Mobile health technology as a solution to self-control problems: The behavioral impact of COVID-19 contact tracing apps in Japan.

Rationale: Mobile technology has been widely utilized as an effective healthcare tool during the COVID-19 pandemic. Notably, over 50 countries have released contact-tracing apps to trace and contain infection chains. While earlier studies have examined obstacles to app uptake and usage, whether and how this uptake affects users' behavioral patterns is not well understood. This is crucial because uptake can theoretically increase or decrease behavior that carries infection risks.

Objective: The goal of this study is to evaluate the impact of app uptake on the time spent out of home in Japan. It tests four potential underlying mechanisms that drive the uptake effect: compliance with stay-at-home requirements, learning about infection risk, reminders, and commitment device.

Method: We use unique nationwide survey data collected from 4,379 individuals aged between 20 and 69 in December 2020 and February 2021 in Japan. Japan has features suitable for this exercise. The Japanese government released a contact tracing app in June 2020, which sends a warning message to users who have been in close contact with an infected person. We conduct a difference-in-differences estimation strategy combined with the entropy balancing method.

Results: App uptake reduces the time spent out of home. Sensitivity analysis shows that it cannot be explained by unobserved confounders. Importantly, the impact is large even among users who have not received a warning message from the app, and even larger for those with poor self-control ability. Furthermore, individuals' self-control ability is negatively associated with the uptake decision, supporting our hypothesis that the apps serve as a commitment device.

Conclusions: It may be beneficial to encourage citizens to uptake contact tracing apps and other forms of commitment devices. This study also contributes to the literature on mobile health (mHealth) by demonstrating its efficacy as a commitment device.