An observational study showed that explaining randomization using gambling-related metaphors and computer-agency descriptions impeded RCT recruitment.

To explore how the concept of randomisation is described by clinicians and understood by patients in randomised clinical trials (RCTs), and how it contributes to patient understanding and recruitment.Qualitative analysis of seventy-three audio recordings of recruitment consultations from five, multi-centre, UK based RCTs with identified or anticipated recruitment difficulties.One in ten appointments did not include any mention of randomisation. Most included a description of the method or process of allocation. Descriptions often drew on gambling-related metaphors or similies, or referred to allocation by a computer. Where reference was made to a computer, some patients assumed that they would receive the treatment that was 'best for them'. Descriptions of the rationale for randomisation were rarely present, and often only came about as a consequence of patients questioning the reason for a random allocation.The methods and processes of randomisation were usually described by recruiters, but often without clarity, which could lead to patient misunderstanding. The rationale for randomisation was rarely mentioned. Recruiters should avoid problematic gambling metaphors and illusions of agency in their explanations, and instead focus on clearer descriptions of the rationale and method of randomisation to ensure patients are better informed about randomisation and RCT participation.