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Lay Witness vs. Expert Witness Opinions: A Primer

At common law, lay witnesses could testify to facts, but unlike experts, could not offer opinions, inferences, or conclusions.

Anjelica Cappellino, J.D.

Written by
— Updated on April 11, 2022

Lay Witness vs. Expert Witness Opinions: A Primer

The justification was that unless the information was too complex for a jury to understand without the help of an expert, a jury should be able to interpret evidence and draw its own conclusions.

However, as the Supreme Court has noted, there is an “inevitably arbitrary line between the various shades of fact/opinion”. Once Rule 701 of the Federal Rules of Evidence was enacted, the restrictions on lay opinions began to loosen. Now, both lay and expert opinions are admissible at trial, to varying degrees. In order to ensure that your expert testimony is utilized to its full potential, it is important to note the differences between the two types of witnesses so that both can offer admissible opinions.

How Do Lay Opinions Differ from Expert Opinions?

Lay opinion testimony is largely defined by what it is not—expert testimony. Under Rule 702, a witness who is qualified as an expert by knowledge, skill, experience, training, or education may testify in the form of an opinion or otherwise if:

(a) the expert’s scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue;
(b) the testimony is based on sufficient facts or data;
(c) the testimony is the product of reliable principles and methods; and
(d) the expert has reliably applied the principles and methods to the facts of the case

In contrast, Rule 701 of the Federal Rules of Evidence states that if a witness is not testifying as an expert, testimony in the form of an opinion is limited to one that is:

(a) rationally based on the witness’s perception;
(b) helpful to clearly understanding the witness’s testimony or to determining a fact in issue; and
(c) not based on scientific, technical, or other specialized knowledge within the scope of Rule 702

Personal Knowledge is Required

The major difference between these two types of witnesses is personal knowledge. While experts may use their knowledge or skill to draw conclusions, lay witnesses can only base their opinions on information they personally observed.

Rule 602 of the Federal Rules of Evidence requires that a witness may only testify if evidence is sufficient to support a finding that the witness has personal knowledge of the matter. Rule 602 specifically exempts expert testimony from this requirement. In comparison, Rule 703 allows experts to rely upon facts and data beyond what they have personally observed. Rather, experts can consider facts that would otherwise be inadmissible, so long as experts in their particular field would reasonably rely on such information.

Lay witnesses, however, are constrained by relying on information they have gained through personal knowledge and rationally based perception. Of course, what constitutes personal knowledge can be quite broad, as lay witnesses can and do testify to an array of various matters. Generally, courts have held that observation of an event or situation clearly falls within the definition of personal knowledge. Whether as a first-hand witness to a car accident or crime, lay opinions may be rendered about what the witness observed.

Courts have also held that lay witnesses may testify to their perception of the incident if obtained through earlier personal observations. The opinions that lay witnesses have been permitted to testify about vary widely throughout jurisdictions. Lay witnesses can offer opinions relating to degrees of light, sound, weight, and distance, as well as a person’s appearance, identity, or manner of conduct. In addition, lay witnesses’ perceptions must be rationally based. However, the standard of rational perception is not rigorous. Witnesses are only required to use their everyday logic to reach their conclusion.

Similar to Rule 702’s requirements for expert testimony, lay witness testimony must be helpful to the fact-finder. Unlike an expert offering his own scientific, technical, or other specialized knowledge to assist the jury with complex issues, lay opinion testimony is usually considered helpful when the witness is in a better position than the jury to form an opinion and the facts alone would be inadequate to provide a complete understanding of the testimony.

Lastly, lay opinions cannot be based on scientific, technical, or other specialized knowledge within the scope of Rule 702. Therefore, lay opinions must be wholly independent of expert testimony. As an extension of this rule, lay witnesses generally cannot answer hypothetical questions, as all of their opinions must be based on facts they personally observed.

Disclosure Rules

Whether one’s testimony is categorized as lay opinion or expert opinion is important to determine well before the commencement of trial. The type of witness a party intends to call to the stand can greatly affect its disclosure obligations. Generally, there are more discovery requirements for expert witnesses than lay witnesses.

Under Rule 26 of the Federal Rules of Civil Procedure, expert witnesses must disclose to the opposing party a report previewing the expert’s proposed testimony. The report must be sufficiently detailed and contain “all opinions the witness will express and the basis and reasons for them”.

Rule 26(a)(2)(B) also mandates disclosure of facts or data considered by the witness, any exhibits the expert intends to use, the witness’ qualifications, a list of other cases in which the witness testified, and a statement regarding the expert’s compensation for testifying. If the expert fails to timely file the report, the trial judgment can bar any and all of the expert’s testimony.

Rule 16 of the Federal Rules of Criminal Procedure has fashioned a similar requirement for expert witnesses. In contrast, there are no such requirements for lay opinion witnesses.

Expert Scrutiny

In addition, expert testimony may be subjected to heightened judicial scrutiny. Prior to trial, an adversary may request a Daubert hearing where the party seeking to admit the expert must establish the reliability of the testimony. If the court concludes that the expert’s testimony is based on questionable methodology, the entire testimony can be excluded. Once trial commences, expert witnesses must also overcome voir dire questioning by both parties to prove to the court that they possess the requisite qualifications in their respective fields of study.

Overall, experts are afforded the opportunity to testify to a wider latitude of opinion in comparison to lay witnesses. They are also subjected to stricter scrutiny in terms of disclosure and evidentiary rules. If lay and expert witnesses are utilized at trial, it is important to be cognizant of the particular rules governing each, so that both witnesses can offer testimony effectively.

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