Also known as: expert opinions · expert testimony · opinion testimony · expert witness testimony · Rule 702 testimony
Written by attorneys · grounded in primary & secondary sources — see below
Opinion testimony by a witness qualified through knowledge, skill, experience, training, or education on a subject requiring scientific, technical, or other specialized knowledge. The testimony must be relevant and rest on reliable principles and methods applied reliably to the facts of the case. Courts serve as gatekeepers to exclude opinions lacking sufficient factual support or a reliable methodology.
Esther Eisenberg, a forensic engineer, testified that a manufacturing defect caused a machine failure even though she had not observed the machine in operation. The court admitted her opinion because the personal knowledge requirement of Rule 602 does not apply to expert testimony. Her conclusions rested on data of the type reasonably relied upon by engineers in the field.
Ethan Evans offered expert testimony that a chemical exposure caused the plaintiff's illness based solely on animal studies never validated in humans. The district court excluded the opinion after finding the methodology untested and lacking peer review or known error rates. The gatekeeping function required exclusion of the unreliable evidence.
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Edgar Evers, a toxicologist, concluded that a defendant's product caused the plaintiff's specific symptoms, yet the underlying studies addressed only general causation. The court found too great an analytical gap between the data and the proffered opinion. It therefore excluded the testimony on reliability grounds.
Elena Estrada, an automotive engineer, testified that a tire design was defective based on specialized technical analysis. The court applied the flexible reliability inquiry to the engineering testimony rather than limiting review to scientific methods alone. It admitted the opinion after confirming appropriate standards and controls.
Enzo Eastwood sought to introduce expert testimony on a novel lie-detection technique. The court required the proponent to show the method enjoyed general acceptance in the relevant scientific community. Because the technique lacked such acceptance, the testimony was excluded.
Emmett Egan presented expert economic analysis to quantify the ratio of punitive to compensatory damages in an insurance bad-faith case. The court considered the expert's methodology to ensure the ratio remained within constitutional bounds. The testimony helped the jury evaluate the appropriate amount without producing an arbitrary award.
The witness must demonstrate knowledge, skill, experience, training, or education sufficient to assist the trier of fact on the subject. Qualification is assessed relative to the specific issues in the case rather than requiring formal academic credentials in every instance.
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Courts evaluate factors including whether the theory has been tested, subjected to peer review, possesses a known error rate, maintains controlling standards, and enjoys general acceptance. The inquiry remains flexible and case-specific rather than applying a rigid checklist.
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Appellate courts review the decision for abuse of discretion. The trial court's gatekeeping determination receives substantial deference provided the court adequately assesses both relevance and reliability.
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Yes. An expert may rely on facts made known at trial, supplied through hypothetical questions, or drawn from materials of a type reasonably relied upon by experts in the field even without personal observation.
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…B. Deus ex Machina The Supreme Court's opinion in Daubert focuses closely on the language of Fed.R.Evid. 702, which permits opinion testimony by experts as to matters amounting to "scientific ... knowledge." The Court recognized, however, that knowledge in this context does not mean absolute certainty. --- U.S. at ----, 113 S.Ct.…