社会信号与儿童免疫接种：塞拉利昂的一项田野实验

This article explores the use of social signaling as a policy tool to sustainably affect childhood immunization. In a 26-month field experiment with public clinics in Sierra Leone, I introduce a verifiable signal-in the form of color-coded bracelets-given to children upon timely completion of the first four or all five required vaccinations. Signals increase parents' belief in the visibility of their actions and knowledge of other children's vaccine status. The impact of signals varies significantly with the cost and perceived benefits of the action. There are no discernible effects on timely and complete immunization when the signal is linked to an easier-to-complete vaccine with low perceived benefits, and large positive effects when the signal is linked to a costlier-to-achieve vaccine with high perceived benefits. Parents adjust their behavior nine months before realizing the social image benefit, demonstrating the motivational strength of signaling incentives. Of substantive policy importance, bracelets increase full immunization at one year of age by 9 percentage points, with impacts persisting at two years of age. At a marginal cost of US$24.7 per fully immunized child, social signals can be as cost-effective as financial or in-kind incentives.