Is The Opinion “Lay” or “Expert?” — The Superior Court Has An Opinion (Maybe A Wrong One)

Lay opinion testimony is tolerated because, frankly, it is hard to find the line between fact and opinion (“she is tall,” “they appeared drunk,” “the car was way over the speed limit”) and because lay witnesses should be comfortable speaking in normal, conversational, easily-understood terms.  To ensure there is a foundation for the opinion rather than mere speculation, there is the testing device of cross-examination.

But lay witnesses may not cross a line and give testimony that is “based on scientific, technical, or other specialized knowledge within the scope of Rule 702.” Pa.R.Evid. 701.  That’s for experts, and with expert testimony comes discovery obligations such as reports and CVs.

The line is ill-defined.  And the language of 701 itself is blurry – when it says “specialized knowledge within the scope of Rule 702” does that mean that all specialized knowledge is within 702 or there are types of specialized knowledge, some covered by 702 and others not?  The answer is probably the latter, since some recognized forms of lay opinion have to be “specialized.”  When a witness says “Jules Epstein wrote that note” their claim is “specialized” to the extent that they, and not the jury, have “specialized” familiarity based on receiving mail from me or watching me write on the board in a lecture hall.

So where is that line?  In a split decision, the Superior Court found it proper to permit the following from a State Trooper investigating impaired driving:

Based on the totality of everything I saw, from [Appellant’s] driving, to my contact with him, to my testing with him, I was under the impression that he was not safe to drive a vehicle and that he was under the – he was being affected by some sort of illegal substance.

Commonwealth v. Nestor, 460 EDA 2023 (April 10, 2024).  The trooper added another factor, as described by the majority.  “Trooper Zimmerman opined that Appellant was impaired by a stimulant.”

There are really three opinions here:

  • Nestor was not safe to drive
  • Nestor was “affected by some sort of illegal substance”
  • Nestor had used and was impaired by “a stimulant”

Were this a test and we asked people to vote as to whether any is a lay opinion, I suspect that everyone would find the first opinion to be prototypic and unobjectionable but that the vote would be split on the latter two, with most concern being voiced about “stimulant.”  But to the Nestor majority, all three passed muster.

How did the Court get there?  In part by over-reading federal precedent; in part by misapprehending Federal Rule of Evidence 701; and in part by failing to address controlling Pennsylvania law.

Let’s start with the last, as it is closest to home.  The most significant decision seeking to draw the line between where lay opinion ends and expert opinion begins is Commonwealth v. Jones, 663 Pa. 20 (2020), a case unmentioned in Nestor.  In Jones the opinion witness was a Detective, the testimony was from “specialized” knowledge addressing how victims of sexual violence respond behaviorally and the Court found it improper to be offered as a lay witness.

Here, Detective Holzwarth primarily functioned as a fact witness but was also called upon to offer general opinion testimony concerning whether or not it was common for child victims of sexual assault to have trouble remembering dates and details of ongoing sexual assaults. Detective Holtzwarth was asked to provide insights gained through specialized occupational training and experience not within the average layperson’s knowledge base as required by the plain language of Rule 702(a). Detective Holzwarth called upon the wealth of his knowledge and training as a detective with extensive experience investigating sexual assaults and made connections for the jury based on that specialized knowledge…

Accordingly, we hold that testimony from a law enforcement officer concerning child victims’ typical behaviors and responses to sexual abuse, when based on that officer’s training and experience, falls within the realm of expert testimony.

Jones, 663 Pa. at 36.  It is hard to find a difference between the Detective’s testimony and that of the trooper in Nestor.

The second error is in over-reading federal precedent in analyzing specialized knowledge lay opinion testimony.  Here is what the Nestor majority wrote:

As the Third Circuit has stated, “the reliability of lay opinion testimony should be assessed in light of the witness’s relevant specialized knowledge and experience.” United States v. Savage, 970 F.3d 217, 286 (3d Cir. 2020). Further, in distinguishing between specialized lay witness testimony under F.R.E. 701 and expert testimony under F.R.E. 702, the Savage Court noted:

[w]hen a lay witness has particularized knowledge by virtue of her experience, she may testify—even if the subject matter is specialized or technical—because the testimony is based on the layperson’s personal knowledge rather than on specialized knowledge within the scope of Rule 702. Thus, as long as the technical components of the testimony are based on the lay witness’s personal knowledge, such testimony is usually permissible under Rule 701.

Id. (quoting United States v. Fulton, 837 F.3d 281, 301 (3d Cir. 2016)) (emphasis added; footnote, paragraph break and quotation marks omitted).

Commonwealth v. Nestor, 2024 Pa. Super. LEXIS 130, *12.  What is omitted is the type of personal experience Savage was addressing – an Agent testifying as to the meaning of coded words in drug or gang transactions.  Why is that different?  Because that knowledge is gained directly in the undercover investigation and thus personally experienced and closer to factual testimony.

The final error is the broader misapprehension of  FRE 701, which the Nestor majority looks to for guidance.  When amended in 2000 to make clear that expert opinions could not be introduced as lay opinion, the Comment included the following:

The amendment incorporates the distinctions set forth in State v. Brown, 836 S.W.2d 530, 549 (1992), a case involving former Tennessee Rule of Evidence 701, a rule that precluded lay witness testimony based on “special knowledge.” In Brown, the court declared that the distinction between lay and expert witness testimony is that lay testimony “results from a process of reasoning familiar in everyday life,” while expert testimony “results from a process of reasoning which can be mastered only by specialists in the field.”

Rule 701. F.R.Evid., Committee Notes on Rules – 2000 Amendment,


Although a lay witness must rely on a generalization resting exclusively or primarily on his or her personal knowledge, an expert witness is likely to draw on a wide range of sources, including much hearsay–lectures by his [or her] teachers, statements in textbooks, reports of experiments and experiences of others in the same field.  In other words, in formulating the generalization, the expert relies on vicarious as well as personal experience.

68 SMU L. Rev. at 88-89 (internal quotations and footnotes omitted).  In other words, where the witness relies on anything more than direct hands-on exposure and has to reason from external sources of knowledge, that puts the witness into the expert category.

There are real concerns about allowing a purported lay witness to give what is expert opinion testimony.  As explained by Professor Jason Chin and colleagues, “[t]he first hazard is unconscious bias and the fact that lay witnesses need not demonstrate they relied on a methodology to control that bias. A lack of methodology would not be so problematic if not for the second hazard, a specious nexus between the witness’s authority and his or her evidence…”  Chin, Tomiska and Li, DRAWING THE LINE BETWEEN LAY AND EXPERT OPINION EVIDENCE, 63 McGill L.J. 89, 105 (2017).

Where does the trooper in Nestor fit?  The trooper testified to training received in the academy, and, once on the force, in “ARIDE tests, Advanced Roadside Impaired Driving Enforcement” which includes “instruction about common drugs that are used and abused, indicators that different drugs can show.” The trooper then claimed that “my job brings me around lots of different situations with impaired people. In my  experience, the way he was acting is the way that someone that’s impaired by some sort of stimulant acts.”

So what is wrong here?  First, the training and the exposure seem inseparable; and, second, there is no elaboration of the purported claim of first-hand exposure – how many instances and how the officer confirmed the suspects were using stimulants.  Perhaps most importantly, if the exposure to people on stimulants was obtained ‘on the job,’ that should still be considered expert testimony.

Why? Because under both the Federal and Pennsylvania rules, if the specialized knowledge is “beyond that possessed by the average layperson” [the Pennsylvania formulation] or “will help the trier of fact to understand the evidence or to determine a fact in issue[,]” [the Federal test], the person must be an expert to provide it.  That is the case here.

Absent a conclusive showing that what the Trooper said was based solely on personal exposure/events and with no reliance on training or on-the-job experience, the testimony should have been viewed as expert.  As importantly, the Superior Court majority should have recognized and articulated the difference.


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