DELTA² guidance on choosing the target difference and undertaking and reporting the sample size calculation for a randomised controlled trial

Central to the design of a randomised controlled trial is an a priori sample size calculation, which ensures a high probability of the study achieving its prespecified main objective An incorrect sample size can result in a study that is unable to inform clinical practice (hence directly or indirectly harming patients), or could expose excess patients to the uncertainty inherent in a clinical trial