Prosocial versus self-interested appeals in offline health communication: A randomized trial of framed messages during the COVID-19 pandemic in Switzerland.

Background Research on self-interested and prosocial appeals during COVID-19 has largely relied on online messages and self-reported intentions, leaving limited evidence on their effectiveness in offline health communication. This gap is important, as many preventive behaviors-such as hand hygiene- occur in stimuli-rich, offline environments.Objective To examine the relative effectiveness of prosocial, self-interested, and combined motivational appeals in promoting hand hygiene in an offline retail setting.Methods We conducted a randomized controlled trial in four Swiss supermarkets during the second wave of the COVID-19 pandemic (January 26-29, 2021). Customers (N = 22,791) were exposed to poster messages encouraging hand disinfection. Hand hygiene behavior was directly observed. Treatment effects were estimated using linear probability models with cluster-robust standard errors, and exploratory analyses examined heterogeneity across age groups.Results We find no statistically significant differences in hand disinfection rates between the three motivational-appeal treatments. Prosocial appeals showed slightly higher disinfection rates descriptively, but effects were small. Exploratory analyses suggest heterogeneity across age groups.Conclusions Our findings underscore the importance of testing health messages offline in the environments in which preventive behaviors are actually performed. Future research should examine the overall effectiveness of motivational appeals and heterogeneity across age groups.Classification Codes I120, C930.