P OLITICAL ADVERTISING IN CONSOLIDATING DEMOCRACIES :R ADIO ADS , CLIENTELISM , AND POLITICAL DEVELOPMENT IN M EXICO ∗ HORACIO L ARREGUY † J OHN MARSHALL ‡ JAMES M. S NYDER J R . § MAY 2014 Combating disparities in access to political advertising is an essential challenge for many consolidating democracies. Consequently, many countries now regulate access to political advertising in the media. Mexico implemented such a reform in 2007, allo- cating radio and television advertising slots according to national and state vote shares at the previous election. Using media signal coverage data, we combine matching techniques with a fuzzy geographic regression discontinuity design to exploit differ- ences in exposure to political advertising caused by cross-state spillovers to identify the effects of political advertising. We show that political advertising—particularly AM radio—primarily helps political parties that do not rely on clientelistic strategies, but is only effective in the least socioeconomically developed and least politically com- petitive electoral precincts. Political advertising has the capacity to win voters in the PRI’s traditionally clientelistic strongholds. Finally, our results suggest that political advertising persuades rather than mobilizes voters. * We wish to thank Andy Hall, Jonathan Phillips and Maxim Pinkovskiy for comments on earlier drafts. Data and replication code will be made available online upon publication. † Department of Government, Harvard University, hlarreguy@fas.harvard.edu. ‡ Department of Government, Harvard University, jmarsh@fas.harvard.edu. § Department of Government, Harvard University, jsnyder@gov.harvard.edu. 1