Political Choices: The effect of additional parties on voter decision-making in the UK

This thesis explores the effects of additional parties on the decision-making processes of UK voters in lab-based studies. Specifically, it is concerned with the idea that intrinsic aspects of the democratic system, such as the inclusion of additional parties in an election, can reduce the likelihood of ‘correct voting’ (a voter choosing the candidate whose policies best match their own policy preferences). Firstly, how correct voting is affected by increasing choice set size (i.e. the number of candidates available to choose between). We also examine how a suspected partisan heuristic, ‘party label’, affects rates of correct voting. We conduct four experiments using dynamic information environments, and materials from the five main UK political parties. Results show increasing choice set size negatively predicts voters’ ability to choose the best available option in the choice set. Results for party label are mixed, but strongly suggest party label acts as a beneficial aid to correct voting and may act to offset the effects of increasing choice set size. Secondly, we analyse the patterns of information processing from the previous experiments, creating novel metrics of heuristic processing. We find party label and choice set size affect voters’ information processing, namely the amount and equality of search between alternatives. Finally, we examine the effect of additional alternatives on political decision-making via the established ‘context effects’ paradigm. We test the ‘attraction’, ‘similarity’, ‘compromise’, and ‘phantom’ effects in a series of fictional and more realistic political scenarios, culminating in a field study during the 2015 UK General Election. We find evidence for the attraction and similarity’ effects, but inconsistent evidence for other context effects; and that asymmetric dominance patterns exist in a minority of UK voters’ political preferences (in contrast to a previous finding in the U.S)