The causal effect of a health treatment on beliefs, stated preferences and memories
中文摘要
本文估计健康治疗对患者关于该治疗的信念、偏好与记忆的因果效应。文章利用英国在新冠疫苗接种运动期间发生的一次自然实验。英国居民可以选择加入疫苗接种计划，但无法选择接种何种疫苗。所分配到的疫苗几乎不提供可用于了解其质量的客观信息，却激发了强烈的、对安心信念的心理需求。我们在英国居民接种前后对其关于不同新冠疫苗的信念进行了抽样调查。接种前，个体对不同疫苗表现出相似的先验信念与陈述偏好。然而接种后，他们对所接种疫苗的安全性和有效性的信念更新得过于乐观，表示若能选择便会选择该疫苗，并且对自身过去信念的记忆出现扭曲。这些结果无法由传统的经验效应解释。在总体层面，这些结果表明随机分配至某种健康治疗会预测对其质量的看法出现极化。在个体层面，这些发现与现实医疗环境中动机性信念及对弱信号过度推断的预测相一致。
Abstract
The paper estimates the causal effect of a health treatment on patients’ beliefs, preferences and memories about the treatment. It exploits a natural experiment which occurred in the United Kingdom during the COVID-19 vaccination campaign. UK residents could choose to opt into the vaccination program, but not which vaccine they received. The assignment to a vaccine offered little objective information for learning about its qualities, but triggered strong psychological demand for reassuring beliefs. We surveyed a sample of UK residents about their beliefs on the different COVID-19 vaccines before and after receiving their jab. Before vaccination, individuals exhibit similar prior beliefs and stated preferences about the different vaccines. After vaccination, however, they update their beliefs overly optimistically about the safety and effectiveness of the vaccine they received, state that they would have chosen it if they could, and have distorted memories about their past beliefs. These results cannot be explained by conventional experience effects. At the aggregated level, they show that random assignment to a health treatment predicts a polarization of opinions about its quality. At the individual level, these findings provide evidence in line with the predictions of motivated beliefs and over-inference from weak signals in a real-world health setting.