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WASHINGTON, DC—Washington Legal Foundation (WLF) today released a Monograph on the key principles federal and state judges should follow when assessing the admissibility of expert testimony in civil litigation. Expert testimony not only can decide the outcome of products-liability and toxic-tort lawsuits, but also can impact key rulings such as class-action certification and damages determinations. Judges must act as “gatekeepers,” the U.S. Supreme Court has proclaimed, to shield lay juries from what Justice Antonin Scalia called “expertise that is fausse and science that is junky.”

A team of Mayer Brown LLP attorneys led by a co-leader of the firm’s Supreme Court and Appellate practice, Evan M. Tager, authored Admissibility of Expert Testimony: Manageable Guidance for Judicial Gatekeeping on a pro bono basis. The Monograph features a foreword by Facebook, Inc. Vice President and Deputy General Counsel Paul S. Grewal, who before joining the company served as a United States Magistrate Judge on the U.S. District Court for the Northern District of California.

The Monograph’s first part discusses four aspects of the judicial gatekeeping function that cut across different substantive areas of law. The authors first explain how the Supreme Court’s  “Daubert trilogy” of decisions established the scope of a judge’s gatekeeping duties. They next illustrate how “hired-gun” experts complicate a juror’s task of deciding liability and how courts can mitigate the confusion. They go on to address how courts must answer a “recurring riddle”—does the expert’s testimony implicate the evidence’s admissibility (a judicial function) or does it go to its weight (a jury’s responsibility). Finally, the authors analyze the tools judges can use to weed out junk science, including holding Daubert hearings and appointing independent technical experts.

The Monograph’s second part delves deeper into these critical aspects of gatekeeping through case studies. The authors explore in detail judicial best-practices for determining relevance and reliability in four areas of law: (1) medical causation; (2) insurance bad faith; (3) class-action certification; and (4) valuation testimony for damage calculations. The medical-causation case study offers especially valuable insights on how judges should manage experts testifying on general and specific causation.

Electronic copies of this Monograph are available online at Inquire about additional hard copies with WLF Legal Studies Division Chief Counsel Glenn Lammi (

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