Persuasive Politics: How Parties Convince in a Fragmented Landscape

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• Department of Political and Social Sciences

This dissertation explores political persuasion in Europe against the backdrop of increased issue-based polarization. Leveraging two survey experiments, the first chapter shows that ambiguous appeals decline in effectiveness as voters attribute greater importance to issues. This suggests that during periods of increased polarisation, mainstream political actors may struggle to form broad coalitions of voters with diverse preferences. The second chapter builds on this implication and discusses which persuasion strategies Green parties may use to appeal to a more diverse part of the electorate. It uses two survey experiments and a field experiment in collaboration with the German Greens. The third chapter uses a survey with Dutch party members and politicians to shed light on another consequence of increased issue-based polarisation—the declining membership numbers of mainstream parties—and examines whether party members or politicians have a more accurate perception of voter positions. Findings indicate that party members, being less biased, may contribute significantly to improving the quality of representation. The final chapter builds upon this conclusion, using two field experiments to explore how parties might motivate their members to greater activism.

Jonne Kamphorst is a political scientist utilising experimental methods to study political persuasion, with a focus on how social divisions influence the various techniques that politicians, parties, and other organizations use to influence public opinion. His work includes survey and field experiments on the politics of coalition building in Europe. Prior to coming to the EUI, he gained an MPhil in Comparative Politics from the University of Oxford and an MSc in Political Sociology from the London School of Economics.