Reporting number needed to treat and absolute risk reduction in randomized controlled trials

Abstract

Context: Ongoing efforts to improve the quality of reporting for randomized controlled trials (RCTs) include the Consolidated Standards of Reporting Trials (CONSORT) statement. We examined the frequency of explicit reporting of the number needed to treat (NNT) and the absolute risk reduction (ARR) in RCTs.

Methods: Five frequently cited journals were investigated: Annals of Internal Medicine, BMJ, JAMA, The Lancet, and the New England Journal of Medicine. For each journal, 4 years were evaluated: 1989, 1992, 1995, and 1998. All issues of each journal for each year were reviewed manually. Eligible articles were those in which an RCT was conducted on the use of a medication showing a significant treatment effect. Elements abstracted from each eligible article were the condition investigated, event being treated or prevented, intervention, study results, and reporting methods (relative risk reduction, NNT, and ARR).

Results: Of 359 eligible articles, NNT was reported in 8 articles. Six of the 8 studies were from 1998. Absolute risk reduction was reported in 18 articles, 10 of which were from 1998.

Conclusions: Despite CONSORT recommendations, few authors expressed their findings in terms of NNT or ARR. Consideration should be given to including these values in reports of RCTs.