Pennsylvania remains a Frye jurisdiction, with the threshold for expert discipline evidence being whether it has "general acceptance." The goal is to let the specialists—those in the discipline who presumably know best—tell the courts what is reliable; and once that is resolved the issue is not to be revisited. Or so it has seemed, and so it has been posited. But two cases—one awaiting decision in the Pennsylvania Supreme Court and another recently issued by the Superior Court—call into question the conventional wisdom of how Frye issues are to be addressed in this commonwealth.

First, some background. Pennsylvania accepted Frye 42 years ago, in Commonwealth v. Topa, 471 Pa. 223, 369 A.2d 1277 (Pa. 1977). Quoting federal law, the Topa court emphasized the relative role of judges and scientists, explaining that with Frye "those most qualified to assess the general validity of a scientific method will have the determinative voice." The role of judges seemed deferential: "Frye contemplated a judicial inquiry, informed by experts, into the general acceptance of the scientific methods used," see Walsh v. BASF, 191 A.3d 838, 843 (Pa.Super. 2018).

Beyond limiting the role of the judge to confirming that the relevant field "generally" accepted the methodology, a second limitation was imposed. Once a court had approved a discipline as generally accepted, no further Frye inquiry would be tolerated. The Frye determination was to be limited to "novel" science or techniques. As the Pennsylvania Supreme Court emphasized in 2008, "Frye is not implicated every time science comes into the courtroom; rather, it applies only to proffered expert testimony involving novel science," as in Commonwealth v. Puksar, 597 Pa. 240, 253, 951 A.2d 267, 275 (Pa. 2008) (internal quotations omitted). This established a sense of "permanency."

A third principle also was made manifest. Any Frye inquiry was to be limited to whether the methodology was generally accepted, and not whether the resulting conclusion was. "Assuming the expert is properly qualified to testify … his expertise, appropriately brought to bear on the issue through use of generally accepted scientific principles and methodology, should also pass muster under Frye," as in Trach v. Fellin, 817 A.2d 1102, 1114 (Pa.Super. 2003).

These seemingly inviolate principles have eroded over time. In 2012, the court determined that "a reasonably broad meaning should be ascribed to the term 'novel.'" A Frye determination could now occur when there are "articulable grounds to believe that an expert witness has not applied accepted scientific methodology in a conventional fashion in reaching his or her conclusions." See Betz v. Pneumo Abex, 615 Pa. 504, 545-546, 44 A.3d 27, 53 (Pa. 2012). See also, Commonwealth v. Jacoby, 642 Pa. 623, 667, 170 A.3d 1065, 1091 (Pa.  2017) (same).

It has also been acknowledged, albeit at times indirectly, that atop of any 702/Frye analysis a court may independently assess the proffered expert testimony under Rule 403, reviewing it for whether it is misleading, confusing or unfairly prejudicial. See, e.g., Commonwealth v. Brown, 2019 Pa. Super. Unpub. LEXIS 2840, *11 (July 25, 2019) (conducting a 403 analysis after determining the proof satisfied Frye and Rule 702). This is a more contentious claim, as the Supreme Court has emphasized that "in the context of the more conventional realms of science, the Pennsylvania decisions tend to downplay the courts' screening function. A manifestation of this trend is that challenges generally are vetted through the Frye litmus …"

Finally, the court has expressly acknowledged that a science or discipline, no longer novel, may be subject to re-examination if questions arise as to whether it is now generally accepted. "We do not discredit the notion … that a once-viable science may lose its wide acceptance in the scientific community and may be challenged pursuant to Rule 702," see Commonwealth v. Chmiel, 612 Pa. 333, 386, 30 A.3d 1111, 1142 Pa. 2011).

This last point, that Frye is not forever, is at the core of a recent, unpublished, Superior Court decision. In Commonwealth v. Ross, a capital murder defendant challenged the admissibility of bitemark evidence. The trial judge declined to hold a Frye hearing, as such evidence was no longer "novel." An interlocutory appeal was not allowed by the Superior Court, but the Supreme Court remanded with a directive that the appeal be heard.

On that appeal decided on Nov. 21, the Superior Court first confirmed that Ross had produced evidence of a "lack of consensus" among forensic odontologists. From this a second conclusion flowed—there were "articulable grounds that the commonwealth's expert witnesses on bite mark identification analysis have not applied accepted scientific methodology in reaching their conclusions." See Commonwealth v. Ross, 2019 Pa. Super. Unpub. LEXIS 4359, *18 (Pa. Super. Ct. Nov.21, 2019). In plainer language, if there is no general acceptance there is no scientific methodology.

The Superior Court took an even more important, and rarely undertaken, analytical step. Rather than let the field be defined solely by its practitioners, the appellate court acknowledged that more than dentists make up the relevant community. "Bite mark identification analysis not only involves concepts relating to forensic science generally, but also pathology, biology, statistics, and metrology." Once it is recognized that the field might be broader, the test for general acceptance becomes more stringent.

Ross makes clear that Frye is not forever, and what was once readily accepted may subsequently be called into question. The case before the Pennsylvania Supreme Court raises a different issue—once the basic proof satisfies Frye, does the trial judge still have a gate-keeping role?

The case—Walsh v. BASF, 14-18 WAP 2019, was argued on Oct. 19. At the trial of this wrongful death and products liability case, the trial judge excluded expert testimony. The Superior Court reversed, holding that the trial judge delved too deeply into the expert evidence: the Frye inquiry herein was overly expansive. The court viewed its role as that of a gatekeeper, charged with "reviewing the studies that Dr. Nachman Brautbar relies upon to determine whether they support Brautbar's reliance," and "to make sure that the articles stood for what Brautbar said that they did." That is not the proper role of the trial court in a Frye inquiry.

The Superior Court elaborated on what it found to be excessive gatekeeping: "The court scrutinized the studies cited by Brautbar, assessed their scientific relevance and validity, and then arrived at its own conclusion whether the expert's reliance upon them was scientifically acceptable. The court's finding that Brautbar did not follow accepted methodologies in relying upon certain studies in forming his opinions as to general causation added another layer to the generally accepted methodology requirement."

In granting allowance of appeal, the Supreme Court agreed to consider two questions:

• Did the Superior Court majority commit reversible error in concluding that, when evaluating scientific evidence under the Frye standard, trial courts are not permitted to act as "gatekeepers" to ensure the relevance and reliability of scientific studies offered by experts to support their opinions by scrutinizing whether those studies actually support their opinions?
• Did the Superior Court majority commit reversible error in concluding that trial courts may not review experts' opinions extrapolating from a broad class of products and injuries to a specific product and injury, thereby eliminating the plaintiff's burden to show product-specific causation of the plaintiff's specific injury?

It is impossible to predict how the court will rule. But given its remand order in Ross, it is clear that in Pennsylvania Frye determinations do not last forever, and are subject to reassessment as science grows. And given the gradual move to permit a Frye inquiry into how a methodology was applied, there is at least a gatekeeping role for Pennsylvania judges.

Jules Epstein is professor of law and director of advocacy programs at Temple University Beasley School of Law.