Learning Outcomes
After reading this article, you will be able to identify when evidence is relevant, recognize the main reasons relevant evidence may be excluded, and determine the proper scope of expert testimony under the Federal Rules of Evidence. You will be able to apply the Daubert standard, distinguish between lay and expert opinion, and answer MBE-style questions on these topics.
MBE Syllabus
For MBE, you are required to understand the principles of relevancy, exclusion of relevant evidence, and the rules governing expert testimony. This article covers:
- The definition of relevant evidence and the Rule 401/402 standard.
- The main reasons for excluding relevant evidence, including Rule 403 (unfair prejudice, confusion, waste of time).
- The requirements for admissibility of expert testimony under Rule 702 and the Daubert standard.
- The distinction between lay and expert opinion.
- The limits on the proper subject matter for expert testimony.
- The exclusion of expert testimony that invades the jury’s role or is otherwise inadmissible.
Test Your Knowledge
Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, remember to look more closely at that area during your revision.
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Which of the following is NOT a valid reason for excluding relevant evidence under Rule 403?
- (A) Unfair prejudice
- (B) Confusion of the issues
- (C) Lack of authentication
- (D) Undue delay
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Under the Federal Rules, expert testimony is admissible only if:
- (A) The expert is a licensed professional in the field.
- (B) The testimony will help the jury understand the evidence or determine a fact in issue.
- (C) The expert has previously testified in court.
- (D) The expert’s opinion is based solely on personal experience.
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Which standard governs the admissibility of scientific expert testimony in federal court?
- (A) Frye standard
- (B) Daubert standard
- (C) Best evidence rule
- (D) Confrontation Clause
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A lay witness may give opinion testimony if:
- (A) The opinion is based on scientific, technical, or specialized knowledge.
- (B) The opinion is rationally based on the witness’s perception and helpful to understanding the testimony.
- (C) The witness is an expert in the field.
- (D) The opinion concerns the ultimate issue in the case.
Introduction
Relevant evidence is generally admissible in court, but not all relevant evidence is allowed. The Federal Rules of Evidence set out when evidence is relevant, when it may be excluded despite being relevant, and what topics are proper for expert testimony. Understanding these rules is essential for answering MBE questions on evidence.
Relevancy: The Basic Standard
Evidence is relevant if it has any tendency to make a fact of consequence more or less probable than it would be without the evidence. This is a low threshold.
Key Term: Relevant Evidence
Evidence that has any tendency to make a fact of consequence more or less probable than it would be without the evidence.
Reasons for Excluding Relevant Evidence
Even if evidence is relevant, it may be excluded for policy or practical reasons. The most common basis is Rule 403, which allows exclusion if the probative value is substantially outweighed by dangers such as unfair prejudice, confusing the issues, misleading the jury, undue delay, wasting time, or needlessly presenting cumulative evidence.
Key Term: Rule 403 Exclusion
The court may exclude relevant evidence if its probative value is substantially outweighed by dangers like unfair prejudice, confusion, or waste of time.
Proper Subject Matter for Expert Testimony
Expert testimony is permitted only when specialized knowledge will help the trier of fact understand the evidence or determine a fact in issue. The expert must be qualified, the testimony must be based on sufficient facts or data, and the opinion must be the product of reliable principles and methods.
Key Term: Expert Testimony
Testimony by a qualified person with specialized knowledge that will help the jury understand the evidence or determine a fact in issue.Key Term: Daubert Standard
The standard for admitting expert scientific testimony, requiring the court to assess reliability and relevance based on factors such as testing, peer review, error rate, and general acceptance.
Lay Opinion vs. Expert Opinion
Lay witnesses may give opinions only if they are rationally based on the witness’s perception and helpful to understanding the testimony. Lay opinion cannot be based on scientific, technical, or specialized knowledge.
Key Term: Lay Opinion
Opinion testimony by a non-expert, limited to perceptions based on personal knowledge and not involving specialized knowledge.
Limits on Expert Testimony
Expert testimony is not permitted if it invades the jury’s role (e.g., stating a legal conclusion), is not helpful, or is not based on reliable methods. The court acts as a gatekeeper to ensure expert evidence meets the required standards.
Exclusion of Relevant Evidence: Rule 403
Rule 403 is the main mechanism for excluding relevant evidence. The court must weigh the probative value against the risk of unfair prejudice, confusion, misleading the jury, or wasting time. The exclusion is discretionary and rarely used unless the risk is substantial.
Worked Example 1.1
A plaintiff sues for injuries after a car accident. The defendant wants to introduce evidence that the plaintiff was previously convicted of shoplifting. The plaintiff objects.
Answer: The evidence is relevant only if it tends to prove a fact of consequence, such as the plaintiff’s credibility. However, under Rule 403, the court may exclude it if the risk of unfair prejudice (the jury disliking the plaintiff for being a shoplifter) substantially outweighs its probative value. Unless credibility is directly at issue, the court is likely to exclude the evidence.
Proper Subject Matter for Expert Testimony (Rule 702)
Expert testimony is admissible only if:
- The witness is qualified by knowledge, skill, experience, training, or education.
- The testimony will help the jury understand the evidence or determine a fact in issue.
- The testimony is based on sufficient facts or data.
- The opinion is the product of reliable principles and methods, and the expert has reliably applied those methods to the facts.
The Daubert standard requires the court to consider factors such as whether the theory or technique has been tested, subjected to peer review, has a known error rate, and is generally accepted in the field.
Worked Example 1.2
In a products liability case, the plaintiff offers an engineer to testify that a machine was defectively designed. The expert’s opinion is based on published studies, industry standards, and personal inspection.
Answer: The expert is qualified and the testimony is based on reliable methods and sufficient data. The testimony will help the jury understand technical issues, so it is admissible under Rule 702 and Daubert.
Exam Warning
The court will exclude expert testimony that simply tells the jury what result to reach or states a legal conclusion (e.g., “the defendant was negligent”). Expert testimony must assist, not replace, the jury’s decision-making.
Limits on Lay Opinion
Lay opinion is limited to perceptions based on the witness’s own senses and must not involve scientific or technical knowledge. Lay opinion is allowed for things like speed, appearance, or emotional state, but not for medical diagnoses or technical matters.
Worked Example 1.3
A witness testifies, “In my opinion, the driver was drunk.” The witness observed the driver’s slurred speech and unsteady walk.
Answer: This is permissible lay opinion because it is based on the witness’s perception and helps the jury understand the testimony. However, the witness could not testify, “The driver’s blood alcohol level was above the legal limit,” as this requires scientific knowledge.
Exclusion of Expert Testimony
Expert testimony may be excluded if:
- The expert is not qualified.
- The opinion is not based on sufficient facts or reliable methods.
- The testimony is not helpful to the jury.
- The opinion invades the jury’s role or states a legal conclusion.
Key Point Checklist
This article has covered the following key knowledge points:
- Relevant evidence is admissible unless excluded by a specific rule.
- Rule 403 allows exclusion of relevant evidence if the probative value is substantially outweighed by unfair prejudice, confusion, or waste of time.
- Expert testimony is admissible only if it meets the requirements of Rule 702 and the Daubert standard.
- Lay opinion is limited to perceptions based on personal knowledge and cannot involve specialized knowledge.
- Expert testimony must assist the jury and not state legal conclusions or invade the jury’s role.
Key Terms and Concepts
- Relevant Evidence
- Rule 403 Exclusion
- Expert Testimony
- Daubert Standard
- Lay Opinion
