Also known as: expert testimonies · expert evidence · expert witness testimony
Written by attorneys · grounded in primary & secondary sources — see below
Testimony given by a witness qualified by knowledge, skill, experience, training, or education that assists the trier of fact to understand the evidence or to determine a fact in issue. The testimony must rest on sufficient facts or data and reliable principles and methods applied reliably to the facts of the case.
Ethan Evans, an engineer retained by Eclipse Manufacturing, testifies about the cause of a machine failure based on his review of design documents and industry standards. No evidence shows that Evans personally observed the machine in operation. The court admits the testimony because the personal-knowledge requirement does not apply to expert testimony.
Emanuel Escobar offers expert testimony that a chemical exposure caused Ezra Eastman's neurological symptoms. The district court examines whether the expert's methodology has been tested, subjected to peer review, and generally accepted in the field. Finding the opinion reliable and relevant, the court admits the testimony.
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Edward Everett's expert concludes that a product design caused Emmett Egan's injury. The data show only that similar products have caused injuries in other settings. The district court excludes the testimony because the analytical gap between the data and the expert's conclusion is too great.
Esme Ellington, an engineer, testifies about the structural integrity of a bridge based on specialized technical analysis. The court applies a flexible reliability inquiry and admits the testimony after confirming that the methods are appropriate for engineering expertise.
Plaintiffs in a limited-fund class action present expert testimony estimating the defendant's total potential liabilities. The court relies on the expert's projections to determine whether the fund is inadequate to satisfy all claims.
A defendant offers expert testimony on eyewitness identification accuracy. The court excludes two of the three proposed opinions because they would not assist the jury under the helpfulness standard for expert testimony.
Expert testimony is admissible and often necessary when a contract uses technical terms of art within a specialized industry. Courts rely on such testimony to establish the customary technical meaning that governs interpretation absent contrary intent.
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The personal-knowledge requirement does not apply to expert testimony. An expert may base an opinion on facts or data that the expert has not personally observed, provided the opinion rests on reliable principles and methods.
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Appellate courts review a district court's decision to admit or exclude expert testimony for abuse of discretion. The trial court acts as gatekeeper and may exclude testimony when there is too great an analytical gap between the data and the proffered opinion.
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…before us. Daubert v. Merrell Dow Pharmaceuticals, Inc. , 951 F.2d 1128, 1131 (9th Cir.1992). The standard for admissibility of expert testimony in this circuit at the time was the so-called Frye test: Scientific evidence was admissible if it was based on a scientific technique generally accepted as reliable within the scientific…