Why have referendums on European integration proliferated since the 1970s? How are referendums accommodated within member states' constitutional orders and with what impact on the European integration process? What is the likely institutional impact of referendums on the future of the European integration process? Drawing on an interdisciplinary approach, these are just some of the fundamental questions addressed in this book. The central thesis is that the EU is faced with a 'direct democratic dilemma', which is compounded by the EU's rigid constitutional structure and a growing politicisation of the referendum device on matters related to European integration. Referendums and the European Union discusses how this dilemma has emerged to impact on the course of integration and how it can be addressed.

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Low-dimensional spatial representations of political preferences are a widespread feature of voting advice applications (VAAs). Currently, VAA spatial maps tend to be defined on the basis of a priori reasoning. This article argues that VAA spatial maps should be empirically validated to safeguard fundamental psychometric properties -in particular, unidimensionality and reliability. We suggest dynamic scale validation as a pragmatic method for improving measurement quality in VAA spatial maps. The basic logic of dynamic scale validation is to exploit early user data as a benchmark against which ex-ante defined maps can be evaluated. We draw on data from one of the most institutionalised VAA settings, Switzerland, to illustrate this dynamic approach to scale validation.

We present our approach to online popularity and its applications to political science, aiming at the creation of agentbased models that reproduce patterns of popularity in participatory media. We illustrate our approach analyzing a dataset from Youtube, composed of the view statistics and comments for the videos of the U.S. presidential campaigns of 2008 and 2012. Using sentiment analysis, we quantify the collective emotions expressed by the viewers, finding that democrat campaigns elicited more positive collective emotions than republican campaigns. Techniques from computational social science allow us to measure virality of the videos of each campaign, to find that democrat videos are shared faster but republican ones are remembered longer inside the community. Last we present our work in progress in voting advice applications, and our results analyzing the data from choose4greece.com. We show how we assess the policy differences between parties and their voters, and how voting advice applications can be extended to test our agentbased models.

Scholars seeking to understand political competition in Europe have proposed various models of political dimensionality. While most scholars draw on data from the supply side of politics (political parties), demand-side (voter) studies remain few. In this article we compare the two approaches. The main difference is that while supply-side approaches suggest a single model of dimensionality that can be applied to all EU countries, demand-side approaches suggest a greater degree of divergence. In particular, the bundle of issues commonly identified by supply-side studies as TAN/GAL not only fail to form a coherent dimension when viewed from a demand-side perspective, but incorporate issues of EU integration in some (northern European) cases, but not in others.