Political Advertising and Voting Intention: Evidence from Exogenous Variation in Ads Viewership
Mexico’s campaign law assigns TV and radio ads to parties according to their vote share in the previous election, and mandates the time of the day at which ads are aired to be determined randomly. We exploit this arguably exogenous variation in viewers’ exposure to political ads by different parties and longitudinal electoral survey data to estimate the effect of ads on voting intentions during Mexico’s 2012 presidential campaign. We find that political ads on both radio and TV have a positive, significant and sizeable effect on voting intentions. This effect is short-lived (about two weeks), and is stronger in the early weeks of the campaign. Ads tend to have no significant impact on voters’ knowledge of candidates’ political message, and to be more effective at convincing individuals that are more educated, and those who voted for the party in the past. Taken together these findings suggests that ads do not influence voters by conveying new information but that other mechanisms of persuasion, cantered around ads’ non-informative content, may be at work.