Dr Hubert Smekal co-authored a paper titled "Different yet the same? Differentiated integration and flexibility in implementation in the European Union". It is out in open access in West European Politics, a top-tier political science journal. Sebastiaan Princen (Utrecht), Frank Schimmelfennig, Ronja Sczepanski (both ETH Zürich), Hubert Smekal (Maynooth) and Robert Zbiral (Brno) investigate the relationship between various modes of the EU's dealing with the heterogeneity of its member states.
The article finds that differentiated integration (opt-outs from directives) and flexibility in implementation (providing leeway to states in directives) tend to appear together. However, they are used to address different aspects of a common underlying set of concerns.