Navigating the consent river: questions to consider before waiving consent requirements in pragmatic cluster randomised trials

The robust design and conduct of pragmatic cluster randomised trials may be in tension with the ethical requirement to obtain written informed consent from prospective research participants. In our experience, researchers tend to focus on whether a waiver of consent is appropriate for their studies. However, pragmatic cluster randomised trials raise other important questions that have direct implications for determining when an alteration or waiver of consent is permissible. To assist those involved in the design, conduct and review of pragmatic cluster randomised trials, we outline four critical questions to consider: (1) What is the nature of the intervention being evaluated? (2) Is the choice to use cluster randomisation justified? (3) Can the risk of recruitment bias be addressed? and (4) Is an alteration or waiver of consent appropriately justified? We recommend that researchers and research ethics committees conduct a stepwise analysis of a planned cluster randomised trial using these questions. To illustrate the application of this stepwise analysis, we use three pragmatic cluster randomised trials in the haemodialysis setting as case studies.