In this paper, we develop a discourse quality index (DQI) that serves as a quantitative measure of discourse in deliberation. The DQI is rooted in Habermas' discourse ethics and provides an accurate representation of the most important principles underlying deliberation. At the same time, the DQI can be shown to be a reliable measurement instrument due to its focus on observable behavior and its detailed coding instructions. We illustrate the DQI for a parliamentary debate in the British House of Commons. We show that the DQI yields reliable data and we discuss how these data could be used in subsequent analysis. We conclude by discussing some limitations of the DQI and by identifying some areas in which it could prove useful.

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Competing interests: A.Fu. serves on the Board of Directors of Common Cause and Everyday Democracy and is an occasional consultant to Apple.

'Deliberative politics' refers to the role of conversation and arguments in politics. Until recently discussion of deliberative politics took place almost exclusively among political philosophers, but many questions raised in this philosophical discussion cry out for empirical investigation. This book provides the first extended empirical study of deliberative politics, addressing, in particular, questions of the preconditions and consequences of high level deliberation. Using parliamentary debates in Germany, Switzerland, the United Kingdom and the United States as an empirical base, the authors measure the level of deliberation by constructing a 'Discourse Quality Index'. As deliberative politics moves to the forefront of political theory, this book makes an important contribution to deliberative democracy.

We define deliberation minimally to mean mutual communication that involves weighing and reflecting on preferences, values, and interests regarding matters of common concern. Deliberative democracy incorporates the requirements that deliberation take place in contexts of equal recognition, respect, reciprocity, and sufficiently equal power for communicative influence to function. These aspirational ideals have inspired a flourishing field, with theoretical and empirical research across many disciplines, and many democratic innovations and practices in many countries and cultures. We survey the evolution of the ideals of deliberative democracy, their numerous sites in deliberative systems, the places of these sites within broader political arenas, and the many critics, criticisms, and revisions the concept and practice of deliberative democracy have attracted.