"[Behavioral economists Kevin Volpp of the University of Pennsylvania School of Medicine and the Wharton School and George Lowenstein of Carnegie Mellon University] designed a program in which a group of volunteers enrolled in a 16-week diet program with monthly weigh-ins and an overall goal of shedding 16 lb. The volunteers were then divided into three groups. The first group participated in a lottery program in which those who came closest to or exceeded the weight-loss goal received a variable cash prize determined by how many pounds they shed. The second group agreed to a deposit contract in which they anted up some of their own money as part of a pool. Those who lost the most weight split the pot; those who didn't drop enough weight lost their investment. The last group was given no financial incentive and relied on willpower and commitment alone. No surprise who did best. At the end of the 16-week trial, the lottery group dropped an average of 13.1 lb., with 53% reaching the goal. In the deposit-contract group, the average weight loss was 14 lb., with 47% taking off 16 lb. or more. People in the no-incentive group logged an average weight loss of just 3.9 lb., with only 11% of them reaching the 16-lb. goal. As for the payouts? The winning lottery players walked away with an average of $272.80." [Time]