The Pennsylvania Superior Court recently issued an opinion in Walsh v. BASF Corp. addressing the gatekeeper role of the trial judge when reviewing and ruling on the admissibility of expert causation opinions. The PA Superior Court vacated orders entered by the trial court precluding the plaintiff’s medical causation experts from testifying as to whether Acute Myelogenous Leukemia (“AML”) was caused by exposure to various pesticides.  The PA Superior Court felt that the experts could offer a causation opinion without the support of an existing study establishing a link between AML and exposure to the chemicals at issue; and that the trial judge exceeded his role as the gatekeeper by reviewing studies cited by the experts to determine if they actually stand for the cited propositions. This decision, if it stands, may reduce the level of Frye scrutiny employed by PA trial court judges and may permit more novel causation opinions to be presented to juries.

In Walsh, it is alleged that a groundskeeper and golf course superintendent developed AML as a result of exposure to various pesticides that he handled and applied over the course of almost 40 years. The defendant pesticide manufacturers filed a motion to exclude the plaintiff’s causation experts pursuant to Frye v. United States and corresponding summary judgment motions. The defendants argued that the plaintiff’s claims should be dismissed because the plaintiff’s experts did not follow the Bradford Hill criteria in reaching their causation opinions as there are no studies establishing a link between AML and exposure to the chemicals found in the various pesticides at issue. The trial judge granted the motions finding that the opinions of the plaintiff’s experts were not supported by generally accepted scientific methodology. The trial judge reviewed multiple studies cited by the plaintiff’s experts and pointed out how he felt that many of the studies did not support the propositions proffered by the plaintiff’s experts. Plaintiff’s counsel argued that the trial judge inappropriately evaluated the correctness of the experts’ conclusions rather than examining the general acceptability of the methodologies used to formulate those opinions. The trial judge wrote in a memorandum opinion that he believes contrary to the plaintiff’s position that it is the court’s role to evaluate whether an expert’s cited authorities stand for what they are cited for. “Under Plaintiff’s approach, [the expert] may cite a study regarding traffic patterns in New York City for the proposition that chemical a causes AML in humans.” Otherwise, the court would not be serving as a proper gatekeeper.

The PA Superior Court disagreed with the trial judge and vacated the orders precluding the plaintiff’s causation experts and granting the defendants’ motions for summary judgment. The three-judge panel did not believe that the proper role of the trial court in a Frye inquiry is to review studies and other scientific literature and reach a conclusion on their proper meaning and interpretation. The court felt that when a trial judge applies his own view of which studies are scientifically or medically acceptable to support an expert’s opinion, the trial court impermissibly is setting itself up as a “super expert in the field of medicine.” While the court acknowledged that the epidemiological studies cited by the plaintiff’s experts “did not explore whether exposure to one particular pesticide product caused AML” it rejected the contention that specific studies of this type are required in order to survive a Frye challenge. “For purposes of Frye, an expert need not rely on studies that mirror the exact facts under consideration. It is sufficient if the synthesis of various legitimate studies reasonably permits the conclusion reached by the expert. The absence of a treatise or study directly on point goes to the weight, not the admissibility, of expert opinion. An expert’s opinion will satisfy Frye when it is deduced from generally accepted scientific principles and supported by studies or literature, even where the expert could not point to one study involving parallel circumstances.”

It is unknown at this time whether the defendants in Walsh will appeal the Super Court’s decision to the Pennsylvania Supreme Court.

The Walsh decision, if it stands, may dissuade PA trial court judges from carefully scrutinizing the underlying basis for an expert’s opinion and may result in more novel expert opinions to be presented to a jury. Per Walsh an expert is not required to point to existing literature or study that is directly on point and supports the proffered causation opinion. Rather, all that may be necessary is that the expert be able to point to some combination of articles and studies that reasonably permits the expert to reach his or her conclusions. It will then be up to a jury of lay people to make the determination as to whether such a conclusion or causation opinion is reasonable and sound.