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 participants to hide political ads (treatment) or alcohol ads (control) for several weeks preceding the 2020 US elections. While the overall modest effect on turnout was insignificant, this masked important heterogeneity, with political ads making Democrats slightly more motivated to vote and Republicans – substantially less. We explore 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