Does differentiated integration strengthen the democratic legitimacy of the EU? Evidence from the 2015 Danish opt-out referendum

Differentiation has become a durable feature of European integration but we know little about its effects on citizens. Does differentiated integration improve the democratic quality of the European Union and strengthen citizens’ support – or does it promote political divides and foster citizens’ alienation from European integration? This article develops a theoretical argument on the positive attitudinal effects of differentiated integration, contending that differentiation accommodates heterogeneous preferences in a diverse EU and strengthens citizens’ ownership of European integration. A quasi-experimental analysis of public opinion of the 2015 Danish Justice and Home Affairs opt-out referendum demonstrates that the public vote increased citizens’ EU efficacy, indeed. Eurosceptic voters in particular strengthen their belief that their individual voice counts in EU politics, suggesting that differentiation can have a positive effect on the perceived democratic quality of the EU.