Linking Differentiated Integration and Compliance – Same-Same but Different?

Non-compliance as well as differentiated integration have been discussed as the two dominant strategies in the EU to reduce heterogeneity between member states. However, while differentiated integration is transparent, decided by consent between member states and legal, non-compliance is illegal and by definition untransparent, and decided by a member state alone. Thus, this paper asks the question if differentiated integration can reduce non-compliance in secondary law. We first show that reasons for the occurrence of differentiated integration and non-compliance have been theorized to be the same – the lack of capacity or diverging preferences. Thus, as both mechanisms have, theoretically, the same heterogeneity as root cause, we assume that differentiated integration may prevent the existence of non-compliance. In order to test this hypothesis, we combine two major data sources, the Berlin Infringement data base and the EUDIFF2 data set, covering all secondary legal acts from 1970 until 2012. We show that differentiated integration does not help to foster compliance. However, the patterns differ for country clusters, as Western member states, compliance is increased by differentiated integration, but not for eastern and southern European countries. Afterwards, we discuss several reasons why differentiated integration may not be an avenue to decrease rates of non-compliance for some member states and not for others. This puzzling finding encourages further research on the sources of heterogeneity of differentiated integration and non-compliance.