Also known as: expert witnesses
Written by attorneys · grounded in primary & secondary sources — see below
A person qualified by specialized knowledge, skill, experience, training, or education whose opinion testimony assists the trier of fact in understanding evidence or determining a fact in issue. The testimony must rest on sufficient facts or data, employ reliable principles and methods, and reflect a reliable application of those principles and methods to the facts of the case.
In a federal mail-fraud prosecution, the government calls a forensic accountant to explain the charity's ledgers. On direct examination the accountant states that the timing of transfers shows the defendant fully intended to deprive donors of restricted funds. The court sustains the defense objection and strikes the testimony because the opinion directly addresses an element of the charged offense.
A state DNA analyst testifies that a crime-scene profile matches the defendant's profile generated by her own laboratory. She explains that she compared her results to a profile produced by an out-of-state lab and reached an independent conclusion. The court admits the testimony over a confrontation objection because the out-of-state report was used only to show the basis of the analyst's opinion and was not offered for its truth.
Select any source to read its text and confirm it supports the definition.
In a class action alleging misrepresented cellular coverage, the parties' engineers present conflicting throughput measurements. The district judge, on its own initiative, orders the parties to show cause why a neutral specialist should not be appointed. After the parties submit nominations, the court selects a qualified engineer who consents to serve and directs the expert to advise the parties of all findings.
An aerospace engineer retained by the plaintiff testifies about orbital-stability tolerances. Defense counsel hands the witness a chapter from a recognized engineering treatise and asks whether the author states that certain inspection routines are industry standard. The witness acknowledges the statement. The court permits counsel to read the passage into evidence but refuses to admit the treatise itself as an exhibit.
A plaintiff offers a tire-failure analyst who concludes that a manufacturing defect caused the blowout. The defendant moves to exclude the testimony, arguing that the analyst's visual-inspection method lacks tested reliability. The court conducts a pretrial hearing, finds the methodology unreliable under the governing standard for all expert testimony, and excludes the opinion.
A defendant charged with shooting his wife claims he acted during a confusional arousal and lacked awareness or intent. The trial court, over objection, appoints a psychiatrist to examine the defendant and testify at trial. The expert later testifies about the defendant's mental condition. The court instructs the jury that the expert was appointed because the defense raised an insanity claim.
Yes. On a party's motion or on its own initiative, the court may order the parties to show cause why an expert should not be appointed and may select any qualified expert who consents to serve, including one of the court's own choosing.
In a criminal case an expert may not state an opinion on whether the defendant possessed a mental state or condition that constitutes an element of the crime or a defense. Those questions remain exclusively for the trier of fact.
An expert may rely on such a report to explain the basis of an independent opinion when the report is not offered for its truth and was not prepared primarily to accuse a targeted individual. The Confrontation Clause is not violated under those circumstances.
A statement from a treatise, periodical, or pamphlet may be read into evidence if called to the expert's attention on cross-examination or relied upon by the expert on direct examination, provided the publication is established as a reliable authority.
…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,…