Also known as: testifying expert · expert witness
Written by attorneys · grounded in primary & secondary sources — see below
An expert retained by a party to offer opinion testimony at trial on matters requiring specialized knowledge that will assist the trier of fact.
Trevor Tate faced federal fraud charges. The prosecution called an accountant as a testifying expert who reviewed ledgers and then stated that Tate had formed the specific intent to defraud investors. The court struck that portion of the testimony because the expert could not opine on the mental-state element reserved for the jury.
Taliah Tang was prosecuted for sexual assault. The state called a forensic analyst as a testifying expert who relied on a DNA profile generated by an out-of-state lab to form her independent opinion that the sample matched the defendant. The court admitted the testimony after finding the profile served only as the basis for the expert's conclusion and was not offered for its truth.
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Timothy Tang sued a drug manufacturer alleging a defective warning label. Defense counsel cross-examined the plaintiff's pharmacologist testifying expert by directing her to a specific passage in a medical treatise. The expert acknowledged the passage as reliable authority, and the court permitted counsel to read the statement into the record.
Tyrone Tran was tried for murder. The defense offered a psychologist as a testifying expert who proposed to introduce results from a new systolic-blood-pressure deception test. The court excluded the testimony after finding the underlying method had not gained general acceptance in the scientific community.
Tabitha Taylor sued an auto maker in State A for a defective seat-belt design. She designated a Michigan engineer as a testifying expert who had never examined the actual vehicle. The court permitted the expert to testify after confirming that his opinions rested on data and methods that satisfied the reliability standards applicable in the forum.
Thomas Thompson sued a chemical company claiming exposure caused his illness. He offered an epidemiologist as a testifying expert whose opinion rested on studies that did not address the precise exposure levels at issue. The court excluded the testimony, holding that the analytical gap between the data and the expert's conclusion rendered the opinion unreliable.
A testifying expert is retained to provide opinion testimony at trial and must satisfy disclosure, qualification, and reliability requirements. A consulting expert assists counsel but does not testify and generally remains protected from discovery.
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No. In a criminal case an expert may not state an opinion on whether the defendant possessed a mental state that constitutes an element of the crime or a defense. That determination belongs to the trier of fact alone.
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A testifying expert may rely on such data when the out-of-court report is used only to explain the basis of the expert's independent opinion and is not offered for its truth, provided the report was not prepared primarily to accuse a targeted individual.
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A party must disclose the expert's identity, a written report containing the opinions and their bases, the facts or data considered, exhibits, qualifications, prior testimony, and compensation, and must supplement that information as required.
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On a party's motion or on its own initiative, the court may order the parties to show cause why a neutral expert should not be appointed when technical disputes between party experts create difficulty that independent assistance would resolve.
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…Center conceded liability for the lost transparencies and the issue of damages was tried before a jury. At trial, Gasperini's expert witness testified that the "industry standard" within the photographic publishing community valued a lost transparency at $1,500. See id. , at 227. This industry standard, the expert explained,…