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We are witnessing increasing partisan polarization in many parts of the world. It is often argued  that partisan ‘echo chambers’ are one of the drivers of both policy and affective polarization. In this paper we test that argument. We use an innovative, large-scale pre-registered ‘lab-in-the-field’ experiment to examine how polarization is influenced by partisan group homogeneity. We recruit partisans, who are broadly representative of the British population, and assign them to discussion groups about a salient policy issue. Subjects find themselves with either like-minded partisans (an echo chamber) or a mixture of in-group and out-group partisans. This novel experimental design enables us to examine how group composition affects polarization in a setting that attempts to replicate the real world. We find support for the hypotheses that partisan echo chambers increase both policy and affective polarization. This has important implications for our understanding of the drivers of polarization and for how outgroup animosity might be ameliorated in the mass public.


Professor Sara B. Hobolt is the Sutherland Chair in European Institutions at the London School of Economics and Political Science. She has published widely on elections, referendums and European politics, including her recent book Political Entrepreneurs. The Rise of Challenger Parties in Europe (with Catherine De Vries, PUP 2020).