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Cited by 251Meta-analysis and systematic reviewsStatistical Methods in Clinical TrialsStatistical Methods in Epidemiology

The DOI matches its Crossref record; 18 of the 18 references it cites were found in a registry or an index.

Simpson's paradox and calculation of number needed to treat from meta-analysis

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Cates, Christopher J·2002·BMC Medical Research Methodology
DOI 10.1186/1471-2288-2-1PMC PMC65632
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Abstract

BACKGROUND: Calculation of numbers needed to treat (NNT) is more complex from meta-analysis than from single trials. Treating the data as if it all came from one trial may lead to misleading results when the trial arms are imbalanced. DISCUSSION: An example is shown from a published Cochrane review in which the benefit of nursing intervention for smoking cessation is shown by formal meta-analysis of the individual trial results. However if these patients were added together as if they all came from one trial the direction of the effect appears to be reversed (due to Simpson's paradox). Whilst NNT from meta-analysis can be calculated from pooled Risk Differences, this is unlikely to be a stable method unless the event rates in the control groups are very similar. Since in practice event rates vary considerably, the use a relative measure, such as Odds Ratio or Relative Risk is advocated. These can be applied to different levels of baseline risk to generate a risk specific NNT for the treatment. SUMMARY: The method used to calculate NNT from meta-analysis should be clearly stated, and adding the patients from separate trials as if they all came from one trial should be avoided.

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  1. Senn S: At Odds with reality. BMJ Rapid Response. [http://www.bmj.com/cgi/eletters/318/7197/1548#EL2]

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Metadata

Authors
Cates, C. J.
Corresponding author
Cates, Christopher J
ORCID
Cates, Christopher J
Venue
BMC Medical Research Methodology
Publisher
Springer Science and Business Media LLC
Published
2002-01-25
Volume
2
Issue
1
Pages
1-1
ISSN
1471-2288 (ISSN-L)
DOI
10.1186/1471-2288-2-1
PMC
PMC65632
OpenAlex
W1576173198
Cited by
251
References
17
Citations by year
2026: 2 · 2025: 4 · 2024: 7 · 2023: 3 · 2022: 3 · 2021: 20 · 2020: 13 · 2019: 14 · 2018: 16 · 2017: 22 · 2016: 23 · 2015: 8 · 2014: 13 · 2013: 13 · 2012: 10
FWCI
10.16
Type
journal article
Language
en
Open access
Licence
www.springer.com/tdm (unspecified)
Locations
  • BMC Medical Research Methodology (publishedVersion)
  • Europe PMC (PubMed Central) (publishedVersion, other-oa)
  • PubMed Central (publishedVersion, other-oa)
  • PubMed (publishedVersion)
  • St George's Online Research Archive (St George's University of London) (acceptedVersion)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion)
Topics
  • Social Sciences › Decision Sciences › Statistics, Probability and Uncertainty › Meta-analysis and systematic reviews
  • Physical Sciences › Mathematics › Statistics and Probability › Statistical Methods in Clinical Trials
  • Physical Sciences › Mathematics › Statistics and Probability › Statistical Methods in Epidemiology
Keywords
Simpson's paradox, number needed to treat, meta-analysis, risk difference, odds ratio, relative risk, baseline risk, smoking cessation, nursing interventions
MeSH terms
Clinical Trials as Topic, Data Interpretation, Statistical, Humans, Statistics as Topic, Meta-Analysis as Topic, Reproducibility of Results, Bias, Odds Ratio, Smoking Cessation, Sample Size

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