Does differentiated integration weaken parliamentary involvement? Evidence from the European Union's interparliamentary conferences

Does differentiated integration undermine the motivation of parliamentarians from less integrated member states to become involved in European Union affairs? Focusing on the European Union's new interparliamentary conferences in economic governance, and justice and home affairs, this study examines whether voluntary and involuntary as well as comprehensive and partial differentiation influence parliamentary involvement, measured as participation in interparliamentary conferences. Based on new data and Coarsened Exact Matching, the results indicate that the effect of differentiation depends on its political origins and design. Only voluntary and comprehensive differentiation depress parliamentary involvement. The results can be seen as favourable regarding the legitimacy of differentiation and compatible with the European Union's ambition to limit the institutional implications of differentiation. They also indicate a targeted parliamentary response to differentiated integration.