The ethical permissibility of financial incentives

Randomized controlled trials are central to progress in medicine, but trialists commonly struggle to recruit the required number of participants. Offering financial incentives is one proposed solution, but financial incentives may be problematic when they become irresistible and, thus, undermine the autonomy of potential participants. While some have dismissed this worry about undue inducement and argued that we should be paying participants more to avoid exploitation, we argue that this line of argument is based on a too narrow conception of undue inducement and does not fully appreciate the distinction between reimbursement, compensation, and financial incentives. On another, often overlooked concept of undue inducement, large incentives are an undue inducement when they are irresistible for people who do not want to participate and, thus, undermine voluntariness. This gives reason to limit the financial incentives to trial participants. We argue, furthermore, that large financial incentives could also be disproportionally attractive for people from economically marginalized groups and result in an unjust distribution of the burdens of research participation. We conclude that, while small sums of money are permissible as incentives, larger financial incentives should be avoided. We end by responding to the objection that keeping payments to participants small would be a form of exploitation. We argue that this argument does not apply to financial incentives. Unlike reimbursements and compensation, financial incentives are not payments to which participants can have a claim and, therefore, fall outside the scope of exploitation arguments.