Assessing the differential effect of poll exposure on voting behaviour

Political polling has come under increased scrutiny in recent years following notable failures to predict the 2015 and 2017 election outcomes, as well as the result of the Brexit referendum. Inquiries undertaken in light of this culminated in a recent House of Lords Select Committee report calling for the polling industry to 'get its house in order', but, notably, rejecting the case for
banning poll publication for any time period. This could partly be explained by the recent finding that such failures do not majorly diverge from the norm of historically endemic inaccuracy, but it has also been framed in terms of the influence of polls on public opinion. That is, pollsters welcomed the Select Committee's conclusions on the grounds that any potential polling blackout, founded on the idea that inaccurate forecasts could unfairly sway the vote, would fail to account for the fact that, in the absence of polls, people could still be influenced by their (even more prone to error) expectations of the outcome. This notion is curious, however, given the large and growing body of research putatively demonstrating the existence of a bandwagon effect, according to which voter exposure to opinion polls gives further advantage to the leading candidate. It would therefore seem, given the evidence presented in this literature, that polls affect electoral outcomes in a way many might deem undemocratic. I argue, however, that such an assertion is jeopardised by conceptual inadequacies within this body of work. Not only is the bandwagon effect loosely and differently defined by different researchers, but also very few attempts have been made at identifying the causal mechanisms through which this effect is had. It may be that the bandwagon effect only exists among certain individuals, contingent on certain characteristics or circumstances, related for example to identity, partisanship, knowledge, emotions, political engagement or efficacy. It may even be that the effect does not exist at all when controlling for the correct alternative explanations. Moreover, while observational studies of this effect have struggled to deal with issues of internal validity, in the absence of clear theoretical expressions of the bandwagon effect, the crucial requirement of maximising experimental realism - by providing theoretically sound treatments - has been overlooked in experimental studies. My thesis, therefore, takes stock of this situation and aims to reorient the literature by clearly defining the concepts at play, hypothesising several mechanisms through which these may operate based on a comprehensive reading of existing scholarship, and testing these through conjoint analysis. This method allows me to engage closely with theory by offering multi-layered, nuanced and realistic treatments, produces an output to which mediation and moderation analyses can be applied to identify clearly which mechanisms are borne out in the data, and directly controls for alternative explanations. In addition to the conceptual contribution of reestablishing how we can think about bandwagon effects and poll effects more broadly, I will thus offer novel empirical insights into how any such effect might be had, if it exists at all, and further our understanding of how conjoint analysis can be deployed in studies of political behaviour.