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Specifying the target difference in the primary outcome for a randomised controlled trial: guidance for researchers

2015; Springer Science+Business Media; Volume: 16; Issue: 1 Linguagem: Inglês

10.1186/s13063-014-0526-8

1745-6215

Jonathan Cook, Jenni Hislop, Douglas G. Altman, Peter Fayers, Andrew Briggs, Craig Ramsay, John Norrie, Ian Harvey, Brian S Buckley, Dean Fergusson, Ian Ford, Luke Vale,

Aortic aneurysm repair treatments

Central to the design of a randomised controlled trial is the calculation of the number of participants needed. This is typically achieved by specifying a target difference and calculating the corresponding sample size, which provides reassurance that the trial will have the required statistical power (at the planned statistical significance level) to identify whether a difference of a particular magnitude exists. Beyond pure statistical or scientific concerns, it is ethically imperative that an appropriate number of participants should be recruited. Despite the critical role of the target difference for the primary outcome in the design of randomised controlled trials, its determination has received surprisingly little attention. This article provides guidance on the specification of the target difference for the primary outcome in a sample size calculation for a two parallel group randomised controlled trial with a superiority question.