Opinion Testimony and Expert Evidence: every key term you need (+ practice quiz)
25 flashcard terms for Evidence Topic 4, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 15-question quiz — free, no account needed.
Opinion testimony by a witness who is not testifying as an expert, admissible only if rationally based on the witness's own perception, helpful to the trier of fact, and not resting on specialized knowledge governed by FRE 702.
Rational basis requirement (lay opinion)
The FRE 701 condition that a lay opinion grow out of firsthand perception by the witness. A witness who did not observe the underlying facts, or who reasons from technical training, cannot satisfy this prong.
Helpfulness prong of FRE 701
A lay opinion must aid the jury in understanding testimony or deciding a fact. Shorthand descriptions such as speed, intoxication, sanity, identity, or emotional state are classic examples of helpful lay conclusions.
FRE 701(c) anti-evasion clause
Added in 2000 to stop parties from smuggling expert opinion in through a lay witness and thereby dodging reliability screening and expert disclosure duties. Any specialized-knowledge opinion must proceed under FRE 702.
Lay-expert hybrid witness
A witness such as a treating physician or a business owner who may give some testimony from personal perception and other testimony only if qualified as an expert. Courts require the proponent to separate the two tracks.
Expert qualification under FRE 702
A witness may be qualified as an expert by knowledge, skill, experience, training, or education. Formal credentials are not required, and a strong resume alone does not guarantee that a given opinion is reliable.
Helpfulness standard for expert testimony
The threshold FRE 702 requirement that the expert's scientific, technical, or other specialized knowledge help the trier of fact understand the evidence or determine a fact in issue. Testimony on obvious matters fails this test.
Sufficient facts or data (FRE 702)
The reliability element requiring an adequate factual foundation for the opinion. A conclusion drawn from too small a sample, cherry-picked studies, or unverified assumptions may be excluded even if the method itself is sound.
Reliable principles and methods
The FRE 702 element focused on the soundness of the expert's methodology rather than the correctness of the ultimate conclusion. The inquiry is whether the technique has the hallmarks of intellectual rigor in the field.
Reliable application to the facts
The FRE 702 element asking whether the expert applied a sound method faithfully to the particular facts of the case. A valid method executed carelessly or selectively yields an inadmissible opinion.
Daubert v. Merrell Dow Pharmaceuticals
The 1993 decision holding that the Federal Rules superseded Frye and assigning trial judges a gatekeeping duty to screen scientific testimony for evidentiary reliability and fit with the issues in the case.
Daubert reliability factors
Nonexclusive considerations for scientific validity: whether the theory can be and has been tested, peer review and publication, known or potential error rate, existence of standards controlling operation, and general acceptance.
Testability and falsifiability factor
The Daubert consideration asking whether the expert's theory has been subjected to empirical testing capable of proving it wrong. An untestable claim is philosophy or speculation rather than science for admissibility purposes.
Known or potential error rate
The Daubert factor examining how often a technique produces false results and whether that rate has been measured. Techniques with unmeasured or undisclosed error rates draw heightened judicial skepticism.
Frye general acceptance test
The 1923 standard admitting scientific evidence only if the underlying principle had gained general acceptance in the relevant scientific community. Displaced in federal court by Daubert but retained by several states.
Judicial gatekeeping function
The trial court's obligation to determine under FRE 104(a) whether proffered expert testimony is qualified, reliable, and helpful before the jury hears it, screening out unsupported opinion rather than leaving all of it to cross-examination.
General Electric Co. v. Joiner
The 1997 decision holding that appellate courts review admissibility rulings on expert testimony only for abuse of discretion, and that a judge may exclude an opinion connected to the data only by the expert's own say-so.
Analytical gap doctrine
The Joiner principle that a court may exclude testimony when too great a distance separates the studies relied on from the conclusion offered. The gap, not the credentials, is the ground of exclusion.
Kumho Tire Co. v. Carmichael
The 1999 decision extending the gatekeeping obligation beyond science to technical and experience-based expertise, while giving trial courts flexibility to choose which reliability factors fit the discipline at issue.
Experience-based expert testimony
Opinion grounded in practical skill rather than published science, such as accident reconstruction or handwriting comparison. After Kumho Tire the proponent must explain how the experience reliably supports the specific conclusion.
2023 amendment to FRE 702
A clarifying revision emphasizing that the proponent must establish each admissibility requirement by a preponderance of the evidence and that the expert's opinion must reflect a reliable application of the method to the case facts.
Overstatement of expert conclusions
The problem the 2023 amendment targets when an expert claims a degree of certainty the underlying method cannot support, such as declaring a categorical identification from a technique with an unquantified error rate.
FRE 703 bases of expert opinion
An expert may rely on facts perceived, learned at the hearing, or made known outside the record if experts in the field reasonably rely on such material, even when that material is itself inadmissible.
Reverse balancing test of FRE 703
Inadmissible basis material may be disclosed to the jury only if its probative value in helping evaluate the opinion substantially outweighs its prejudicial effect, a test that tilts against disclosure unlike ordinary FRE 403.
Ultimate issue rule and FRE 704(b)
FRE 704 abolishes the general bar on opinions embracing an ultimate issue, but subsection (b) forbids an expert in a criminal case from stating whether the defendant had the mental state constituting an element or a defense.