When it comes to offering to pay clinical trial subjects to participate, the line between compensation and coercion is difficult to draw but all too easy to cross.

Reimbursing participants for expenses incurred — travel, lodging, childcare — is a standard practice and clearly approved by the FDA. But the agency’s stand on incentive payments is not as clear, aside from a cautionary note in its Payment and Reimbursement to Research Subjects information sheet that advises IRBs to consider whether “proposed payment for participation could present an undue influence, thus interfering with the potential subjects’ ability to give voluntary informed consent.”

But one IRB expert says the consideration of influence as opposed to incentive should begin with the research team.

“Research teams have an obligation to implement an effective consent process, which includes ensuring that there are no undue inducements introduced into the process,” says David Borasky, vice president of IRB compliance for WIRB-Copernicus Group.

“When an IRB reviews a proposed study, it is only able to consider the population of potential subjects in the aggregate. The IRB cannot know how every potential participant might react to an incentive, and so it must approve research where the potential for an undue inducement has been minimized and rely on the research team to conduct an appropriate consent process.”

“I am not sure why it should be the IRB’s role to determine how individuals may want to use their time in order to receive a financial incentive, or why an IRB would believe it is in the best position to understand the impact at the level of the individual.”

Still, most IRBs are cautious about payments and may reject or reduce those that are “out of the norm.” The FDA advises IRBs to review both the amount of the incentive payment and the proposed method and timing of disbursement to assure that neither are coercive or present undue influence. For instance, payment should not be contingent on a participant’s completion of the trial. “Any credit for payment should accrue as the study progresses and not be contingent upon the subject completing the entire study,” the agency says.

But too much IRB involvement in setting payment amounts can hinder a trial. “There is nothing wrong with mere influence and demonstrating respect for persons by allowing individuals to decide for themselves,” Borasky says. “In fact, one could argue that if an IRB chooses to require a lower incentive, it is then making it impossible for a segment of the population to participate, because participation for some is not feasible without the presence of a financial incentive.”

“I don’t think there’s any doubt that lower-income individuals may be more attracted by a financial incentive compared to someone from a higher income bracket, but that does not mean it is automatically an undue influence,” he continued.

Paying for participation can also level the field among such disparate groups, says Susan Groth, associate professor at the University of Rochester School of Nursing.

“Use of financial incentives can enhance enrollment without undue coercion of any particular population and can serve as a means to equalize study participation,” says Groth, who served as a co-investigator on an NIH-funded study that explored the use of electronic technology to promote healthy pregnancies among women.

But the question of “reasonable” financial incentive can be challenging. Thinking in terms of risk in addition to time and effort, she explains, helps illustrate the difference between payment for services and compensation for a personal contribution. It’s important to demonstrate respect for what participants give — or give up — to take part in a clinical trial.