Spillover Effects in Political Advertising: Evidence from Judicial Elections

We develop a simple theory of information spillovers within political advertising: individuals use information conveyed by candidate-specific ads to evaluate other candidates seeking different offices. We test the theory by linking state court of last resort election returns with a complete set of gubernatorial, congressional, and state supreme court political advertisements in 2010. We show that up-ballot advertisements about crime have spillover effects on judicial race outcomes. Specifically, fearful references to crime in non-judicial campaign advertisements decrease judicial incumbent vote share, while enthusiastic references to crime increase incumbent vote share. We estimate that cumulative spillover effects from crime ads in gubernatorial and congressional advertising campaigns in 2010 decreased incumbent justices' average expected vote share, affecting the outcome of at least one state supreme court election in 2010. We show that ads affect vote choice by providing information to voters, rather than by priming local crime rates. We also conduct two placebo tests to validate our results. Overall, these findings provide evidence of ads' political effectiveness, while our research design proposes a conceptual framework for understanding advertising effects in context.