Also known as: expert opinions · expert testimony
Written by attorneys · grounded in primary & secondary sources — see below
Testimony by a witness qualified through specialized knowledge, skill, experience, training, or education that helps the trier of fact understand evidence or determine a fact in issue. The testimony need not rest on the witness's personal perception of the events at issue.
Eric Espinoza, a forensic accountant, reviewed ledgers and transaction records created by others to form an opinion on whether funds were diverted. At trial the defense objected that he lacked personal knowledge of the underlying transactions. The court permitted the testimony because expert opinions rest on specialized analysis rather than firsthand observation.
Ella Emerson offered an engineer's opinion that a manufacturing defect caused a product failure. The expert relied on general industry data but never tested the specific component at issue. The trial court excluded the testimony, finding too great a gap between the data and the conclusion offered.
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Edgar Evers, a software engineer, proposed to testify about the reliability of an algorithm used in a disputed transaction. The court applied the reliability framework to this technical testimony even though it was not traditional hard science. After considering the expert's methodology and its fit to the facts, the court admitted the opinion.
Enzo Eastwood's defense called a psychiatrist who examined the defendant and concluded that command hallucinations impaired his ability to make rational choices. The expert's opinion addressed the defendant's mental state at the time of the confession. The court considered the testimony in evaluating whether the statements were voluntary.
Elena Estrada's commitment proceeding featured a psychiatrist who testified that the patient's condition met the statutory criteria for involuntary hospitalization. The expert explained the diagnosis and the risk of harm using clinical observations and records. The court relied on the opinion to decide whether clear and convincing evidence supported commitment.
Edith Eberhardt's defense offered a psychologist to explain how lineup procedures and witness confidence can affect identification accuracy. The trial court evaluated whether the testimony would assist the jury on a disputed fact. After assessing relevance and reliability, the court admitted the expert opinion.
A party must disclose any witness it may use at trial to present scientific, technical, or other specialized opinion testimony, regardless of whether the witness is an outside consultant or a current employee. The disclosure must identify the witness as an opinion witness and, for non-reporting experts, include the subject matter and a summary of the facts and opinions.
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The disclosure must state the subject matter on which the physician is expected to present expert evidence and provide a summary of the facts and opinions to which the physician is expected to testify. A full written report is not required for non-reporting experts such as treating physicians.
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The court must sustain an objection to the undisclosed expert's testimony unless the failure was substantially justified or harmless. The duty to disclose is automatic and applies to any witness a party may use at trial to present opinion testimony based on specialized knowledge.
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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…