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Financial Incentives for Research Participation: Empirical Questions, Available Answers and the Burden of Further Proof

The growing gap between the supply of and demand for clinical research participants has motivated efforts to better understand how people make decisions to participate in research and specifically what investigators ethically can do to improve study enrollment. Among the several reasons why potential research subjects would or would not participate in studies, the opportunity for financial compensation or benefit often figures prominently among both patients1 and healthy volunteers (Stunkel and Grady, “More than the money: a review of the literature examining healthy volunteer motivations,” unpublished). Common sense, anecdotal experiences and the few empirical analyses conducted to date all suggest that financial incentives are effective ways to increase study enrollment and that larger incentives are more effective than are smaller ones.2,3 Although financial incentives for research participation are common,4 the practice remains controversial. Unfortunately, commentators on the ethics of incentives for research have been united far more by the fervor of their arguments than by the underlying concepts on which the arguments are based. In this essay, I attempt to bring clarity to the debate by (1) distinguishing the legitimate from the illegitimate concerns with financial incentives for human research participation; (2) reviewing the available data that substantiate or repudiate the legitimate concerns and (3) considering the flip-side of the coin: the potential ethical merits of financial incentives. I conclude that although the current evidence base on incentives for research participation is suboptimal, the available data call into question each of the otherwise legitimate concerns with payment. In light of these findings and the fact that restrictions on financial incentives carry ethical problems of their own, I suggest that unless or until compelling evidence emerges to substantiate concerns with payment, financial incentives should be viewed as reasonable and ethical approaches to motivate research participation.