Reference Manual on Scientific Evidence

Fourth Edition

_______

Committee on Science for Judges—Development of the Reference Manual on Scientific Evidence, Fourth Edition

Committee on Science, Technology, and Law

Policy and Global Affairs

NATIONAL ACADEMIES PRESS 500 Fifth Street, NW Washington, DC 20001

This project is funded in part by the Gordon and Betty Moore Foundation through Grant GBMF10224, and the National Science Foundation under Grant GBMF10224 to the National Academy of Sciences. Any opinions, findings, conclusions, or recommendations expressed in this publication do not necessarily reflect the views of any organization or agency that provided support for the project.

The Federal Judicial Center contributed to this publication in furtherance of the Center’s statutory mission to conduct research and continuing education programs for judicial branch employees for the improvement of judicial administration. This manual is provided as a resource to assist judges in understanding relevant scientific methods and principles that may arise in their cases. The views expressed are those of the authors and not necessarily those of the Federal Judicial Center and its Board.

International Standard Book Number-13: 978-0-309-70123-5
Digital Object Identifier: https://doi.org/10.17226/26919
Library of Congress Control Number: 2025934845

This publication is available from the National Academies Press, 500 Fifth Street, NW, Keck 360, Washington, DC 20001; (800) 624-6242; https://nap.nationalacademies.org.

The manufacturer’s authorized representative in the European Union for product safety is Authorised Rep Compliance Ltd., Ground Floor, 71 Lower Baggot Street, Dublin D02 P593 Ireland; www.arccompliance.com.

Copyright 2025 by the National Academy of Sciences. National Academies of Sciences, Engineering, and Medicine and National Academies Press and the graphical logos for each are all trademarks of the National Academy of Sciences. All rights reserved.

Printed in the United States of America.

Suggested citation: National Academies of Sciences, Engineering, and Medicine and Federal Judicial Center. 2025. Reference Manual on Scientific Evidence: Fourth Edition. Washington, DC: National Academies Press. https://doi.org/10.17226/26919.

NATIONAL ACADEMIES OF SCIENCES, ENGINEERING, AND MEDICINE

The National Academy of Sciences was established in 1863 by an Act of Congress, signed by President Lincoln, as a private, nongovernmental institution to advise the nation on issues related to science and technology. Members are elected by their peers for outstanding contributions to research. Dr. Marcia McNutt is president.

The National Academy of Engineering was established in 1964 under the charter of the National Academy of Sciences to bring the practices of engineering to advising the nation. Members are elected by their peers for extraordinary contributions to engineering. Dr. Tsu-Jae Liu is president.

The National Academy of Medicine (formerly the Institute of Medicine) was established in 1970 under the charter of the National Academy of Sciences to advise the nation on medical and health issues. Members are elected by their peers for distinguished contributions to medicine and health. Dr. Victor J. Dzau is president.

The three Academies work together as the National Academies of Sciences, Engineering, and Medicine to provide independent, objective analysis and advice to the nation and conduct other activities to solve complex problems and inform public policy decisions. The National Academies also encourage education and research, recognize outstanding contributions to knowledge, and increase public understanding in matters of science, engineering, and medicine.

Learn more about the National Academies of Sciences, Engineering, and Medicine at www.nationalacademies.org.

FEDERAL JUDICIAL CENTER

Congress established the Federal Judicial Center to support the efficient and effective administration of the federal courts through research and continuing education of judges and court employees. Its separate status within the judicial branch, its specific missions, and its specialized expertise enable it to pursue and encourage critical and careful examination of ways to improve judicial administration. The Federal Judicial Center has no policymaking or enforcement authority; its role is to provide accurate, objective information and education and to encourage thorough and candid analysis of policies, practices, and procedures.

By statute, the Chief Justice of the United States chairs the Center’s Board, which also includes the director of the Administrative Office of the U.S. Courts and seven judges elected by the Judicial Conference of the United States. The Board appoints the Center’s director and deputy director; the director appoints the Center’s staff. Since its founding in 1967, the Center has had twelve directors. John S. Cooke was director from September 2018–August 2025; Judge Robin L. Rosenberg became director in August 2025. Clara Altman has been deputy director since 2018.

The organization of the Center reflects its primary statutory mandates. The Director’s Office is responsible for the Center’s overall management and its relations with other organizations. The Research Division examines and evaluates current and alternative federal court practices and policies. This research assists the Judicial Conference of the United States. The Center’s research also contributes to its education mission. The Education Division plans and produces education and training for judges and court staff, including in-person programs, video programs, publications, and Web-based programs and resources. The Federal Judicial History Office helps courts and others study and preserve federal judicial history. The International Office provides information to judicial and legal officials from foreign countries and informs federal judicial personnel of developments in international law and other court systems that may affect their work. Two units of the Director’s Office—the Information Technology Office and the Editorial & Information Services Office—support Center missions through technology, editorial, and design assistance, and organization and dissemination of Center resources.

For more information, see www.fjc.gov.

Committee on Science for Judges—Development of the Reference Manual on Scientific Evidence, Fourth Edition

NANCY D. FREUDENTHAL (Co-Chair), Judge, U.S. District Court for the District of Wyoming

FRED H. GAGE (NAS, NAM) (Co-Chair), Adler Professor, Laboratory of Genetics, The Salk Institute for Biological Studies

RUSS BIAGIO ALTMAN, Kenneth Fong Professor of Bioengineering, Genetics, Medicine, Biomedical Data Science, and (by courtesy) Computer Science, Stanford University

DAVID G. CAMPBELL, Senior Judge, U.S. District Court for the District of Arizona

ALICIA L. CARRIQUIRY (NAM), Distinguished Professor of Liberal Arts and Sciences and the President’s Professor of Statistics, Iowa State University

LYNN R. GOLDMAN (NAM), Michael and Lori Milken Dean and Professor of Environmental and Occupational Health, Milken Institute School of Public Health, George Washington University

BRIAN W. KERNIGHAN (NAE), William O. Baker ‘39 Professor, Department of Computer Science, Princeton University

PRAMOD P. KHARGONEKAR, Vice Chancellor for Research and Distinguished Professor of Electrical Engineering and Computer Science, University of California, Irvine

GOODWIN LIU, Associate Justice, Supreme Court of California

SHOBITA PARTHASARATHY, Professor of Public Policy and Women’s and Gender Studies, Ford School of Public Policy and Director, Science, Technology, and Public Policy Program, University of Michigan

PATTI B. SARIS, Judge, U.S. District Court for the District of Massachusetts

THOMAS D. SCHROEDER, Judge, U.S. District Court for the Middle District of North Carolina

DAVID S. TATEL, Judge (retired), U.S. Court of Appeals for the District of Columbia Circuit

National Academies Staff

ANNE-MARIE MAZZA, Project Director and Senior Director, Committee on Science, Technology, and Law, National Academies of Sciences, Engineering, and Medicine

STEVEN KENDALL, Senior Program Officer, Committee on Science, Technology, and Law, National Academies of Sciences, Engineering, and Medicine

RENEE DALY, Senior Program Assistant, Committee on Science, Technology, and Law, National Academies of Sciences, Engineering, and Medicine (until April 2025)

DOMINIC LOBUGLIO, Senior Program Assistant, Committee on Science, Technology, and Law, National Academies of Sciences, Engineering, and Medicine (until February 2023)

MATTHEW COWAN, Christine Mirzayan Science and Technology Policy Graduate Fellow (until May 2023)

Federal Judicial Center Staff

ELIZABETH C. WIGGINS, Director, Research Division, Federal Judicial Center

JASON A. CANTONE, Senior Research Associate, Federal Judicial Center

MEGHAN A. DUNN, Senior Research Associate, Federal Judicial Center

ELLEN URHEIM, AAAS Science & Technology Policy Fellow, Federal Judicial Center (until August 2025); Contractor with Federal Judicial Center (since September 2025)

REBEKAH PETROFF, AAAS Science & Technology Policy Fellow, Federal Judicial Center (until August 2024)

ALEXIS ALLEGRA, AAAS Science & Technology Policy Fellow, Federal Judicial Center (until August 2023)

RESHMINA WILLIAM, AAAS Science & Technology Policy Fellow, Federal Judicial Center (until August 2022)

Consultant

JOE S. CECIL (until June 2024)

Board of the Federal Judicial Center

THE CHIEF JUSTICE OF THE UNITED STATES (Chair)

KATHLEEN CARDONE, Judge, U.S. District Court for the Western District of Texas

R. GUY COLE, JR., Judge, U.S. Court of Appeals for the Sixth Circuit

SARA L. ELLIS, Judge, U.S. District Court for the Northern District of Illinois

RALPH R. ERICKSON, Judge, U.S. Court of Appeals for the Eighth Circuit

MICHELLE M. HARNER, Judge, U.S. Bankruptcy Court for the District of Maryland

SUZANNE MITCHELL, Magistrate Judge, U.S. District Court for the Western District of Oklahoma

LYNN WINMILL, Judge, U.S. District Court for the District of Idaho

ROBERT J. CONRAD, JR., Judge and Director of the Administrative Office of the U.S. Courts

Committee on Science, Technology, and Law

MARTHA MINOW (Co-Chair), Professor of Law, Harvard Law School

HAROLD VARMUS (NAS/NAM) (Co-Chair), Lewis Thomas University Professor, Meyer Cancer Center, Weill Cornell Medicine

DAVID APATOFF, Senior Partner, Arnold & Porter

ERWIN CHEMERINSKY, Dean and Jesse H. Choper Distinguished Professor of Law, University of California, Berkeley School of Law

ELLEN WRIGHT CLAYTON (NAM), Professor of Law, Professor of Health Policy, Vanderbilt University Medical Center

JOHN S. COOKE, Director, Federal Judicial Center (until August 2025)

JENNIFER EBERHARDT (NAS), Professor of Psychology, Stanford University

KENNETH C. FRAZIER, Chairman, Health Assurance Initiatives, General Catalyst

CAROL GREIDER (NAS/NAM), Distinguished Professor of Molecular, Cell, and Developmental Biology, University of California, Santa Cruz

STEVE HYMAN (NAM), Harald McPike Professor of Stem Cell and Regenerative Biology, Core Institute Member and Director, Broad Institute of MIT and Harvard

JON M. KLEINBERG (NAS/NAE), Tisch University Professor, Cornell University

BARBARA MCGAREY, Deputy General Counsel (retired), U.S. Department of Health and Human Services

ERNEST J. MONIZ, Cecil and Ida Green Professor of Physics and Engineering Systems, Post-Tenure, Massachusetts Institute of Technology

KIMANI PAUL-EMILE, Professor of Law, Fordham University Law School

K. SABEEL RAHMAN, Professor of Law, Cornell Law School

NATALIE RAM, Professor of Law, University of Maryland Francis King Carey School of Law

JULIE ROBINSON, Senior Judge, U.S. District Court for the District of Kansas

PATTI B. SARIS, Judge, U.S. District Court for the District of Massachusetts

VICKI SATO, Chair, VIRbio

BARBARA SCHAAL (NAS), Mary-Dell Chilton Distinguished Professor, Washington University in St. Louis

JOSHUA SHARFSTEIN, Vice Dean and Professor, Johns Hopkins Bloomberg School of Public Health

CLIFFORD TABIN (NAS), Leder Professor and Chair, Harvard Medical School

Staff

ANNE-MARIE MAZZA, Senior Director

STEVEN KENDALL, Senior Program Officer

RENEE DALY, Senior Program Assistant (until April 2025)

Reviewers

This Reference Manual on Scientific Evidence was reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise. The purpose of this independent review is to provide comments that will assist the National Academies of Sciences, Engineering, and Medicine in making each publication as sound as possible and to ensure that it meets the institutional standards for quality, objectivity, evidence, and responsiveness to the statement of task. The review comments and draft manuscripts remain confidential to protect the integrity of the deliberative process.

We thank the following individuals for their review of this manual:

HELEN ADAMS, U.S. District Court for the Southern District of Iowa

BRUCE ALBERTS (NAS), University of California, San Francisco

PAOLA ARLOTTA (NAS, NAM), Harvard University

ORLEY ASHENFELTER (NAS), Princeton University

PAUL BARBADORO, U.S. District Court for the District of New Hampshire

JOHN BUTLER, U.S. Department of Commerce

CLEOPATRA CABUZ (NAE), Honeywell Industrial Safety (retired)

FRED CATE, Indiana University

VINTON CERF (NAS, NAE), Google

EDWARD CHENG, Vanderbilt University

ELLEN WRIGHT CLAYTON (NAM), Vanderbilt University

CARL CRANOR, University of California, Riverside

CHRIS FIELD (NAS), Stanford University

ELIZABETH GEDDES, Shihata & Geddes

CHARLES HAAS (NAE), Drexel University

SARA HUSTON, Ann & Robert H. Lurie Children’s Hospital of Chicago

STEVEN HYMAN (NAM), Broad Institute of MIT and Harvard

RAYMOND JACKSON, U.S. District Court for the Eastern District of Virginia

KATHLEEN HALL JAMIESON (NAS), University of Pennsylvania

PAUL JANICKE, University of Houston

KAREN KAFADAR, University of Virginia

MARGARET BULL KOVERA, John Jay College of Criminal Justice

ERIC LANDER (NAS, NAM), Broad Institute of MIT and Harvard

JULIA LEIGHTON, Public Defender Service for the District of Columbia (retired)

PATRICK MALONE, Patrick Malone & Associates

RICHARD A. MESERVE (NAE), Carnegie Science

ROBERT MILLER, U.S. District Court for the Northern District of Indiana

DAVID OWEN, University of South Carolina (retired)

MARIA POLYAKOVA, Stanford University

ANTHONY PORCELLI, U.S. District Court for the Middle District of Florida

WILLIAM PRESS (NAS), The University of Texas at Austin

JED RAKOFF, U.S. District Court for the Southern District of New York

NATALIE RAM, University of Maryland

MARGARET RILEY, University of Virginia

VICTORIA ROBERTS, U.S. District Court for the Eastern District of Michigan (retired)

JULIE ROBINSON, U.S. District Court for the District of Kansas

BARBARA ROTHSTEIN, U.S. District Court for the Western District of Washington

JOELLEN RUSSELL, University of Arizona

JOHN SAMET (NAM), University of Colorado

NATHAN A. SCHACHTMAN, UB Greensfelder

FRANCIS SHEN, Harvard University

MICHAEL SIMON, U.S. District Court for the District of Oregon

WILLIAM SMITH, U.S. District Court for the District of Rhode Island

HAROLD SOX (NAM), Dartmouth University (retired)

HOLDEN THORP, American Association for the Advancement of Science

WENDY WAGNER, The University of Texas at Austin

LYNN WINMILL, U.S. District Court for the District of Idaho

JOHN WIXTED, University of California, San Diego

DIANE WOOD, University of Chicago

DONALD WUEBBLES, University of Illinois

JAMES WYNN, U.S. Court of Appeals for the Fourth Circuit

Although the reviewers listed above provided many constructive comments and suggestions, they were not asked to endorse the Reference Manual on Scientific Evidence, nor did they see the final draft before its release. The review of this edition was overseen by Judge Jed S. Rakoff, U.S. District Court for the Southern District of New York, and Judge Kathleen M. O’Malley (retired), Kate O’Malley LLC. They were responsible for making certain that an independent examination of the manual was carried out in accordance with the standards of the National Academies and that all review comments were carefully considered. Responsibility for the final content rests with the Committee on Science for Judges—Development of the Reference Manual on Scientific Evidence, Fourth Edition, the National Academies, and the Federal Judicial Center.

This page intentionally left blank.

Foreword

I am pleased to introduce this fourth edition of the Reference Manual on Scientific Evidence. A joint product of the Federal Judicial Center and the National Academies of Sciences, Engineering, and Medicine, the manual has for three decades assisted judges in considering all manner of statistical and scientific evidence offered in litigation. In so doing, it has helped bring about better and fairer legal decisions.

It will surprise no one that science and law are today often intertwined. We live in an era of science and technology, with legal controversies reflecting that fact. And no sooner does one scientific field begin to become accessible to judges than another one emerges or fundamentally evolves. In the coming years, judges will confront lawsuits relating, for example, to artificial intelligence, climate science, and epidemiology. Even disputes not about science may involve statistical, survey, or other technical evidence of novel kinds.

Enter this manual. Judges typically are generalists, and they often lack extensive background in the sciences. They can learn, as they do on many subjects, through the adversary process, applying their critical faculties to the claims of parties. But sometimes it also helps to have a dispassionate guide. The manual is the product of close collaboration among highly respected scientists, engineers, judges, and lawyers. It delves into the scientific subjects that judges most often face. It explains scientific approaches and explores scientific uncertainties and limits. It aids in assessing the uses—and the misuses—of scientific and other technical evidence. The manual will hardly resolve every scientific issue arising in the law; that is not, and cannot be, its ambition. Yet case in and case out, the instruction that the manual offers in scientific principles and methods can improve the quality of judicial decision making.

In this way, the Reference Manual on Scientific Evidence exemplifies the benefits that can accrue from cooperation between those proficient in legal analysis and those expert in technical subjects. Judges, along with the lawyers who argue before them, will do their jobs better when they recognize what they can learn from the scientific community. And the law will become stronger as it further reflects sound science.

ELENA KAGAN

Associate Justice

United States Supreme Court

This page intentionally left blank.

Summary Table of Contents

A detailed Table of Contents appears at the front of each reference guide.

Preface

The Admissibility of Expert Testimony

Liesa L. Richter & Daniel J. Capra

How Science Works

Michael Weisberg & Anastasia Thanukos

Reference Guide on Forensic Feature Comparison Evidence

Valena E. Beety, Jane Campbell Moriarty, & Andrea L. Roth

Reference Guide on Human DNA Identification Evidence

David H. Kaye

Reference Guide on Eyewitness Identification

Thomas D. Albright & Brandon L. Garrett

Reference Guide on Statistics and Research Methods

David H. Kaye & Hal S. Stern

Reference Guide on Multiple Regression and Advanced Statistical Models

Daniel L. Rubinfeld & David Card

Reference Guide on Survey Research

Shari Seidman Diamond, Matthew Kugler, & James N. Druckman

Reference Guide on Estimation of Economic Damages

Mark A. Allen, Carlos Brain, & Filipe Lacerda

Prologue to the Reference Guide on Exposure Science and Exposure Assessment, the Reference Guide on Epidemiology, and the Reference Guide on Toxicology

Reference Guide on Exposure Science and Exposure Assessment

M. Elizabeth Marder & Joseph V. Rodricks

Reference Guide on Epidemiology

Steve C. Gold, Michael D. Green, Jonathan Chevrier, & Brenda Eskenazi

Reference Guide on Toxicology

David L. Eaton, Bernard D. Goldstein, & Mary Sue Henifin

Reference Guide on Medical Testimony

John B. Wong, Lawrence O. Gostin, & Oscar A. Cabrera

Reference Guide on Neuroscience

Henry T. Greely & Nita A. Farahany

Reference Guide on Mental Health Evidence

Kirk Heilbrun, David DeMatteo, & Paul S. Appelbaum

Reference Guide on Engineering

Chaouki T. Abdallah, Bert Black, & Edl Schamiloglu

Reference Guide on Computer Science

Brian N. Levine, Joanne Pasquarelli, & Clay Shields

Reference Guide on Artificial Intelligence

James E. Baker & Laurie N. Hobart

Reference Guide on Climate Science

Jessica Wentz & Radley Horton

Appendix. Biographical Information of Committee and Staff

Preface

This fourth edition of the Reference Manual on Scientific Evidence is the product of an ongoing collaboration between the Federal Judicial Center and the National Academies of Sciences, Engineering, and Medicine. The contributions of content by distinguished scholars from across disciplines have resulted in an impartial and reliable primary reference source on science for judges, which we set as our goal. We are grateful to the National Science Foundation and the Gordon and Betty Moore Foundation for the support that made this new edition possible.

Much has changed since the publication of the first edition of the Reference Manual on Scientific Evidence in 1994. Over the years, judges have become more comfortable in exercising a “gatekeeper” function over the admissibility of scientific evidence. Nevertheless, litigation is becoming ever more complex, and aggregate litigation now represents a larger share of the federal civil docket. Scientific, medical, and engineering evidence has also become more complex, and judges must often wrestle with unfamiliar and emerging science and technology. As a consequence, the rules governing admissibility have been revised to deal with emerging problems. For example, amendments to Rule 702 of the Federal Rules of Evidence were recently adopted to discourage testifying experts from overstating the value of evidence underlying such testimony. The dynamic and evolving presence of science in litigation necessitates engagement between the scientific and legal communities. The fourth edition of the Reference Manual on Scientific Evidence reflects this reality.

The primary (but not exclusive) audience for the manual is members of the judiciary who face challenging evidentiary issues related to science and technology. The manual is intended to assist judges in identifying issues commonly in dispute and to help judges reach an informed and reasoned assessment of those issues based on expert evidence that is faithful to the law and within the boundaries of scientifically sound knowledge. The manual is not intended to instruct judges concerning what evidence should be admissible or to establish minimum standards for acceptable scientific testimony.

In the new edition, all reference guides from the previous edition have undergone extensive revision or have been written by new authors. New guides have been added to address eyewitness identification, computer science, artificial intelligence, and climate science, along with a new foreword from Associate Justice of the U.S. Supreme Court Elena Kagan.

We are honored to have co-chaired the committee tasked with the development of this new edition of the Reference Manual on Scientific Evidence. Convened under the auspices of the National Academies’ Committee on Science, Technology, and Law, the committee comprised six judges and seven experts from across science and engineering. All have given generously of their time, judgment, and wisdom to produce a volume that provides a crucial resource for the legal and scientific communities.

We are especially grateful to the authors who worked so diligently in drafting manuscripts for the committee’s review and who responded so thoughtfully to the committee’s and external reviewers’ comments.

We are also grateful for the input of federal judges who responded to a December 2020 survey about how they used the manual and any changes and additions they thought would make it more helpful and to the co-chairs of the National Academies’ 2021 workshop entitled Emerging Areas of Science, Engineering, and Medicine for the Courts.¹ The survey responses, the workshop, and 2019 and 2020 discussions² on science and the courts convened by Dr. Marcia McNutt, president of the National Academy of Sciences, identified many topics and issues that appear in this new edition of the manual.

Additionally, the committee received substantial encouragement from John Cooke, former director of the Federal Judicial Center, and Alan Thompkins, former deputy division director, acting division director, and acting deputy assistant director in the Social, Behavioral and Economic Sciences Directorate. The committee benefitted greatly from the work of Federal Judicial Center staff, particularly Meghan Dunn and Jason Cantone, and from the staff of the National Academies, particularly Steven Kendall, Renee Daly, and Dominic LoBuglio, and from editors Sally-Anne Cleveland, Nathan Dotson, Susanna McCrea, Clare O’Shea, and particularly Geoffrey Erwin.

Special commendation goes to Joe Cecil, project consultant, and Anne-Marie Mazza, project director and senior director of the Committee on Science, Technology, and Law of the National Academies, along with Beth Wiggins, Research Division director for the Federal Judicial Center. Their many contributions in shepherding the manual to completion have been invaluable.

NANCY D. FREUDENTHAL AND FRED H. GAGE

Committee Co-Chairs

1. See https://www.nationalacademies.org/science-for-courts-workshop.

2. Science in the Courts: Amicus Briefs and the Law, Feb. 2019; and Responsiveness of National Academies’ Reports to the Needs of the Courts, Nov. 2020. These discussions were supported by the Ralph J. Cicerone Endowment Fund and the Annenberg Foundation Trust at Sunnylands.