Lottery

What is a lottery incentive?

A lottery allocates a prize by chance. In a behavior-change program, eligibility for a draw can depend on completing a specified action. This arrangement should be distinguished from a commercial lottery in which people buy tickets.

Research example

In Volpp and colleagues’ randomized trial, a lottery-based weight-loss program produced more weight loss than the control at 16 weeks. The difference between groups was not statistically significant at seven months.

What to specify

A clear description states the eligible action, chance of winning, prize value, and timing. Expected monetary value combines probability and payout, but participants may value the arrangement differently.

A hypothetical learning incentive

Suppose an employer offers one entry to each employee who completes a voluntary training module by Friday at noon. There is no entry fee. The draw takes place that afternoon, with one $100 prize. If exactly 100 employees qualify, each has one entry and each entry is equally likely to win, an employee’s chance is 1 in 100.

The expected monetary value is (1/100 × $100) + (99/100 × $0) = $1 per entrant. An individual receives either $100 or nothing, not a guaranteed dollar. This describes the arrangement; it does not establish that employees prefer it to a certain $1 payment or that it increases course completion.

Limits

One trial does not show that lotteries outperform guaranteed rewards in general, or that their effects last after incentives end. The follow-up result matters: getting someone to act while a prize is available is different from helping them sustain the behavior afterward.