistics as TopicThiazolidinedionesRosiglitazoneThiazolidinediones

Identifiers

PMID18513392
PMCPMC2438436

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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.