Cook, Jonathan A., Julious, Stephen A., Sones, William, Hampson, Lisa V., Hewitt, Catherine, Berlin, Jesse A., Ashby, Deborah, Emsley, Richard, Fergusson, Dean A., Walters, Stephen J., Wilson, Edward C.F., McLennan, Graeme, Stallard, Nigel, Rothwell, Joanne C., Bland, Martin, Brown, Louise, Ramsay, Craig R., Cook, Andrew, Armstrong, David, Altman, Doug and Vale, Luke D. (2018) DELTA2 guidance on choosing the target difference and undertaking and reporting the sample size calculation for a randomised controlled trial. BMJ, [363]. (doi:10.1136/bmj.k3750).
Abstract
The randomised controlled trial (RCT) is considered the gold standard to assess comparative clinical efficacy and effectiveness and can be a key source of data for estimating cost- effectiveness. Central to the design of a RCT is an a-priori sample size calculation which ensures the study has a high probability of achieving its pre-specified main objective. Beyond pure statistical or scientific concerns, it is ethically imperative that an appropriate number of study participants be recruited, to avoid imposing the burdens of a clinical trial on more patients than necessary. The scientific concern is satisfied and the ethical imperative further addressed by specifying a target difference between treatments that is considered realistic and/or important by one or more key stakeholder groups. The sample size calculation ensures that the trial will have the required statistical power to identify whether a difference of a particular magnitude exists. The key messages from the DELTA2 guidance on determining the target difference and sample size calculation for a RCT are presented. Recommendations for the subsequent reporting of the sample size calculation are also provided.
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