Dr. Kevin Volpp, of the University of Pennsylvania School of Medicine, who was concerned that dieting requires deferred gratification and decided to create a a reward system which gave dieters “rewards in the present”. Note the assumption that “the obese” are not capable of deferred gratification. How I’ve managed to spend less than I earn, save for retirement, get a Bachelor of Science, or rehabilitate my knee is a total mystery because I have obviously have no self-discipline whatsoever.
What form did these rewards take? They experimented with 2 forms:
[A] deposit contract, in which participants invested a small amount of their own money — between 1 cent and $3 per day — which they would lose at the end of the month if they failed to reach their goals. People in this group also got a bonus if they met their goal.
I could see this type of program becoming a new staple of “wellness” programs. “Join our Diet Program for $5/week and if you lose weight you’ll get $40 at the end of the month!”
[A] lottery-based design in which participants played a [daily] lottery and were allowed to collect their winnings if they met their weight-loss target.
As the study involved a relatively small group – 57 people divided into 3 groups, one of which used the lottery. If they’re divided evenly then the odds of winning are over once a month. So, one group had a “set” reward, the other had an element of chance.
I am not a psychologist, but I have read about Skinner’s work in reinforcement and that variable reinforcement results in the highest rate of response. It’s the same principal as slot machines.
What were the results?
- They started with 57 people, divided into 3 groups – the lottery group, the deposit group, and the control group.
- All three groups were aiming to lose 16 lbs in 4 months.
- The article states that lotteries were run daily and participants were told how much they won or would have won. It’s not stated how frequently the deposit group received reinforcement.
- The control group were weighed at the end of each month, no other intervention.
- About 1/2 the participants in the lottery and deposit group met their goal of losing 16lbs.
- On average the lottery group lost 13lbs; the deposit group lost 14lbs; and the control group lost 4lbs.
Ah, you may be wondering: Did they keep the weight off? No. Like many other diet studies, the short-term losses were followed by regains.
Dr Volpp attributes this to the money stopping, and is quoted as saying that “We need to establish whether they can be effective in sustaining weight loss as well.” Perhaps he should check into the military’s results with requiring a certain weight range for continued employement. There’s a reason why eating disorders are more prevalent in the military than the general population.
Update: Another take on the study is here.