What About the Precedent: An Information-Theoretic Analysis of Common Law

Josef Valvoda, Tiago Pimentel, Niklas Stoehr, Ryan Cotterell, Simone Teufel


Abstract
In common law, the outcome of a new case is determined mostly by precedent cases, rather than by existing statutes. However, how exactly does the precedent influence the outcome of a new case? Answering this question is crucial for guaranteeing fair and consistent judicial decision-making. We are the first to approach this question computationally by comparing two longstanding jurisprudential views; Halsbury’s, who believes that the arguments of the precedent are the main determinant of the outcome, and Goodhart’s, who believes that what matters most is the precedent’s facts. We base our study on the corpus of legal cases from the European Court of Human Rights (ECtHR), which allows us to access not only the case itself, but also cases cited in the judges’ arguments (i.e. the precedent cases). Taking an information-theoretic view, and modelling the question as a case out-come classification task, we find that the precedent’s arguments share 0.38 nats of information with the case’s outcome, whereas precedent’s facts only share 0.18 nats of information (i.e.,58% less); suggesting Halsbury’s view may be more accurate in this specific court. We found however in a qualitative analysis that there are specific statues where Goodhart’s view dominates, and present some evidence these are the ones where the legal concept at hand is less straightforward.
Anthology ID:
2021.naacl-main.181
Volume:
Proceedings of the 2021 Conference of the North American Chapter of the Association for Computational Linguistics: Human Language Technologies
Month:
June
Year:
2021
Address:
Online
Editors:
Kristina Toutanova, Anna Rumshisky, Luke Zettlemoyer, Dilek Hakkani-Tur, Iz Beltagy, Steven Bethard, Ryan Cotterell, Tanmoy Chakraborty, Yichao Zhou
Venue:
NAACL
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
2275–2288
Language:
URL:
https://aclanthology.org/2021.naacl-main.181
DOI:
10.18653/v1/2021.naacl-main.181
Bibkey:
Cite (ACL):
Josef Valvoda, Tiago Pimentel, Niklas Stoehr, Ryan Cotterell, and Simone Teufel. 2021. What About the Precedent: An Information-Theoretic Analysis of Common Law. In Proceedings of the 2021 Conference of the North American Chapter of the Association for Computational Linguistics: Human Language Technologies, pages 2275–2288, Online. Association for Computational Linguistics.
Cite (Informal):
What About the Precedent: An Information-Theoretic Analysis of Common Law (Valvoda et al., NAACL 2021)
Copy Citation:
PDF:
https://aclanthology.org/2021.naacl-main.181.pdf
Video:
 https://aclanthology.org/2021.naacl-main.181.mp4
Code
 valvoda/Precedent
Data
ECHR