ArticleBMC medical research methodology2002
Simpson's paradox and calculation of number needed to treat from meta-analysis.
Article in BMC medical research methodology, 2002. The graph could read no effect estimate from its abstract, so it casts no vote on the map. Cited by 55 papers, 36 of them syntheses that pooled it.
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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.
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Who cites it
55 citing papers in PubMed, 36 syntheses or guidelines pooled it.
- Interventions for helping people recognise early signs of recurrence in bipolar disorder.The Cochrane database of systematic reviews · 2025Pooled it
- Peripheral nerve blocks for hip fractures in adults.The Cochrane database of systematic reviews · 2020Pooled it
- Mucolytic agents versus placebo for chronic bronchitis or chronic obstructive pulmonary disease.The Cochrane database of systematic reviews · 2019Pooled it
- The use of ultrasound guidance for perioperative neuraxial and peripheral nerve blocks in children.The Cochrane database of systematic reviews · 2019Pooled it
- Psychological therapies for anxiety and depression in children and adolescents with long-term physical conditions.The Cochrane database of systematic reviews · 2018Pooled it
- Patent foramen ovale closure versus medical therapy for prevention of recurrent cryptogenic embolism: updated meta-analysis of randomized clinical trials.Clinical research in cardiology : official journal of the German Cardiac Society · 2018Pooled it
- E-Health interventions for anxiety and depression in children and adolescents with long-term physical conditions.The Cochrane database of systematic reviews · 2018Pooled it
- Early life vitamin D status and asthma and wheeze: a systematic review and meta-analysis.BMC pulmonary medicine · 2018Pooled it
- Percutaneous closure versus medical therapy for stroke with patent foramen Ovale: a systematic review and meta-analysis.BMC cardiovascular disorders · 2018Pooled it
- Bayesian Analysis: A Practical Approach to Interpret Clinical Trials and Create Clinical Practice Guidelines.Circulation. Cardiovascular quality and outcomes · 2017Pooled it
- Peripheral nerve blocks for hip fractures.The Cochrane database of systematic reviews · 2017Pooled it
- Psychosocial interventions for supporting women to stop smoking in pregnancy.The Cochrane database of systematic reviews · 2017Pooled it
- Sequential versus standard triple first-line therapy for Helicobacter pylori eradication.The Cochrane database of systematic reviews · 2016Pooled it
- Bias and precision of methods for estimating the difference in restricted mean survival time from an individual patient data meta-analysis.BMC medical research methodology · 2016Pooled it
- The use of ultrasound guidance for perioperative neuraxial and peripheral nerve blocks in children.The Cochrane database of systematic reviews · 2016Pooled it
- Sub-Tenon's anaesthesia versus topical anaesthesia for cataract surgery.The Cochrane database of systematic reviews · 2015Pooled it
- Statins and Cardiovascular Primary Prevention in CKD: A Meta-Analysis.Clinical journal of the American Society of Nephrology : CJASN · 2015 · on this mapPooled it
- Common harms from amoxicillin: a systematic review and meta-analysis of randomized placebo-controlled trials for any indication.CMAJ : Canadian Medical Association journal = journal de l'Association medicale canadienne · 2015Pooled it
- Addition to inhaled corticosteroids of long-acting beta2-agonists versus anti-leukotrienes for chronic asthma.The Cochrane database of systematic reviews · 2014Pooled it
- Pooled it
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No grant is acknowledged in the PubMed record.
Abstract
backgroundCalculation 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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