The Healthy Chicago Survey (HCS) is a self-administered, multimode survey conducted annually on a random sample of Chicagoans aged 18 years or older. The survey uses an address-based sampling frame and offers both web and paper modes, with a Choice+ data collection protocol offering a higher promised incentive for completing by web. Overall, about 90% of individuals take the HCS via web. Sampled households are sent a series of mailings inviting the adult who is next to celebrate a birthday to complete the survey. In the 2023 HCS administration, an experiment was fielded in which half of the mailings contained …