The Cochrane Methodology Register (CMR) is a bibliography of publications that report on methods used in the conduct of controlled trials. It includes journal articles, books, and conference proceedings, and the content is sourced from MEDLINE and hand searches. CMR contains studies of methods used in reviews and more general methodological studies that could be relevant to anyone preparing systematic reviews. CMR records contain the title of the article, information on where it was published (bibliographic details), and, in some cases, a summary of the article. They do not contain the full text of the article.
The CMR was produced by the Cochrane UK, until 31st May 2012. There are currently no plans to reinstate the CMR and it is not receiving updates.* If you have any queries, please contact the Cochrane Community Service Team (support@cochrane.org).
The Publishers, John Wiley & Sons Ltd, thanks Update Software for the continued use of their data formats in the Cochrane Methodology Register (CMR).
*Last update in January 2019.
| Title | Simpson's paradox and calculation of number needed to treat from meta-analysis |
| Authors | Cates CJ |
| Source | BMC Medical Research Methodology |
| Date of publication | 2002 |
| Volume | 2 |
| Issue | 1 |
| Pages | 1 |
| 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. http://www.biomedcentral.com/content/pdf/1471-2288-2-1.pdf. |
| CMR keywords | CMR: Review methodolgy - meta-analysis - general;CMR: Review methodology - presentation of reviews - risk communication;CMRA4 |
| Correspondence address | Manor View Surgery, Bushey Health Centre, London Road, Bushey, Watford, UK. chriscates@email.msn.com |
| Reference type | Journal article |