A City-Wide Experiment Testing the Impact of Geographically-Targeted, High-Payoff Vaccine Lotteries
Katherine L. Milkman, Linnea Gandhi, Sean F. Ellis, Heather N. Graci, Dena M. Gromet, Rayyan S. Mobarak, Allison M. Buttenheim, Angela L. Duckworth, Devin Pope, Ala Stanford, Richard Thaler & Kevin G. Volpp. “A citywide experiment testing the impact of geographically targeted, high-pay-off vaccine l
66 Pages Posted: 16 Aug 2021 Last revised: 17 Oct 2022
Date Written: August 13, 2021
Lotteries have been shown to motivate behavior change in many settings, but their value as a policy tool is relatively untested. We implemented a pre-registered, city-wide experiment to test the effects of three, high-payoff, geographically-targeted lotteries designed to motivate adult Philadelphians to get their COVID-19 vaccine. In each drawing, residents of a randomly selected “treatment” zip code received half the lottery prizes, boosting their chances of winning to 50-100x those of other Philadelphians. The first treated zip code, which drew considerable media attention, may have experienced a small bump in vaccinations compared to control zip codes: average weekly vaccinations rose by an estimated 61 per 100,000 people per week (+11%). Pooling results from all three zip codes treated during our six-week experiment, however, we do not detect any overall benefits. Further, our 95% confidence interval provides a 9% upper bound on the net benefits of treatment in our study.
Funding Information: Funding for this project was provided by Flu Lab, the Behavior Change for Good Initiative at the University of Pennsylvania, and the Center for Health Incentives and Behavioral Economics at the University of Pennsylvania.
Declaration of Interests: Kevin G. Volpp is a part-owner of VAL Health, a behavioral economics consulting firm, all others have nothing to declare.
Ethical Approval Statement: Prior to implementation, the design for the Philly Vax Sweepstakes was reviewed and approved by the institutional review boards (IRBs) of the University of Pennsylvania and the City of Philadelphia. Our study’s analysis plan was pre-registered at osf.io/gxsa4.
Keywords: COVID-19, regret lottery, vaccination, vaccine hesitancy, field experiment, behavioral science, incentives
JEL Classification: D91, C93, I12, I18, Z18
Suggested Citation: Suggested Citation