Leave it to the Experts: A Review of Recent Pennsylvania Decisions & Standards Regarding Expert Testimony

In three recent decisions, Pennsylvania courts examined the role of the court during Frye proceedings, the opponent’s burden of proof when challenging expert testimony, and the proper foundation necessary for utilizing a learned treatise to cross-examine/impeach a witness. The following summarizes these opinions and provides pragmatic reminders of evidentiary rules and standards for Pennsylvania trial attorneys.

Adherence to Frye: The Limited Role of the Trial Judge
In Walsh v. BASF Corp., 234 A.3d 446 (Pa. 2020), the Supreme Court affirmed the Superior Court’s decision which found that the trial court went beyond the scope of its permitted role during a Frye hearing when it made “itself the arbiter of what research could be scientifically relied upon to support an expert’s opinion.”

Experts for the appellants opined that testimony of the experts proffered by the appellee “failed to apply methodologies generally accepted in the relevant scientific communities.” Although the trial court did not abuse its discretion in conducting a Frye inquiry based on appellants’ challenge to appellee’s expert testimony, the Supreme Court stressed that “the trial court may consider only whether the expert applied methodologies generally accepted in the relevant field, and may not go further to attempt to determine whether it agrees with the expert’s application of those methodologies or whether the expert’s conclusions have sufficient factual support” as those are “questions for the jury to decide.” Even in making this determination, the trial court must be “guided by scientists in the relevant field” and “not upon any scientific expertise of judges.”

The Supreme Court explained that while the Frye test requires that the expert’s methodology be generally accepted, “the conclusions reached from those applications need not also be generally accepted.” Thus, during its inquiry, the trial court must not question the “merits of the expert’s scientific theories, techniques or conclusions” nor “assess whether it considers those theories, techniques and/or conclusions to be accurate or reliable” as that is exactly what the Frye test seeks to avoid.

Initial Burden of Proof is on the Challenger Opposing Expert Testimony
In Cmmw. v. Bonnett, 239 A.3d 1096 (Pa. Super. 2020), the defense failed to satisfy their burden of proof when challenging the testimony of the prosecution’s fire causation expert. Without proffering its own expert to challenge the testimony of the prosecution’s expert, the defense asserted that the expert’s testimony did not comport with the “National Fire Protection Association Publication 921 (‘NFPA 921’), the scientific methodology deemed acceptable in the fire investigation community” and moved the trial court for a Frye hearing on the issue. Following argument by the parties, the trial court refused to conduct a Frye hearing and the defense appealed.

Affirming the trial court’s decision, the Superior Court held that the defense failed to “make an initial showing” that the testimony of the prosecution’s expert was “based on novel scientific evidence.” The court explained that “a party opposing … scientific evidence must demonstrate that the expert’s testimony is based on novel scientific evidence.” Importantly, scientific evidence is “novel when there is a legitimate dispute regarding the reliability of the expert’s conclusions.” Once the moving party has identified novel scientific evidence, the burden then shifts to the proponent of such evidence to show that the “expert’s methodology has general acceptance in the relevant scientific community despite the legitimate dispute.”

The defense erroneously believed that they had no burden to show that the fire causation expert’s methods were novel, arguing that the issue was not whether the expert “used a novel scientific method” but rather whether the expert “applied the accepted scientific methodology set forth in [NFPA] 921 in a conventional fashion in reaching her conclusions.”

The Superior Court noted that in requesting the Frye hearing on the expert’s conclusions, the defense was essentially asking the “court to usurp the jury’s role to question the merits of [the expert’s] techniques and conclusions” – which, as previewed in Walsh, fell outside the permitted role of the court.

Utilizing a Learned Treatise to Cross-Examine/Impeach a Witness
In Charlton v. Troy, 236 A.3d 22 (Pa. Super. 2020), the Superior Court vacated a jury verdict and remanded the medical malpractice case for a new trial, after it found that the lower court erred when it allowed plaintiff’s counsel to cross-examine the defendant physician about the contents of a medical textbook that the witness did not recognize as authoritative or reliable. The Superior Court found that use of the medical textbook was extremely prejudicial to the defense.

Noting that the Pennsylvania Rules of Evidence do not recognize a hearsay exception for a learned treatise, the Superior Court found that no foundation was laid to establish the medical textbook as a learned treatise (i.e. “any textbook, published work, or periodical that has been accepted as authoritative or as reliable … by members of a specific professional community”) for the limited purpose of impeaching the defendant physician. The court explained that while such materials are inadmissible, “an expert may be impeached with statements contained in a text or publication deemed authoritative or reliable by [the witness] or other experts in the same field.” In other words, in order to “cross-examine an expert with a treatise, either that expert or another expert in the field must attest to the publication’s reliability.” Absent such foundation, the text cannot be used for cross-examination.

The court found that the defendant physician did not testify as an expert witness. Notwithstanding, the court stated that, as a fact witness, the defendant physician could be “cross-examined with a publication that he agreed was authoritative or reliable.” However, no such foundation was laid since the defendant physician did not recognize the subject textbook as authoritative. Thus, the court held that whether the defendant physician is “viewed as an expert or a fact witness, the trial court erred in permitting him to be cross-examined with a text that neither he nor any expert witness had established as authoritative or reliable” in the subject field.