13 November 2023

The Use of Precedent in International Economic Disputes: An Empirical Investigation of Citation Networks

How does the use of precedent evolve in international regimes with different institutional setups? In her recently defended PhD thesis in International Law, Chanya Punyakumpol draws on citation data to compare the use of precedent by the WTO network and by the investment network, with the ultimate aim of discovering the main factors that influence Appellate Body members and investment arbitrators to choose which past decisions they would refer to as the benchmark of their decisions. In this interview, she presents her findings, which may inform the current ongoing reform efforts in both the WTO Appellate Body and investment arbitration rules.

How did you come to choose your research topic?

Choosing my research topic was a combination of two factors: what I was interested in and what was available as a research project at the time. 

I have always been a huge fan of applying empirical work to legal research. At Cornell Law School, I took a class called Empirical Legal Research and learned about many research projects that revealed important insights about law and lawmaking (in US domestic law settings). I had done a small project on third-party intervention in WTO disputes myself. From there, I wanted to further develop my work on empirical legal research in international law. 

Then, when I applied for a PhD programme, I came across Professor Pauwelyn’s SNSF project “Convergence versus Divergence? Text-as-Data and Network Analysis of International Economic Law Treaties and Tribunals”. This project was a perfect fit for my research interest, in regard both to the research topic and to the research approach. Fortunately, I got to work on the research project, which also supported my PhD project as well.

These two factors, however, only covered my research approach and the general subject of international law. The idea of studying precedents as a research topic came later after a year of exploring different options. The SNSF project extracted data relating to international economic regimes, free trade agreements, bilateral investment treaties and international economic disputes. While I was exploring the database, I considered several options, from analysing the network of international economic agreements to several aspects of disputes. The citation data, however, stood out as something not many have done the work on. I played around with the citation data and, naturally, the idea of studying judicial citation behaviors led to the concept of precedent. At the same time, the prolonged issue with the WTO’s new Appellate Body member appointment had sparked a debate, among others, on the judicial use of precedent. With these considerations, studying precedent in international economic law disputes seemed appropriate for my PhD project.

To sum up, my interest largely influenced my research approach. The availability of a relevant research project determines the subject of international law. Lastly, the availability of data to work on, along with a great effort in exploring and reading current discussions on issues relating to international law, helped me decide which topic I should work on.

Can you describe your thesis questions and methodology?

Ultimately, my research project wants to find out what are the main factors influencing Appellate Body members and investment arbitrators to choose which past decisions they would refer to as the benchmark of their decisions. To this end, a necessary threshold question that my study must address is whether there is strong evidence of systemic use of past decisions as references, i.e., whether precedent exists at all. This is an important condition to continue further investigation on the influential factors for judicial consideration of precedent. The first research question was therefore framed as follows: How does the use of precedent evolve in international regimes with different institutional setups? In addition to showing proof of the existence of precedent, I also investigated the evolution of those usages. This question has an important legal implication because, as generally understood, there is no formal rule of precedent in international law. However, I wanted to show that practically there is indeed evidence of systemic use of precedent in international economic law. Since the structures of international trade and investment disputes are drastically different, their contrasting institutional setups also serve as a great comparison.

The second research question answers what drives the authority of precedent in international trade and investment disputes, respectively. I approach this research question inductively. This means that I reviewed various legal theories on precedent and categorised their reasonings as potential factors. This includes, for example, the influence of the community of practices, the legal concept of “like cases be treated alike” and the judicial norms established in each regime. Then, I proceeded to empirically prove which factors matter in each regime.

As I have mentioned in my answer to the previous question, my approach was primarily empirical. More specifically, I investigated the use of precedent via actual citation data. I treated judicial citations as proxies for their use of precedent. The use of judicial citation as a proxy for precedent does come with limitations and conditions, however. For example, can one assume that every citation connects to the use of precedent? Probably not. However, I argued that overall, judicial citations serve as the best proxy available for empirical work, as demonstrated empirically by the correlations between the frequency of citations and the importance of certain judicial decisions.

What are your major findings?

The analysis of two citation networks, based on close to 150 WTO Appellate Body reports and 400 investment arbitration awards, first shows the empirical evidence of the systemic uses of precedent in both regimes. However, the nature of how precedent develops differs. It is easier for a highly centralised system like the WTO to develop the use of precedent early on. Yet, a decentralised system is also capable of establishing a strong use of precedent. The study argues that critical junctures, or historical accidents, are crucial for a decentralised system to develop a systemic use of precedent. Such events serve, in other words, as important references for future cases with similar facts.

The second finding answers my second research question about finding out what are the influencing factors for judicial citations, based on the modeling of citation networks. First, the empirical evidence shows that the concept of “like cases be treated alike” is alive and well. Cases tend to cite other cases with similar legal issues. What is more interesting is how the two regimes diverge in the influencing factors. The development of precedent in the WTO, on the one hand, relies heavily on its organisational norms and practices. This is even more evident when the model shows that the community of practices and self-interest factors are not statistically significant. In contrast, the investment network shows strong evidence of community practices and self-interest factors. Investment arbitrators tend to reciprocate citations towards those who have cited them in the past. This “reciprocity” element is particularly lacking in the WTO network.

Can you give an example of a topical issue on which your findings might help shed a new light? 

Fundamentally, the concept of precedent relies on “the logic of maintaining similar outcomes as those that came before”. The issue of precedent arises in both international trade and investment disputes because of the mismatch between (or the lack thereof) the rules on precedent and what is actually practiced by those involved. This study, first and foremost, points out the existence of those mismatches in practice. Secondly, it also provides what contributes to the development of precedent, even without a formal rule. Revealing the effects of these extralegal factors informs the current ongoing reform efforts in both the WTO Appellate Body and investment arbitration rules. If one cannot avoid the use of precedent, even in a regime where prior judicial decisions are not per se binding, the rules of precedent must be clear. This is to avoid undue influence of extralegal factors. The study argues that the keys to better use of precedent are to strike the right check and balance between member states and the judicial branch and to strengthen judicial accountability. Collectively following past decisions should not be used to ensure consistency only for consistency’s sake but for valid legal reasonings through a settled judicial debate.

At a conceptual level, the topic of precedent is timeless. It is always a fascinating topic for legal scholars, particularly those trained in a common law tradition. Expanding empirical work on precedent to international law adds to more enriched discussion theoretically. I do hope that my findings help others in their development of even more nuanced theoretical discussions on precedent in international law.

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Chanya Punyakumpol defended her PhD thesis in International Law in June 2023. Associate Professor Fuad Zarbiyev presided over the committee, which included Professor Joost Pauwelyn and Professor James Hollway, Thesis Co-Supervisors, and Professor Sergio Puig, James E. Rogers College of Law, University of Arizona, USA.

Citation of the PhD thesis: 
Punyakumpol, Chanya. “Precedent and Its Authority in International Economic Disputes: Empirical Investigation of Citation Networks.” PhD thesis, Graduate Institute of International and Development Studies, Geneva, 2023.
Members of the Geneva Graduate Institute can access the thesis via this page of the repository. Others can contact Chanya Punyakumpol at

Interview by Nathalie Tanner, Research Office.
Banner image: part of Figure 5.3, Visualizations of the ISDS Network over time, in Chanya Punyakumpol’s PhD thesis, p. 104.