Book Review: Chilton & Rozema’s Trial by Numbers: A Lawyer’s Guide to Statistical Evidence

Several times each month, we are pleased to republish a recent book review from the Canadian Law Library Review (CLLR). CLLR is the official journal of the Canadian Association of Law Libraries (CALL/ACBD), and its reviews cover both practice-oriented and academic publications related to the law.

Trial by Numbers: A Lawyer’s Guide to Statistical Evidence. By Adam Chilton & Kyle Rozema. New York: Oxford University Press, 2024. 207 p. Includes list of figures and tables, notes, glossary, and index. ISBN 9780197747858 (hardcover) $90.00; ISBN 9780197747865 (softcover) $35.00.

Reviewed by Katarina Daniels
Research Lawyer, Library Services Lead
Davies Ward Phillips & Vineberg LLP

In Trial by Numbers: A Lawyer’s Guide to Statistical Evidence, authors Adam Chilton and Kyle Rozema offer a timely and welcome introduction to empirical methods tailored for the legal community. Their book provides an accessible and well-structured guide to understanding statistical evidence as it appears in litigation, policy work, and legal scholarship.

One of the book’s notable strengths is its clear and logical progression. Comprising eight chapters, it builds from foundational concepts to more advanced techniques. Chapter 1 sets the stage by outlining the authors’ aims and distinguishing their approach. Rather than teaching readers how to conduct empirical research, Chilton and Rozema focus on cultivating the ability to interpret and critically evaluate statistical reasoning in legal contexts. Chapters 2 and 3 introduce probability and basic statistics, respectively, laying the groundwork for Chapter 4’s discussion of causal inference and experiments. The remaining four chapters focus on the empirical methods most relevant to the legal profession, used for causal inference: regression, difference-in-differences, regression discontinuity, and instrumental variables. These methods are presented in a way that emphasizes their logic and legal relevance.

Each chapter follows a consistent and pedagogically effective structure. Concepts and methods are introduced with a brief overview, followed by a legal example that is carried throughout the chapter. Subsections are clearly delineated, and each chapter concludes with a summary that synthesizes the main ideas and revisits the example to demonstrate how the method helps to investigate or clarify the legal issue at hand.

The exclusive use of legal examples is another of the book’s key strengths. Despite being grounded in American law and social realities, the examples are engaging for readers from other jurisdictions, many of whom will be familiar with the referenced legal controversies through media coverage or will have encountered similar issues in their own legal systems. This legal framing sustains reader engagement while underscoring the importance of empirical literacy in contemporary legal practice.

Thankfully, the authors recognize the needs and limitations of their intended audience. Definitions are repeated where appropriate, and the most important concepts in each chapter are clearly highlighted, while a glossary is available at the end for easy reference. Unlike traditional statistics texts, the book features just a single equation, which is then modified and applied across successive methods. While the authors attempt to simplify the math, the notation may nonetheless be challenging for readers unfamiliar with statistical symbols. Understanding how the equation is crafted and how it should be interpreted can also be difficult. Some sections may benefit from multiple readings, especially as the methods become more complex.

Readers hoping to conduct their own empirical studies will need further training, but that is not the book’s purpose. Chilton and Rozema are transparent about what the book does and does not cover, enhancing its value as a foundational resource for further study. Additionally, they include substantial footnotes directing readers to more advanced materials.

More importantly, the book equips legal professionals to understand and critically evaluate empirical arguments as they appear in expert reports, policy analysis, and legal scholarship. What is particularly useful is that the book enables readers to recognize key concepts and methodological choices in expert reports, fostering a more critical approach to how evidence is framed and interpreted. The presentation of evidence depends on how research questions are constructed, variables are defined, and parameters are selected. Given the many ways in which this statistical evidence can be presented, awareness is essential for legal professionals assessing the credibility and relevance of expert analysis.

Trial by Numbers would be a valuable addition to any legal curriculum that includes empirical methods and is a worthwhile recommendation for practitioners who encounter statistical evidence in their work. As generative AI begins to play a role in shaping expert output, lawyers must be equipped to interpret, assess, and, where necessary, challenge the use and interpretation of data in litigation. This book offers readers a starting point for that critical engagement.