Do social media ads matter for political behavior? A field experiment

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 par-ticipants 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 can-not 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.(C) 2022 Elsevier B.V. All rights reserved.