One of the most common and vexing issues in evidence law concerns the intersection of lay and expert opinion testimony. When can a lay witness express an opinion under Federal Rule of Evidence (FRE) 701? When is an expert required under Rule 702? Can the same witness be used to give both fact and expert opinion testimony? These questions arise with great frequency in both criminal and civil litigation.
Determination of Testimony Type: Specialized Versus Particularized Knowledge
For the purpose of marking the line between lay and expert opinion testimony, the Federal Rules of Evidence and relevant Advisory Committee Notes (ACN) draw a distinction between “specialized” and “particularized” knowledge.
Expert witnesses have specialized knowledge. Expert testimony under Rule 702 is based on specialized training and education (i.e., Daubert evidence or specialized experience (i.e., Kumho Tire evidence). According to the ACN, the trial judge must find that any proffered expert evidence is “properly grounded, well reasoned, and not speculative” before admitting it. That is referred to as the court’s “gatekeeping” function.
Lay Witnesses have particularized knowledge. Lay opinion testimony is admissible under Rule 701 if it is (1) based on the witness’s own perceptions; (2) helpful to the trier of fact; and (3) not based on scientific, technical, or specialized knowledge. Classic examples of opinions that may be rendered by a lay witness include whether a person seemed angry, drunk, or scared; the distance, size, or weight of an object or person; and the relative speeds of vehicles on the road. The third Rule 701 stipulation is intended to prevent parties from subverting the expert disclosure requirements of Federal Rule of Civil Procedure 26 and Federal Rule of Criminal Procedure 16. If the proposed witness’s opinion is based on specialized knowledge or experience, then it can be admitted only as expert testimony under Rule 702.
In contrast to an expert witness, a lay witness possesses particularized knowledge as a result of experience. One common example arises in civil cases in which business losses are an element of damages. The business owner’s testimony about projected annual profits is proper lay opinion testimony. It is based on the owner’s knowledge of that particular business, not on any specialized training in accounting or economics. Similarly, a witness who is an experienced drug user may testify that the substance he inhaled at the defendant’s home was cocaine, based on particularized knowledge of the effects of cocaine. If the witness had never previously used drugs, or had used them only occasionally, he would not be allowed to give such testimony because he would lack the particularized knowledge on which to base an opinion. Furthermore, testimony that a substance recovered from the defendant’s home was cocaine hydrochloride, with a purity of 54 percent, could be given only by an expert who qualified under Rule 702.
Court Tests for Differentiating Expert and Lay Testimony
Courts have articulated different tests for determining whether an opinion is lay or expert.
One is called the “process of reasoning” test. A layperson may give an opinion when it results from “a process of reasoning familiar from everyday life.” State v. Brown, 836 S.W.2d 530, 549 (1992). An expert is required when the opinion results from “a process of reasoning which can be mastered only by specialists in the field.”
Some courts use a “vicarious knowledge” test, which focuses on how the witness learned the facts on which the opinion is based. Lay witnesses may testify only about facts of which they have personal knowledge. Experts usually rely, at least in part, on vicarious knowledge. One reason that the trial court is required to be a gatekeeper for expert testimony is that only experts may testify without firsthand knowledge of the facts underlying their opinions. It is an exception that could easily be abused if not closely monitored.
A recurrent issue in the case law concerns a situation in which a party proffers a witness who will testify as both a fact witness and an expert in the same case.
It is common for the government to offer such a witness in criminal cases. For example, the prosecution may present a narcotics officer as a fact witness about the events leading up to the defendant’s arrest and as an expert witness on the distribution of drugs. In a civil case involving corporations, a party may offer the chief financial officer as a fact witness and as an expert on proper accounting techniques.
The case law tends to be leery of such double duty. The court’s qualification of the witness as an expert can be seen by the jury as vouching for the witness’s credibility on the facts.
If your opponent notices an expert who will also testify to material facts in the case, you should object by means of an in limine motion. If you are the party who needs to present expert testimony, it is wiser strategy to offer it through a witness who will not also testify about the facts. Having two separate witnesses avoids a slew of pretrial motions that may result in a ruling excluding a key witness.
The line between lay and expert testimony is often a little blurry, but an understanding of not only court distinctions between specialized and particularized knowledge but also court tests to differentiate the two types of witnesses will help give some focus to the issue.
Cheryl D. Stein is a criminal defense lawyer in Washington, D.C.