Financial Incentives Can Be Effective in Increasing Clinical Trial Participation

By Linda Carroll

September 22, 2021

(Reuters Health) - Offering potential clinical trial participants money to sign up may be an effective way to boost enrollment, a new study suggests.

An analysis of data from two studies embedded in two larger ones also revealed that offering financial incentives did not appear to be more effective among poorer individuals than more wealthy ones, according to the results published in JAMA Internal Medicine.

"These two randomized trials provide the first real-world evidence regarding the effects of a very commonplace practice, that is, providing financial incentives to encourage participation, and the possibility that those incentives may be unethical," said the study's first author, Dr. Scott D. Halpern, John M. Eisenberg Professor of Medicine, Epidemiology, and Medical Ethics and Health Policy and director of the Palliative and Advanced Illness Research Center at the University of Pennsylvania Perelman School of Medicine in Philadelphia.

"In two separate real-world randomized trials, offers of several hundred dollars had variable effects on participation, substantially increasing enrollment rates in one and not budging them in the other," Dr. Halpern said. "In neither study did incentives show any evidence of yielding the two problems ethicists have long feared: the possibility that incentives would blind people to risk and thereby be undue inducement or the possibility that they may preferentially be influential among disadvantaged persons, namely those with lower incomes."

To take a closer look at the impact of financial incentives on enrollment in clinical trials, Dr. Halpern and his colleagues embedded their two experiments in two pre-existing "parent" trials that were recruiting participants: one comparing smoking cessation interventions and the other an evaluation of a gamification intervention to promote ambulation among hospitalized patients as compared with usual care.

The researchers included all persons who were eligible for the parent trials and did not tell the prospective participants about the incentives studies. Potential participants were recruited from September 2017 to August 2019 for the smoking trial and from January 2018 through May 2019 for the ambulation trial. Patients were randomly assigned to incentives of $0, $200 or $500 for participating in the smoking cessation trial and $0, $100 or $300 for the ambulation trial.

After patients made their choice to consent to participate in the parent trial or not, the researchers administered a questionnaire assessing how patients perceived the risks of participating in the parent trials, as measured by a modified version of the compared riskiness scale.

A total of 654 participants, of whom 327 (50.0%) were women, with a mean age of 50.6 years were in the smoking trial. Among these participants, 394 (60.2%) were Black/African American, 214 (32.7%) white, and 24 (3.7%) multiracial. A total of 642 participants were in the ambulation trial: 364 (56.7%) women, mean age 46.7 years, 224 (34.9%) Black/African American, 335 (52.2%) white, and five (0.8%) multiracial.

The financial incentives significantly increased consent rates among those in the smoking trial with 47 of 216 (21.8%) of those offered $0 enrolling, 78 of 217 (35.9%) of those offered $200 enrolling, and 104 of 221 (47.1%) of those offered $500 enrolling. That led to an adjusted odds ratio of 1.70 for each increase in incentive.

Incentives did not increase consent rates among those in the ambulation trial: 98 of 216 (45.4%), 102 of 212 (48.1%), and 92 of 214 (43.0%) in the $0, $100, and $300 incentive groups, respectively, signed up for the trial (aOR 0.88).

The researchers found no evidence in either trial of undue or unjust inducement. They also found no significant effects of incentives on perceived research risks, trial understanding, perceived coercion, or therapeutic misconceptions.

There is always a concern that the hunger for better results may cloud researchers' evaluation of the ethics of a study, said Robert Fullilove, a professor of sociomedical sciences and associate dean of community and minority affairs at the Columbia University Mailman School of Public Health in New York City.

It would have been helpful if the researchers had interviewed the participants and asked them how big of a role the financial incentive played in their decision to sign on for the study, Fullilove said. "Maybe one of the biggest weaknesses of the study is their making assumptions about the motives of those who accepted the incentive," he added. "It would have been interesting to talk to them rather than to speculate on what was in their minds when they made their decision."

SOURCE: and JAMA Internal Medicine, online September 20, 2021.