Learning Outcomes
After reading this article, you will be able to identify when expert testimony is relevant, explain the main reasons relevant expert evidence may be excluded, and apply the Daubert reliability standard. You will also be able to distinguish between lay and expert opinion, recognize the requirements for expert qualification, and answer MBE-style questions on this topic.
MBE Syllabus
For the MBE, you are required to understand the rules governing the admissibility of expert testimony and the exclusion of otherwise relevant evidence. This includes:
- Recognizing when expert testimony is relevant and necessary.
- Identifying the foundational requirements for expert opinion evidence.
- Applying the Daubert standard for reliability.
- Distinguishing between lay and expert opinion.
- Understanding reasons for excluding relevant expert evidence (e.g., unfair prejudice, confusion, waste of time).
- Knowing the judge’s gatekeeping role in admitting expert testimony.
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 required element for admissibility of expert testimony?
- The expert is qualified by knowledge, skill, experience, training, or education.
- The expert’s opinion is based on sufficient facts or data.
- The expert’s opinion is based solely on personal belief.
- The expert’s methods are reliably applied to the facts.
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Under the Daubert standard, which factor is LEAST relevant to determining the reliability of expert testimony?
- Whether the theory has been tested.
- Whether the theory is generally accepted in the field.
- Whether the expert is a friend of the judge.
- Whether the error rate is known.
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A relevant expert opinion may be excluded if:
- It is based on reliable methods.
- Its probative value is substantially outweighed by the danger of unfair prejudice.
- The expert is qualified.
- The testimony is helpful to the jury.
Introduction
Expert testimony is often essential in cases involving technical, scientific, or specialized knowledge. However, not all relevant expert evidence is admissible. The Federal Rules of Evidence and MBE require you to know when expert opinion is relevant, what foundational requirements must be met, and why relevant expert evidence may still be excluded.
Relevance and the Role of Expert Testimony
Expert testimony is relevant if it helps the trier of fact understand evidence or determine a fact in issue. Unlike lay opinion, expert opinion can address matters beyond common experience.
Key Term: Expert Testimony Opinion evidence given by a witness qualified as an expert, based on specialized knowledge, skill, experience, training, or education, that assists the trier of fact in understanding evidence or determining a fact in issue.
Foundational Requirements for Expert Testimony
For expert testimony to be admissible, the following must be satisfied:
- The witness is qualified as an expert.
- The testimony will help the trier of fact.
- The opinion is based on sufficient facts or data.
- The opinion is the product of reliable principles and methods.
- The expert has reliably applied those principles and methods to the facts.
Key Term: Daubert Standard The standard used by courts to assess the reliability and relevance of expert testimony, considering factors such as testability, peer review, error rate, and general acceptance in the field.
The Daubert Reliability Standard
The judge acts as a gatekeeper, ensuring that expert evidence is not only relevant but also reliable. Under Daubert, reliability is assessed by considering:
- Whether the theory or technique can be and has been tested.
- Whether it has been subjected to peer review and publication.
- The known or potential error rate.
- The existence and maintenance of standards.
- Whether the method is generally accepted in the relevant field.
Reasons for Excluding Relevant Expert Evidence
Even if expert testimony is relevant and meets foundational requirements, it may still be excluded under Rule 403 if its probative value is substantially outweighed by dangers such as:
- Unfair prejudice.
- Confusing the issues.
- Misleading the jury.
- Undue delay, waste of time, or needless presentation of cumulative evidence.
Key Term: Rule 403 Exclusion The court’s authority to exclude relevant evidence if its probative value is substantially outweighed by the risk of unfair prejudice, confusion, or waste of time.
Lay Opinion vs. Expert Opinion
Lay witnesses may give opinions only if they are rationally based on their perception and helpful to understanding their testimony. Expert witnesses may give opinions based on specialized knowledge and may rely on facts not personally observed if reasonably relied upon by experts in the field.
Key Term: Lay Opinion Testimony by a non-expert witness limited to opinions based on firsthand perception and helpful to understanding the witness’s testimony or determining a fact in issue.
Judge’s Gatekeeping Role
The trial judge must determine whether the expert’s testimony is both relevant and reliable before it is presented to the jury. This includes evaluating the expert’s qualifications and the reliability of the methods used.
Worked Example 1.1
A plaintiff sues a car manufacturer, alleging a design defect caused a crash. The plaintiff offers an engineer as an expert. The engineer’s opinion is based on a method not generally accepted in automotive engineering, has never been peer-reviewed, and has an unknown error rate. The manufacturer objects.
Answer: The judge should exclude the expert’s opinion. Under the Daubert standard, the method’s lack of general acceptance, absence of peer review, and unknown error rate indicate it is not reliable. The judge, as gatekeeper, must ensure only reliable expert evidence is admitted.
Worked Example 1.2
A medical expert is called to testify that a certain drug caused the plaintiff’s injury. The expert is qualified and the testimony is relevant, but the expert’s opinion is based on a single case report and personal belief, not on scientific studies or accepted methodology.
Answer: The court should exclude the testimony. Expert opinions must be based on sufficient facts or data and reliable methods, not just personal belief or anecdote.
Exam Warning
The MBE may test whether expert evidence is excludable even if it is relevant and the expert is qualified. Always consider Rule 403 and the Daubert reliability factors.
Revision Tip
When answering MBE questions on expert testimony, always check if the expert’s opinion is both relevant and reliable. If the method is novel or controversial, apply the Daubert factors.
Key Point Checklist
This article has covered the following key knowledge points:
- Expert testimony must be relevant and assist the trier of fact.
- The expert must be qualified and use reliable methods (Daubert standard).
- The judge acts as gatekeeper for reliability and relevance.
- Relevant expert evidence may be excluded under Rule 403 (unfair prejudice, confusion, waste of time).
- Lay opinion is limited to firsthand perceptions; expert opinion is based on specialized knowledge.
- Expert opinions must be based on sufficient facts or data, not just personal belief.
Key Terms and Concepts
- Expert Testimony
- Daubert Standard
- Rule 403 Exclusion
- Lay Opinion
