Paying patients to participate in clinical trials is ethically controversial. However, there has been no empirical documentation regarding whether payment represents an undue or unjust inducement.
To evaluate these questions, we described hypothetical placebo-controlled trials of a new antihypertensive drug to 126 patients with mild-to-moderate hypertension recruited from hypertension and general medicine clinics at a university hospital. Using a 3 × 3, within-subjects design, we altered a risk to participation (either adverse effect rate or rate of randomization to placebo) and the payment participants would receive ($100, $1000, and $2000) and asked patients to indicate their willingness to participate (WTP) in each trial using a 6-point scale.
Clustered ordinal logistic regression models revealed that patients' WTP decreased with higher risk of adverse effects (P<.001), higher risk of being assigned to placebo (P = .02), and lower payment level (P<.001). There were no significant interactions between payment level and either risk variable, suggesting that increasing payments do not alter peoples' perceptions of risk. There was a trend toward a positive interaction between income and the influence of payment on WTP (P = .09), suggesting that payment more strongly influences WTP among wealthier people. Wealthier patients were more likely to state that payment was important in their participation decision (37% vs 20%, P = .05).
Although higher payment motivates research participation, we found no evidence that commonly used payment levels represent undue or unjust inducements.