Going negative when spoiled for choice? Destabilizing and boomerang effects of negative political messaging in multiparty systems with multimember districts

Classical electoral behaviour theories have associated possible benefits of negative campaigning with two-party plurality systems due to their zero-sum nature. Nevertheless, negative campaigning is a widely used electoral strategy outside of these contexts, despite scant evidence of its benefits for political parties and candidates who employ it. Our research question is simple – is negative campaign messaging effective for attackers in multiparty systems with multimember districts? Or does it create a ‘boomerang effect’ in this context, for which the producer of the message faces a backlash? Multiparty systems with multimember districts should, according to the literature, be scenarios where the effects of negative campaigning are most complex if not unpredictable. This paper uses Facebook political messages to inform a survey experiment design that tests the effects of negative political messaging on voters. We employ this survey in Ireland, which uses the single transferable vote, an electoral system which magnifies outcome uncertainty for attackers. Our results suggest that negative messaging in this context produces both the intended effect and a boomerang effect for the sponsor of the message. These countervailing results suggest a net null effect for the efficacy of negative messaging.