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Conflict and Cooperation in the EU Heterarchical Legal System

Periodic Reporting for period 4 - EUTHORITY (Conflict and Cooperation in the EU Heterarchical Legal System)

Reporting period: 2020-03-01 to 2021-02-28

The EUTHORITY Project investigates patterns of conflict and cooperation between domestic and supranational courts in the European Union legal system. The generic question it seeks to answer is why and when national judges choose to cooperate and why when they choose to resist the authority of supranational courts.

Organizations and supranational legal regimes like the EU have very limited enforcement capacities. For that reason, the effectiveness of their laws depends on the support of domestic actors such as domestic courts. Domestic judges, though, are not on the EU payroll. The EU cannot promote, demote or fire them. Nor do EU courts have the power to reverse their doctrinal determinations. This heterarchical setting creates opportunities for domestic judges to resist the authority of EU law and to negotiate the terms under which they cooperate with EU judges. As intermittent defiance coexists with patterns of active compliance and pockets of covert disobedience, the absence of a judicial hierarchy can affect the reach of supranational rulemaking and result in fragmented and unequal judicial enforcement. While such a decentralised legal system may be favoured by those who wish to limit the power of ECJ judges, it may also produce inequalities in the application of EU law across courts and EU member states. These disparities have direct, practical implications for EU citizens.

The overall aim of the EUTHORITY Project is to document and identify the factors that determine the position of domestic peak courts--i.e. supreme and constitutional courts--towards EU law and legal integration. Towards that end, the investigators model strategic dynamics within the EU multi-level judiciary and undertake to collect and analyse data on the organizational structure, attitudes and decisions of peak courts across all EU-28 member states.

Completed in February 2021, the Project has produced new knowledge and data sets on the factors and dynamics -- including institutional constraints, resources and ideology -- affecting interactions and tensions among courts in the European Union judiciary while advancing the application of novel methods such as machine learning and Natural Language Processing to the study of EU legal and judicial texts.
Over the 66 months of the Project, the research team has developed its theoretical framework, collected large amounts of data on preliminary references, ECJ opinions and domestic decisions on the relationship between EU law and national law, completed an EU-wide expert survey and tested numerous hypotheses using state-of-the-art data science techniques.

Theoretical efforts have helped sharpen our understanding of judicial motivation with respect to both conflict and cooperation. Theoretical elaborations have considered the role of ideology, institutional constraints, workload and available resources. The team also made advances to implement a game-theoretic online experiment using the oTree platform.

To fill gaps in pre-existing research and open up new ways to test hypotheses derived from our theoretical frame work, the team collected more data than originally planned . Data-collection has been facilitated by the use of data-harvesting techniques, which the team learned to master. The Domestic Judicial Response (DJR) dataset has been completed for all 28 member states, compiling information on more than 300 domestic opinions on more than 50 variables. Progress has also been made on the development of a EU-law detector for Belgian court rulings applying supervised machine learning. Various datasets on preliminary references, some of which compiles information on the geographic coordinates (GEOCOURT Dataset), level and type of the referring courts in addition to several other indicators, have been constructed. The team also completed the JUDICIARY dataset on domestic top courts for all member states. The entire universe of ECJ judgments was scraped from the CURIA and EUR-Lex websites. After cleaning and pre-processing this data, text-mining methods were applied to construct topic models of the case law and investigate issue attention across procedures. The team also completed the EU law expert survey—the EU Law Barometer. Several hundreds judges in Croatia and Slovenia participated in surveys of judicial attitudes towards EU law. Two PhDs funded by the Project were defended -- Monika Glavina (January 2020) defended a thesis on the reception of EU law by Slovenian and Croatian judges and Michal Ovadek (September 2021) a thesis on legal basis disputes.

Dissemination efforts have already resulted in 19 articles in peer-reviewed journals (which does not include papers published in Utrecht Law Review, European Journal of Legal Studies and Croatian Yearbook of European Law and Policy, which don't have DOI number). Other papers have been accepted by law journals (German Law Journal, Erasmus Law Review, Austrian Journal of Public Law, Ratio Juris), are at the review stage or are being prepared for submission. Along with previously mentioned, several working papers have been posted on SSRN and ResearchGate. The Project and papers it has spawned have been presented at various conferences and workshops around Europe. The PI has delivered keynote presentations in the United States (first workshop on Natural Legal Language Processing) and Slovenia (workshop on ideology in judicial decision making). The team has also been involved in the organisation of the first Conference on Empirical Legal Studies in Europe (CELSE) held in Amsterdam in 2016 as well as the second CELSE, which took place in Leuven on 31 May – 1 June 2018. The Conference is a major international event across the disciplines of law, economics and political science and, as such, an important channel to advertise the Project. Besides CELSE 2016 and 2018, the team has organized a seminar series featuring prominent scholars at the intersection of law, economics and political science. The website of the Project ( along with the website of the EU Law Barometer survey ( – the Project’s expert survey) has been another avenue to disseminate the Project’s initiatives, findings and deliverables. Finally, project publications, data and visuals have been disseminated on social media platforms (LinkedIn, Twitter) and blogs ( Verfassungsblog).
EUTHORITY has moved research on the EU judiciary beyond the state of the art at several levels. First, by developing new theories and hypotheses about in-court interactions in non-hierarchical court systems (this includes motives of cooperation for national courts, response to negative feedback, effect of uncertainty arising from events such as Brexit), the Project has contributed new perspectives on the inner workings of the EU judiciary. Second, by constructing new data sets and applying a varied set of quantitative methodologies (item response modelling, expert survey designs, text-mining...) the team has been able to measure empirically the ideological distance between EU judges and other EU institutions, to test models regarding the impact of ideological preferences on EU court decisions, to assess the effect of treaty negotiations on infringement rulings and to investigate the role of case initiators (including domestic judges) on issue attention in EU court cases. The data sets generated by the Project will inform research on the EU judiciary for the years to come.
Article 267 references 1961-2014
Topic model of preliminary rulings (1961-2015) represented as network