“…While a large empirical literature in political science (Lau et al, 2007) finds a small but positive effect of negative campaigning on voter turnout, and the literature that has examined comparative advertising -of which negative campaigning is one type -has found comparative messages more effective at changing consumers' buying intentions (Grewal et al, 1997), there are few randomized experiments measuring individual behavior on this topic in naturally occurring settings, as such tests impose costs on those running for office. Outside of some notable exceptions (Arceneaux and Nickerson, 2010;Gottfried et al, 2009;Niven, 2006), previous studies frequently measured intentions rather than behavior, used laboratory experiments with synthetic candidates or products, or examined indirect evidence and required strong identification assumptions to reach their conclusions 1 .…”