Even cash rewards may not motivate obese people to lose much weight, reports a new Cornell study.

When two Cornell researchers examined the effects of a yearlong program that offered cold cash for pounds lost, the majority of the obese volunteers in the study dropped out within the year. The average weight loss of those who stayed in the program, meanwhile, was only three to five pounds higher than that of a control group.

The findings are published as a working paper issued by the National Bureau of Economic Research.

John Cawley, associate professor of policy analysis and management in the College of Human Ecology, and graduate student Joshua A. Price evaluated data on 2,407 obese employees who participated in worksite health-promotion programs with their company in 17 locations. One group of workers received quarterly rewards for weight loss; another group paid a monthly fee that was refunded if they achieved weight loss goals. A third group that had no financial incentives served as the control group.

"After one year, those who were paid quarterly rewards lost an average of 1.4 pounds, which was not significantly different than the control group," said Cawley.

Those who paid the monthly refundable fees lost an average of 3.6 pounds -- 1.9 pounds more than the control group. However, "to some extent this may be due to only the most motivated workers being willing to pay monthly fees to participate," said Cawley, adding that these volunteers were less likely to drop out of the program. Their dropout rate was 57 percent compared with 76 percent in the group that was paid quarterly cash rewards. These drop-out rates, the authors report, were "far higher" than those reported in previous studies that were based on convenience samples instead of actual workplaces.

Obesity rates in the United States have doubled since 1980; as of 2003-04, 66 percent of

Americans were overweight and almost half of those were obese. Obesity is associated with a host of adverse health and labor market outcomes, Cawley said, so it is in employers' interests to help their obese employees lose weight.

The authors said that their findings were dependent on the magnitude of the financial rewards offered for weight loss. For example, an obese person who lost 5 percent of baseline weight received $15, but $75 for losing 20 percent. Cawley said that future work should test whether weight loss is greater when the financial rewards are higher.

Financial rewards for weight loss appear to hold some promise, he concluded, but it remains to be seen whether they can be as effective as the traditional medical approaches of pharmacologic and surgical therapy.

The study was supported in part by the Economic Research Service of the U.S. Department of Agriculture.