AuthorGordon P. Cleary
Lay & Expert
§400 In General
§410 Lay Witness
§411 Collective Fact Opinion
§412 Skilled Lay Observer Testimony
§420 Experts
§421 Medical Experts
§422 Economic Experts
§423 Forensic Experts
§423.1 Technical Experts
§424 The Daubert Standard
§424.1 Daubert on Remand
§424.2 Daubert 
§424.3 Standard of Review on Daubert Rulings
§424.4 Daubert and Kumho Tire
§424.5 Daubert/Kumho Tire Motions Under Rule 702 Amendments
 
§426 Battered Woman Syndrome
§427 Battered Child Syndrome
§428 Rape Trauma Syndrome
§430 Practice Pointers
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4-3 LAY & EXPERT §410
§400 In General
In most jurisdictions and under the Federal Rules, both lay witnesses and expert witnesses are allowed to render
opinions. These opinions can range from a lay witness’ opinion as to the character of truthfulness of another witness
to opinions on the ultimate issue in a case rendered by experts. Before any opinion can be received into evidence,
however, a proper foundation must be laid for its admission. The following sections detail the foundational elements
for lay witness opinions and expert witness opinions, respectively.
§410 Lay Witness
At common law, only expert witnesses were allowed to express opinions. A lay witness was barred from giving
his opinion; rather, he was limited to testifying about things he perceived.
The common law eventually evolved. Many jurisdictions, as well as the Federal Rules of Evidence, now allow for
lay witness opinion testimony in certain circumstances. Generally, all that need be shown to have a lay witness express
an opinion is that the opinion is (a) rationally based on the perception of the witness and (b) helpful to either a clear
understanding of his testimony or the determination of a fact which is in issue.
A witness providing the lay opinion usually gives the jury a rather ordinary inference instead of recounting a series
of perceptions which would add up to the inference. For example, the witness might testify that a woman seemed sad
rather than testify about her facial expressions, body posture, tears, and so on.
The lay witness is still precluded from rendering an opinion beyond the realm of common experience. Those
opinions are left to experts. Furthermore, the lay witness may not give an opinion on a matter of law.
What constitutes expert testimony, or an opinion on a matter of law, is a legal determination which is to be made
by the judge. The weight which is to be given to the lay opinion, however, rests with the trier of fact.
The December 2000 amendments to Rule 701 make it clear where the line between opinions that may be rendered
by lay persons and those that may be rendered solely by experts is drawn. The amendment also is designed to prevent
circumvention of any pretrial disclosure requirements relating to expert witnesses. See Fed.R.Civ.P. 26(a)(2). Subdivi-
sion (A) of that rule requires the disclosure of “the identity of any person who may be used at trial to present evidence
under Rule 702, 703 or 705 of the Federal Rules of Evidence.”
Subdivision (B) of that rule also requires that a detailed written report be submitted from every “witness who is
retained or specially employed to provide expert testimony in the case or whose duties as an employee of the party
Rule 26 disclosure.
Prior to the amendments to Rule 701, however, the question was raised as to whether a lay witness with particular
expertise could testify under Rule 701 to what was essentially expert testimony while at the same time avoiding the dis-
closure requirements of Rule 26(a)(2). The amendment to Rule 701 ends this confusion by making clear that if a witness is
as a so-called “lay witness” as opposed to an “expert witness.” The amended language of the rule now states as follows:
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
Accordingly, under the amendment:
The test will be the subject matter of the testimony — i.e., 
When judged under 702 (as opposed to 701), the Fed.R.Civ.P. 26(a)(2) disclosure requirements must be met; and
The reliability requirements of Rule 702 also apply.
See amendments to Rule 702 codifying Daubert v. Merrill Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993) and
Kumho Tire Co. v. Carmichael, 526 U.S. 137, 119 S. Ct. 1167 (1999). See also, §420.

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