The researchers studied two types of incentive strategies: a group incentive and an individual one. In the individual approach, employees were offered $100 for each month they met or exceeded weight-loss goals. For the other, groups of five employees were offered $500 a month to be divided equally among only the members who met their goals. Those who didn't meet their goals received no money. The five-member groups had no way of learning each other's identities, so they couldn't intentionally tempt or discourage each other in an effort to personally win a bigger share of the pie.
The potential upfront cost to an employer was the same for either strategy. A control group was created to compare the two strategies to one in which people had no financial incentive. Those participants got a link to a national weight-control website, along with monthly weigh-ins supported by email or text reminders.
After 24 weeks, participants in the group-incentive plan lost about 7 pounds more on average than those who were in the individual plan, and an average of almost 10 pounds more than those in the control group. Twelve weeks after the program ended, those in the group incentive plan maintained more weight loss than those in the control group, but not more than those in the individual incentive plan.
What is the psychology behind the study results? Price matters, said Jason Riis, who wrote an editorial accompanying the research. "Some amount of money constantly at stake each month -- a goal and a reward -- does seem to be a mechanism to help people make slightly better decisions," said Riis, an assistant professor of business administration at Harvard Business School.
For those who don't have access to employer-based programs, Riis suggested people create incentives between themselves and friends. He recommended Stickk.com, created by a Yale University economics professor who came up with the idea of opening an online "commitment store."
Participants sign contracts obliging them to achieve their personal goals, such as losing weight, with the risk of a financial penalty if they fail.
Whatever the approach, the key to maintaining weight loss over the long term remains elusive, Riis said. "We're a long way from knowing the answers to that," he said.