中文摘要
Facebook 推出了可隐藏信息流中广告的过滤器，我们利用这一独特机会研究在线广告对政治行为的影响。在一项预注册实验中，我们将参与者随机分配至隐藏政治广告的处理组或隐藏酒类广告的对照组，两组隐藏相应广告的安排均在2020年美国大选前持续数周。我们报告的政治广告对投票率的意向处理效应为2.3个百分点，在统计上不显著，但无法排除存在较大的正向效应，其95%置信区间为[-2.8, 7.4]个百分点。这一结果可能掩盖了重要的异质性：政治广告使民主党人的投票动机略有增强，却使共和党人的投票动机大幅减弱。我们探讨了这一效应的原因，例如广告内容的自然差异：用户信息流中的大多数 Facebook 广告偏向民主党。最后，政治广告对情感极化和知情程度指标的影响可忽略不计。
Abstract
We exploit Facebook’s introduction of a filter hiding ads from the feed as a unique opportunity to study the effects of online ads on political behavior. In a pre-registered experiment, we randomly assigned participants to hide political ads (treatment) or alcohol ads (control) for several weeks preceding the 2020 US elections. We report an insignificant intent-to-treat effect of political ads on turnout ( 2.3 pp.), but we cannot rule out a sizable positive effect, with 95 % confidence interval of [ - 2.8 , 7.4 ] . The result may mask important heterogeneity, with political ads making Democrats slightly more motivated to vote and Republicans – substantially less. We explore the reasons for this effect, such as natural variation in ad content: the majority of Facebook ads on users’ feeds skewed Democratic. Lastly, the effect on measures of affective polarization and informedness was negligible.