Sample size requirements for pilot randomised controlled trials with binary outcomes: a simulation study

Aims There is lack of consensus over what sample size should be used for pilot trials to inform the design of definitive randomised controlled trials. The majority of the existing recommendations focus on estimating the variation of a continuous outcome and relatively little attention is paid to binary outcomes. The aim of this research was to investigate the sample size required to precisely estimate parameters such as event, consent and attrition rates. We assume that the pilot study (and the definitive RCT) will be a two parallel group treatment versus control design.