This paper 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 prior to 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 nine 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.

中文翻译：

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社会信号和儿童免疫：塞拉利昂的田间实验


本文探讨了使用社会信号作为可持续影响儿童免疫接种的政策工具。在塞拉利昂公共诊所进行的为期 26 个月的实地实验中，我引入了一个可验证的信号——以颜色编码的手环的形式——在儿童及时完成前四次或全部五次必需的疫苗接种后给予。信号会增加父母对他们行为的可见性和对其他儿童疫苗接种状态的了解的信心。信号的影响会因操作的成本和感知收益而有很大差异。当信号与感知益处低的更容易完成疫苗相关联时，对及时和完全免疫没有明显影响，而当信号与感知益处高、实现成本更高的疫苗相关联时，对及时和完全免疫没有明显影响。父母在实现社会形象益处前 9 个月调整他们的行为，展示了信号激励的激励力量。具有实质性政策重要性的是，手环将一岁儿童的全面免疫接种率提高了 9 个百分点，其影响持续到两岁。以每名完全免疫的儿童 24.7 美元的边际成本，社交信号与经济或实物激励一样具有成本效益。