      [J-92A-2019, J-92B-2019, J-92C-2019, J-92D-2019 and J-92E-2019]
               IN THE SUPREME COURT OF PENNSYLVANIA
                           WESTERN DISTRICT

 SAYLOR, C.J., BAER, TODD, DONOHUE, DOUGHERTY, WECHT, MUNDY, JJ.


RICHARD THOMAS WALSH,                  :   No. 14 WAP 2019
EXECUTOR OF THE ESTATE OF              :
THOMAS J. WALSH, DECEASED              :   Appeal from the Order of the Superior
                                       :   Court entered June 20, 2018 at No.
                                       :   1661 WDA 2016 vacating the Order of
           v.                          :   the Court of Common Pleas of
                                       :   Allegheny County entered October
                                       :   14, 2016 at No. GD 10-018588, and
BASF CORPORATION; BAYER                :   remanding
CORPORATION D/B/A BAYER                :
CROPSCIENCE, L.P., AND BAYER           :   ARGUED: October 16, 2019
CROPSCIENCE HOLDING, INC.,             :
AND/OR BAYER CROPSCIENCE, L.P.         :
AND BAYER CROPSCIENCE HOLDING,         :
INC., IN THEIR OWN RIGHT; BIOSAFE      :
SYSTEMS, L.L.C.; CHEMTURA              :
CORPORATION; CLEARY CHEMICAL           :
CORP.; DOW AGROSCIENCES, L.L.C.;       :
E.H. GRIFFITH, INC.; E.I. DU PONT DE   :
NEMOURS AND CO., INC.; G.B.            :
BIOSCIENCES CORPORATION; JOHN          :
DEERE LANDSCAPING, INC.,               :
SUCCESSOR TO LESCO, INC.;              :
MONSANTO COMPANY; NUFARM               :
AMERICAS, INC.; REGAL CHEMICAL         :
CO.; SCOTTS-SIERRA CROP                :
PROTECTION CO.; AND SYNGENTA           :
CROP PROTECTION, INC.                  :
                                       :
                                       :
APPEAL OF: DOW AGROSCIENCES,           :
LLC, BAYER CROPSCIENCE, LP,            :
BAYER CORPORATION, AND BAYER           :
CROPSCIENCE HOLDING, INC.              :

RICHARD THOMAS WALSH,                  : No. 15 WAP 2019
EXECUTOR OF THE ESTATE OF              :
THOMAS J. WALSH, DECEASED              : Appeal from the Order of the Superior
                                       : Court entered June 20, 2018 at No.
                                         :   1661 WDA 2016, vacating the Order
            v.                           :   of the Court of Common Pleas of
                                         :   Allegheny County entered October
                                         :   14, 2016 at No. GD 10-018588, and
BASF CORPORATION; BAYER                  :   remanding
CORPORATION D/B/A BAYER                  :
CROPSCIENCE, L.P., AND BAYER             :   ARGUED: October 16, 2019
CROPSCIENCE HOLDING, INC.,               :
AND/OR BAYER CROPSCIENCE, L.P.           :
AND BAYER CROPSCIENCE HOLDING,           :
INC., IN THEIR OWN RIGHT; BIOSAFE        :
SYSTEMS, L.L.C.; CHEMTURA                :
CORPORATION; CLEARY CHEMICAL             :
CORP.; DOW AGROSCIENCES, L.L.C.;         :
E.H. GRIFFITH, INC.; E.I. DU PONT DE     :
NEMOURS AND CO., INC.; G.B.              :
BIOSCIENCES CORPORATION; JOHN            :
DEERE LANDSCAPING, INC.,                 :
SUCCESSOR TO LESCO, INC.;                :
MONSANTO COMPANY; NUFARM                 :
AMERICAS, INC.; REGAL CHEMICAL           :
CO.; SCOTTS-SIERRA CROP                  :
PROTECTION CO.; AND SYNGENTA             :
CROP PROTECTION, INC.                    :
                                         :
                                         :
APPEAL OF: DEERE & COMPANY               :

RICHARD THOMAS WALSH,                    :   No. 16 WAP 2019
EXECUTOR OF THE ESTATE OF                :
THOMAS J. WALSH, DECEASED                :   Appeal from the Order of the Superior
                                         :   Court entered June 20, 2018 at No.
                                         :   1661 WDA 2016, vacating the Order
            v.                           :   of the Court of Common Pleas of
                                         :   Allegheny County entered October
                                         :   14, 2016 at No. GD 10-018588, and
BASF CORPORATION; BAYER                  :   remanding
CORPORATION D/B/A BAYER                  :
CROPSCIENCE, L.P., AND BAYER             :   ARGUED: October 16, 2019
CROPSCIENCE HOLDING, INC.,               :
AND/OR BAYER CROPSCIENCE, L.P.           :
AND BAYER CROPSCIENCE HOLDING,           :
INC., IN THEIR OWN RIGHT; BIOSAFE        :
SYSTEMS, L.L.C.; CHEMTURA                :
CORPORATION; CLEARY CHEMICAL             :
CORP.; DOW AGROSCIENCES, L.L.C.;         :



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E.H. GRIFFITH, INC.; E.I. DU PONT DE     :
NEMOURS AND CO., INC.; G.B.              :
BIOSCIENCES CORPORATION; JOHN            :
DEERE LANDSCAPING, INC.,                 :
SUCCESSOR TO LESCO, INC.;                :
MONSANTO COMPANY; NUFARM                 :
AMERICAS, INC.; REGAL CHEMICAL           :
CO.; SCOTTS-SIERRA CROP                  :
PROTECTION CO.; AND SYNGENTA             :
CROP PROTECTION, INC.                    :
                                         :
                                         :
APPEAL OF: SYNGENTA CROP                 :
PROTECTION, INC.                         :

RICHARD THOMAS WALSH,                    :   No. 17 WAP 2019
EXECUTOR OF THE ESTATE OF                :
THOMAS J. WALSH, DECEASED                :   Appeal from the Order of the Superior
                                         :   Court entered June 20, 2018 at No.
                                         :   1661 WDA 2016, vacating the Order
            v.                           :   of the Court of Common Pleas of
                                         :   Allegheny County entered October
                                         :   14, 2016 at No. GD 10-018588, and
BASF CORPORATION; BAYER                  :   remanding
CORPORATION D/B/A BAYER                  :
CROPSCIENCE, L.P., AND BAYER             :   ARGUED: October 16, 2019
CROPSCIENCE HOLDING, INC.,               :
AND/OR BAYER CROPSCIENCE, L.P.           :
AND BAYER CROPSCIENCE HOLDING,           :
INC., IN THEIR OWN RIGHT; BIOSAFE        :
SYSTEMS, L.L.C.; CHEMTURA                :
CORPORATION; CLEARY CHEMICAL             :
CORP.; DOW AGROSCIENCES, L.L.C.;         :
E.H. GRIFFITH, INC.; E.I. DU PONT DE     :
NEMOURS AND CO., INC.; G.B.              :
BIOSCIENCES CORPORATION; JOHN            :
DEERE LANDSCAPING, INC.,                 :
SUCCESSOR TO LESCO, INC.;                :
MONSANTO COMPANY; NUFARM                 :
AMERICAS, INC.; REGAL CHEMICAL           :
CO.; SCOTTS-SIERRA CROP                  :
PROTECTION CO.; AND SYNGENTA             :
CROP PROTECTION, INC.                    :
                                         :
                                         :
APPEAL OF: MONSANTO COMPANY              :



      [J-92A-2019, J-92B-2019, J-92C-2019, J-92D-2019 and J-92E-2019] - 3
 RICHARD THOMAS WALSH,                       :    No. 18 WAP 2019
 EXECUTOR OF THE ESTATE OF                   :
 THOMAS J. WALSH, DECEASED                   :    Appeal from the Order of the Superior
                                             :    Court entered June 20, 2018 at No.
                                             :    1661 WDA 2016, vacating the Order
              v.                             :    of the Court of Common Pleas of
                                             :    Allegheny County entered October
                                             :    14, 2016 at No. GD 10-018588, and
 BASF CORPORATION; BAYER                     :    remanding
 CORPORATION D/B/A BAYER                     :
 CROPSCIENCE, L.P., AND BAYER                :    ARGUED: October 16, 2019
 CROPSCIENCE HOLDING, INC.,                  :
 AND/OR BAYER CROPSCIENCE, L.P.              :
 AND BAYER CROPSCIENCE HOLDING,              :
 INC., IN THEIR OWN RIGHT; BIOSAFE           :
 SYSTEMS, L.L.C.; CHEMTURA                   :
 CORPORATION; CLEARY CHEMICAL                :
 CORP.; DOW AGROSCIENCES, L.L.C.;            :
 E.H. GRIFFITH, INC.; E.I. DU PONT DE        :
 NEMOURS AND CO., INC.; G.B.                 :
 BIOSCIENCES CORPORATION; JOHN               :
 DEERE LANDSCAPING, INC.,                    :
 SUCCESSOR TO LESCO, INC.;                   :
 MONSANTO COMPANY; NUFARM                    :
 AMERICAS, INC.; REGAL CHEMICAL              :
 CO.; SCOTTS-SIERRA CROP                     :
 PROTECTION CO.; AND SYNGENTA                :
 CROP PROTECTION, INC.                       :
                                             :
                                             :
 APPEAL OF: BASF CORPORATION                 :


                                       OPINION


JUSTICE DONOHUE                                  DECIDED: JULY 21, 2020

      Appellants, the manufacturers of various pesticides, appeal from the decision of

the Superior Court reversing the trial court’s grant of summary judgment in their favor

following the trial court’s determination that the testimony of the experts proffered by

Appellee, the Executor of the Estate of Thomas J. Walsh (“Walsh”), failed to satisfy the


        [J-92A-2019, J-92B-2019, J-92C-2019, J-92D-2019 and J-92E-2019] - 4
test set forth in Frye v. United States, 293 F. 1013 (D.C. Cir. 1923). For the reasons set

forth herein, we affirm the Superior Court’s ruling, with instructions that on remand to the

trial court, the Appellants should be given the opportunity to renew their Frye motions for

the reasons addressed in this Opinion.

                         Factual and Procedural Background

       For nearly forty years, Walsh served as a groundskeeper and golf course

superintendent at several Pittsburgh area golf courses. His work involved the regular

application of various pesticides (primarily insecticides and fungicides) on the golf

courses. Over this time, Walsh kept a detailed record of his activities regarding the

pesticides he used, including a detailed log of the specific products and the dates of their

applications. In addition, a coworker, Blaise Santoriello, testified with regard to Walsh’s

activities, including how the pesticides were applied, the protective gear they wore when

doing so, what pesticides were used and in what concentrations. In the early years,

gloves were the only protective gear that they used, although in later years they also wore

overalls, rubber boots and masks. Eventually they began wearing disposable protective

gear. Even with these protections, Santoriello explained, exposure to the dust from the

pesticide products would occur while opening the bags and mixing the chemicals.

       On October 5, 2008, Walsh was suffering from fever, chills, and a cough when he

arrived at an emergency room. A bone marrow biopsy resulted in a diagnosis of Acute

Myelogenous Leukemia (“AML”). Cytogenetic testing revealed significant chromosomal

aberrations. On February 2, 2009, Walsh died. His treating oncologist, James Rossetti,

D.O., later opined that Walsh’s extensive exposure to pesticides raised a high degree of

suspicion that said exposure played a significant role in the development of his AML.




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      Walsh’s executor commenced this wrongful death and survival action against the

manufacturers of various pesticides that he had applied during his career, asserting

claims in strict products liability, negligence, and breach of warranty. Based upon a lack

of expert testimony identifying various pesticides as substantial contributing factors in

Walsh’s death, the trial court granted summary judgment in favor of a large number of

manufacturers. Appellants, the remaining manufacturers, manufacture fifteen pesticides

products to which Walsh was exposed.

      Three of the current Appellants, Bayer CropScience LP, Bayer Corporation and

Bayer CropScience Holdings, Inc. (collectively “Bayer”), filed a Frye motion1 to exclude

the testimony of the Executor’s expert witnesses, Nachman Brautbar, M.D (“Dr.

Brautbar”) and April Zambelli-Weiner, Ph.D. (“Dr. Zambelli-Weiner”). The remaining

defendants either joined Bayer’s Frye motion or filed their own. In these motions, the

Appellants alleged that Drs. Brautbar and Zambelli-Weiner failed to apply methodologies

generally accepted in the relevant scientific communities.

      In his original expert report,2 Dr. Brautbar explained that “[k]nowledgeable

physicians approach the question whether a person’s disease was caused by a particular

chemical by considering two separate, but related, questions.” Brautbar Initial Report,

2/17/2014, at 13. The first question is whether the chemical can cause “the particular



1 See Pa.R.C.P. 207.1 (“Motion to Exclude Expert Testimony Which Relies upon Novel
Scientific Evidence”).
2 In his original expert report, Dr. Brautbar discussed the methodologies he employed
and gave an overview of what the nine Bradford Hill factors entailed (discussed infra). In
a supplemental expert report, Dr. Brautbar provided a thorough analysis of his
observations and conclusions with respect to each factor. Brautbar Supplemental Report,
10/22/2015, at 3-13.


        [J-92A-2019, J-92B-2019, J-92C-2019, J-92D-2019 and J-92E-2019] - 6
condition the person has” (general causation), and the second question is “whether a

chemical that is capable of causing the condition that the person has actually caused the

person’s condition.” Id. For general causation, Dr. Brautbar described the generally

accepted methodology he employed as follows:

                (1) identify all relevant studies, (2) read and critically evaluate
                all the relevant studies, (3) evaluate all the data based upon
                recognized scientific factors (the Bradford Hill viewpoints) and
                other factors relevant to the chemical and the disease; (4)
                exercise best professional judgment in reaching a conclusion
                on the issue of whether a particular chemical or class of
                chemicals can cause a particular disease; and (5) explain the
                factual basis and the reasoning supporting the conclusion.

Id.

       With respect to causality, Dr. Brautbar indicated that he utilized the “Bradford Hill

criteria” or “viewpoints,” a set of nine factors used to determine whether a recognized

association is in fact a causal link. Id. at 13-15 (citing Sir Austin Bradford Hill, The

Environment and Disease: Association or Causation, Section of Occupational Medicine,

at 295 (January 1965)). In his 1965 article,3 Sir Bradford Hill indicated that his new

methodology was necessary to decide whether an observed association between a

potential toxin and a particular disease was in fact the outcome of an actual causal

relationship.

                [M]ore often than not we are dependent upon our observation
                and enumeration of defined events for which we then seek
                antecedents. In other words, we see that the event B is
                associated with the environmental feature A, that, to take a
                specific example, some form of respiratory illness is
                associated with a dust in the environment.          In what
                circumstances can we pass from this observed association


3  Sir Bradford Hill’s focus at the time was to determine whether there was a causal
relationship between smoking and lung cancer.


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                to a verdict of causality? Upon what basis should we proceed
                to do so?

Id. (emphasis in original).

       After an association between agent and disease has been identified, the nine

factors are evaluated to determine the strength of that association, with a strong

association pointing to a causal relationship. Sir Bradford Hill explained the process as

follows:

                Here then are nine different viewpoints from all of which we
                should study association before we cry causation. What I do
                not believe – and this has been suggested is that that we can
                usefully lay down some hard-and-fast rules of evidence that
                must be obeyed before we accept cause and effect. None of
                my nine viewpoints can bring indisputable evidence for and
                against the cause-and-effect hypothesis and none can be
                required as a sine qua non. What they can do, with greater or
                less strength, is help us to make up our minds on the
                fundamental question – is there any other way of explaining
                the set of facts before us, is there any other answer equally,
                or more, likely than cause and effect.

Id. at 299.

       The nine criteria are (1) consistency of the observed association, (2) strength of

the observed association, (3) specificity of the observed association, (4) temporal

relationship of the observed association, (5) biological gradient, (6) biological plausibility,

(7) coherence, (8) experimental evidence from human populations, and (9) analogy. Id.

at 295-99. According to Dr. Brautbar, these criteria are widely accepted in the relevant

scientific community, including by scientific bodies (e.g., the World Health Organization)

and in modern textbooks on epidemiology, occupational and environmental medicine, and

toxicology. Brautbar Initial Report, 2/17/2014, at 15-16. Dr. Brautbar stresses that there

is no formula or algorithm for assessing the factors, but rather it requires judgment and




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scientific expertise to measure the weight and significance of each factor when

conducting a particular evaluation. Id. at 16-17.

       In his original expert report, Dr. Brautbar provided an overview of what the nine

Bradford Hill factors entailed, and then a supplemental expert report filed after the reports

of the Appellants’ experts had been received. In the supplemental report, Dr. Brautbar

provided a detailed analysis of his observations and conclusions with respect to each

factor, including “the facts and studies that I rely on [to] provide evidence supportive of

causality under each of the Bradford Hill factors… .” Brautbar Supplemental Report,

10/22/2015, at 2. In this supplemental report, he observed that all of the experts in the

case agreed that the Bradford Hill factors was the appropriate methodology to assess

causation in this case. Id. He explained that the differing conclusions of the Appellants’

experts “is due to differences in professional judgment, rather than methodology,”

indicating that “different experts may reach differing conclusions based upon their best

exercise of professional judgment, even though they may employ the same generally

accepted methodology, they may rely on generally the same body of literature, and may

base their opinion on the same facts relative to the patient and the workplace.” Id.

       Dr. Brautbar conducted his Bradford Hill factors analysis on the association

between AML and pesticides. While conducting his analysis, he did not mention the

pesticides manufactured by any of the Appellants or refer to any articles or studies relating

to any specific pesticide or product. Having concluded that the Bradford Hill factors

supported the existence of a causal link between AML and pesticides generally, he then

acknowledged that because “some pesticides cause [AML] does not necessarily mean

that all pesticides cause this disease.” Id. He proceeded to conduct product-specific




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analyses of each product manufactured by the Appellants, including detailed tables

attached to his report identifying every exposure that Walsh had to each product

(including by date and specific product) (hereinafter “Exhibit B”4) as well as the

carcinogenic potential for the active ingredients in each product (hereinafter “Exhibit C”5).

He did not purport to present direct evidence of a causal link between AML and the

Appellants’ specific products. Instead Dr. Brautbar opined that the causal link could be

demonstrated indirectly. In particular, he identified studies that demonstrated that the

active ingredients in these specific pesticides are genotoxic and thus cause chromosomal

abnormalities. In what he refers to as the “fingerprint theory,” he cited to studies showing

that when exposure to pesticides or benzene causes AML, cytogenetic review identifies

a unique set of chromosomal abnormalities (abnormalities of the fifth and seventh

chromosomes), which in turn start the process to carcinogenicity. Brautbar Initial Report,

2/17/2014, at 22.    According to Dr. Brautbar, this specific pattern of chromosomal

abnormalities were identified in the cytogenetic testing performed on Walsh.

       For specific causation, Dr. Brautbar utilized a differential diagnosis (or differential

etiology) methodology, which he explained involves “ruling in all identifiable known

causes of (and risk factors for) [the disease in question] and then ruling out those for

which there is inadequate evidence.” Id. at 61. According to Dr. Brautbar, “[t]he remaining




4  Exhibit B sets forth, in column form, the company and pesticide, toxicity per MSDS,
Thomas Walsh exposure history per Complaint, pages of deposition, and a summary of
testimony of co-worker (Santoriello).
5  Exhibit C sets forth, in column form, the company, product, composition, EPA cancer
classification, human cancer, animal carcinogen, and cytogenicity, cytotoxicity,
genotoxicity and immunotoxicity.


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cause(s) would then be deemed the probable cause(s) provided that substantial scientific

and medical evidence exists for causality.” Id.

       Dr. Zambelli-Weiner conducted what she described as a critical review of “the

published epidemiological literature on pesticide exposure and leukemia.” Zambelli-

Weiner Report, 7/18/2012, at 4. She indicated that in assessing the causal assessment,

she employed a variety of methodologies, “including reviews, meth-analysis, weight-of-

the-evidence analyses and application of the Bradford Hill criteria for causality.” Id. at 5.

She concluded that “exposure to organophosphate pesticide formulations, individually or

in combination, is causally related to an increased risk of leukemia in humans exposed to

them.” Id. at 15.

       The trial court did not conduct a Frye hearing, but rather ordered the parties to

conduct depositions and file briefs.     Upon review of these materials and after oral

arguments by counsel, the trial court granted the Appellants’ Frye motions by written

opinion. It first concluded that Dr. Brautbar’s expert report did not establish either general

or specific causation for pesticides not containing benzene.           Trial Court Opinion,

10/5/2016, at 2-13.     With respect to pesticides containing benzene, the trial court

determined that Dr. Brautbar’s expert report demonstrated general causation, as it cited

to numerous studies showing that exposure to benzene “at some level” may cause AML.

Id. at 13-19. The trial court rejected Dr. Brautbar’s specific causation analysis with regard

to benzene products, however, because it concluded that the reports and studies he cited

did not support the contention that low level exposures of benzene could cause AML. Id.

at 13-17. The trial court also refused to credit Dr. Brautbar’s alternative theory of specific




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causation, namely the ‘fingerprint theory” that Dr. Brautbar claimed resulted in no cases

of idiopathic instances of AML (no known external cause). Id. at 18-19.

      Because Dr. Brautbar’s expert report did not establish specific causation for any

of the Appellants’ products, the trial court decided that it was not necessary to consider

Dr. Zambelli-Weiner’s expert report (which was offered only for general causation

purposes). Id. at 19. The trial court noted that it did not consider Dr. Zambelli-Weiner’s

“pesticides as a class” opinion to be in accordance with generally accepted scientific

methodology “because it fails to account for variations in composition of the universe of

chemicals, compounds, or the like that might be considered a pesticide.” Id. The trial

court did not cite to any authority or expert testimony of record in support of this

conclusion.

      In light of the trial court’s grant of the Appellants’ Frye motions, the parties

stipulated to the entry of summary judgment “in favor of all remaining defendants and

against [Walsh] on all of [Walsh’s] remaining claims, … with all rights of appeal

preserved.” Stipulated Order of Court, 19/14/2016.

      The Executor then appealed to the Superior Court and the trial court issued a

Pa.R.A.P. 1925(a) opinion. The Superior Court reversed the trial court’s grant of the

Appellants’ Frye motions. Walsh v. BASF Corp., 191 A.3d 838 (Pa. Super. 2018), appeal

granted, 203 A.3d 976 (Pa. 2019). It began by denying the Executor’s contention that the

causal relationship “has crossed the threshold from novel science to general acceptance.”

Id. at 844. Despite acknowledging that there are more than 700 scholarly articles and

studies examining this causal relationship, the Superior Court recognized that in Betz v.

Pneumo Abex LLC, 44 A.3d 27 (Pa. 2012), this Court indicated that “a reasonably broad




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meaning should be ascribed to the term ‘novel,’” and that application of the Frye standard

is necessary when a trial court has “articulable grounds to believe that an expert has not

applied generally accepted scientific methodology in a conventional fashion in reaching

his conclusions.” Id. (citing Betz, 44 A.3d at 47). Because some of Appellants’ experts

had opined that the Executor’s experts had not applied generally accepted methodologies

in a conventional way, the Superior Court concluded that the trial court did not abuse its

discretion in conducting a Frye inquiry. Id.

       However, the Superior Court held that the trial court, by making itself the arbiter of

what research could be scientifically relied upon to support an expert’s opinion, had

overstepped its “gatekeeper” function because that is “not the proper role of the trial court

in a Frye inquiry.” Id. at 844. The Superior Court cited to this Court’s decision in

Commonwealth v. Topa, 369 A.2d 1277 (Pa. 1977), in which we indicated that we adopted

the Frye test to avoid having judges try to understand the complexities of modern science,

as it is better to allow the scientists to do that to ensure reliability. Id. at 842-43 (citing

Topa, 369 A.2d at 1282).

       The Superior Court further rejected the trial court’s determination that the research

relied upon by Dr. Brautbar was not scientifically acceptable because, on some

occasions, the conclusion of the study’s author were contrary to those of Dr. Brautbar.

Id. at 843. The court cited to a dissent by then-Chief Justice Castille in Blum v. Merrell

Dow Pharma., Inc., 764 A.2d 1 (Pa. 2000), in which he noted that limiting an expert

testifying to the conclusions of other scientists would conclusively set in stone the views

of the first researcher. Walsh, 191 A.3d at 846 (citing Blum, 764 A.2d at 15 (Castille, J.,




        [J-92A-2019, J-92B-2019, J-92C-2019, J-92D-2019 and J-92E-2019] - 13
dissenting)). Instead, any conclusion reached by application of generally acceptable

methodologies meets the Frye test.

       The Appellants argued that generally accepted methodologies do not permit a

scientist to extrapolate from studies involving harm from a broad product class

(pesticides) to a specific product (Appellant’s chemicals) causing a specific harm (AML).

In other words, the Appellants indicated that Dr. Brautbar needed to rely on studies

identifying a causal link between their specific product and AML. The Appellants likewise

insisted that it was inappropriate for Dr. Brautbar to rely upon animal studies or in vitro

(test tube) experiments instead of epidemiology studies involving humans.

       As to the first point, the Superior Court held that an expert need not rely on studies

that mirror the exact facts under consideration. Id. at 848. It is sufficient if the synthesis

of various legitimate studies reasonably permits the conclusion reached by the expert.

Id. The absence of a treatise or study directly on point goes to the weight, not the

admissibility, of expert opinion. Id. An expert’s opinion will satisfy Frye when it is deduced

from generally acceptable scientific principles and supported by studies or literature, even

where the expert could not point to one study involving precisely parallel circumstances.

Id. The Superior Court disagreed that studies of Appellant’s particular products were

required, as the EPA regularly conducts studies on the cumulative risk of broad classes

of pesticides that share similar “mechanisms of toxicity or act the same way in the body.”

Id. at 847. Many of the articles/studies by the Executor’s experts looked at multiple

pesticide exposures in agricultural settings, based upon the notion that this approach

presents a better picture of occupational exposure to various pesticides (which are

typically used in combination rather than singularly). Id. Zambelli-Weiner’s expert report




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indicated that most epidemiological studies are conducted on exposures to classes of

pesticides because they are “additive, cumulative, and synergetic.” Id.

      As to the second point, the Superior Court noted that scientists routinely conduct

and rely upon animal studies and/or in vitro testing. Id. at 847. Dr. Brautbar did not rely

exclusively on such studies. Id. Dr. Brautbar also relied upon human studies of pesticide

exposure by golf course superintendents (like Walsh), farmers, and other pesticide

applicators subject to occupational pesticides. Id. According to the court, all of these

studies, in the aggregate, support a causal link between pesticide exposure and leukemia

(including AML).

      Finally, the Superior Court responded to the trial court’s rejection of Dr. Brautbar’s

opinion that medical science, in the form of cytogenetic studies of chromosomal

aberrations, was proof of a causal link resulting in AML. The trial court indicated that

these studies were not conclusive but the Superior Court disagreed, indicating that “we

find the existence of these studies, together with the differential etiology methodology

employed by Dr. Brautbar, sufficient to pass muster under Frye. Id. at 848.

      In dissent, Judge Bender held that that the trial court’s review of the studies relied

upon by Plaintiff's experts was “necessary to prevent experts from `evad[ing] a reasoned

Frye inquiry by making reference to accepted methods in the abstract.’” Id. at 849

(Bender, J., dissenting). According to Judge Bender, “more particularity is necessary"

than the pesticide class methodology deemed sufficient by the majority. Id. at 850.

      On appeal, the Appellants raise three issues:

I.    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




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       of scientific studies offered by experts to support their opinions by
       scrutinizing whether those studies actually support their opinions?

II.    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 plaintiff’s burden to show product-specific causation of plaintiff's
       specific injury?

III.   Did the Superior Court majority commit reversible error in concluding that
       the trial court erred without explaining how it abused its discretion because
       of manifest unreasonableness, partiality, prejudice, bias, ill-will or such lack
       of support from the evidence or the record so as to be clearly erroneous?

Walsh v. BASF Corp., 203 A.3d 976 (Pa. 2019). Although technically the trial court

granted summary judgment by consent of the parties, its ruling was based upon its

interlocutory decision on the Appellants’ Frye motions.           The appropriate appellate

standard of review is typically the one pertaining to the underlying ruling. See Gallagher

v. PLCB, 883 A.2d 550, 559 n.11 (Pa. 2005). When reviewing a trial court’s grant or

denial of a Frye motion, an abuse of discretion standard applies. Betz, 44 A.3d at 54.

Accordingly, we will apply an abuse of discretion standard in our review of the trial court’s

grant of the Appellants’ Frye motions.

       We begin our discussion with Rule 702 of the Pennsylvania Rules of Evidence.

Rule 702, entitled “Testimony by experts,” which controls the admissibility of expert

testimony on scientific knowledge, states:

              A witness who is qualified as an expert by knowledge, skill,
              experience, training, or education may testify in the form of an
              opinion or otherwise if: (a) the expert’s scientific, technical, or
              other specialized knowledge is beyond that possessed by the
              average layperson; (b) the expert’s scientific, technical, or
              other specialized knowledge will help the trier of fact to
              understand the evidence or to determine a fact in issue; and
              (c) the expert’s methodology is generally accepted in the
              relevant field.




       [J-92A-2019, J-92B-2019, J-92C-2019, J-92D-2019 and J-92E-2019] - 16
Pa.R.E. 702 (emphasis added).

       The requirement that the expert’s methodology be generally accepted is commonly

referred to as the Frye test. First announced in Frye v. United States, 293 F. at 1013, it

was adopted by this Court in Pennsylvania in Topa. In Grady v. Frito Lay, Inc., 839 A.2d

1038, 1047 (Pa. 2003), we clarified that the Frye rule “applies to an expert’s method, not

his conclusions.” As artfully stated by former Chief Justice Cappy,

              The Frye standard is limited to an inquiry into whether the
              methodologies by which the scientist has reached her
              conclusions have been generally accepted in the scientific
              community... . It restricts the scientific evidence which may
              be admitted as it ensures that the proffered evidence results
              from scientific research which has been conducted in a
              fashion that is generally recognized as being sound, and is
              not the fanciful creations of a renegade researcher. Yet, such
              a standard is not senselessly restrictive for it allows a scientist
              to testify as to new conclusions which have emerged during
              the course of properly conducted research.

Blum, 764 A.2d at 9 (Cappy, C.J., dissenting) (emphasis in original). The proponent of

the admission of expert scientific evidence bears the burden of establishing all of the

elements supporting its admission, including the general acceptance of the methodology

employed in the relevant scientific community. Grady, 839 A.2d at 1045; Betz, 44 A.3d

at 54. While the methodologies employed by the expert must be generally accepted, the

conclusions reached from those applications need not also be generally accepted. Trach

v. Fellin, 817 A.2d 1102, 1112 (Pa. Super. 2003) (en banc).

       The Court in Grady made clear that whether a methodology is generally accepted

in the relevant scientific community is a determination that has to be made based on the

testimony of the scientists in that community, not upon any scientific expertise of judges.

              One of the primary reasons we embraced the Frye test in
              Topa was its assurance that judges would be guided by



       [J-92A-2019, J-92B-2019, J-92C-2019, J-92D-2019 and J-92E-2019] - 17
              scientists when assessing the reliability of a scientific method.
              See Topa, 369 A.2d at 1281 (quoting United States v.
              Addison, 498 F.2d 741, 744 (D.C.Cir. 1974)). Given the ever-
              increasing complexity of scientific advances, this assurance is
              at least as compelling today as it was in 1977, when we
              decided that case. We believe now, as we did then, that
              requiring judges to pay deference to the conclusions of those
              who are in the best position to evaluate the merits of scientific
              theory and technique when ruling on the admissibility of
              scientific proof, as the Frye rule requires, is the better way of
              insuring that only reliable expert scientific evidence is
              admitted at trial.

Grady, 839 A.2d at 1044–45; see also id. at 1045 (“This does not mean, however, that

the proponent must prove that the scientific community has also generally accepted the

expert's conclusion. … This, in our view, is the sensible approach, for it imposes

appropriate restrictions on the admission of scientific evidence, without stifling creativity

and innovative thought.”).6

       Relatedly, with respect to causation issues, the Superior Court has offered the

following:

              Judges, both trial and appellate, have no special competence
              to resolve the complex and refractory causal issues raised by


6 In Betz, this Court described the trial court’s role in a Frye hearing as deciding whether
“an expert witness has … applied accepted scientific methodology in a conventional way
in reaching his or her conclusions.” 44 A.3d at 53. As noted by the concurring Justice,
this language could be viewed as interjecting an element of the Daubert standard into our
otherwise steadfast adherence to Frye’s teaching that the expert’s methodology be
“generally accepted in the relevant field.” Concurring Op. at 15 n.13. The dissenting
Justice outright disagrees with the notion that the “conventional fashion” language was
used in Betz to redefine Frye’s general acceptance standard. Instead, the dissenting
Justice indicates that this terminology was used only to identify novel science for the
purpose of determining whether to conduct a Frye hearing. Dissenting Op. at 14-16.

       Accepting both the concurring Justice’s view that the phraseology may be
confusing and the dissenting Justice’s opinion that its use was not intended to modify the
Frye general acceptance standard, we will not use the “conventional fashion” language
in our discussion. Here, the novelty of the science has been conceded by Appellee, who
did not appeal the Superior Court’s determination that the science was novel.

       [J-92A-2019, J-92B-2019, J-92C-2019, J-92D-2019 and J-92E-2019] - 18
               the attempt to link low-level exposure to toxic chemicals with
               human disease. On questions such as these, which stand at
               the frontier of current medical and epidemiological inquiry, if
               experts are willing to testify that such a link exists, it is
               for the jury to decide whether to credit such testimony.

Trach, 817 A.2d at 1117 (emphasis added) (quoting Ferebee v. Chevron Chemical Co.,

736 A.2d 1529, 1534 (D.C. Cir. 1984)).


Issue One: 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?

       For their first issue on appeal, the Appellants contend that the Superior Court erred

in ruling that the trial court had improperly exceeded its boundaries by reviewing in detail

the studies that Dr. Brautbar relied upon in reaching his expert opinions. The Appellants

posit that the Superior Court improperly held that in Frye proceedings trial courts are not

“gatekeepers,” as that is precisely the role that they play. Appellants’ Brief at 21 (citing

Blum ex rel. Blum v. Merrell Dow Pharmeceuticals, Inc., 705 A.2d 1314, 1322 (Pa. Super.

1997) (“[T]he judge as gatekeeper decides whether the expert is offering sufficiently

reliable, solid, trustworthy evidence.”)), affirmed, 764 A.2d 1 (Pa. 2000). According to the

Appellants, in past cases this Court has approved of careful review of the studies and

evidence relied upon by an expert to assess relevance and reliability. Appellants’ Reply

Brief at 5-8 (citing, e.g., Betz).

       In contrast, the Executor supports the Superior Court’s contention that trial courts

are not “gatekeepers.” The Executor claims that the Superior Court did not rule that a

trial court may not review studies or other evidence relied upon by an expert. Instead,



        [J-92A-2019, J-92B-2019, J-92C-2019, J-92D-2019 and J-92E-2019] - 19
the Executor contends that rather than merely reviewing the studies cited by Dr. Brautbar,

the trial court made a number of bald assertions regarding the relevance and validity of

said studies to Dr. Brautbar’s proposed scientific opinions. Executor’s Brief at 4. The

Executor insists that the trial court, by analyzing the scientific literature on its own, “delved

into an area beyond the training and experience of judges and lawyers and substituted

its analysis of the scientific literature for the analysis that was conducted by [Executor’s]

experts.” Id. at 7.

       Whether we refer to the role of the trial court in a Frye contest as that of a

“gatekeeper” is not consequential. What is of consequence is the role that the trial court

plays during Frye proceedings. A careful review of our prior Frye decisions makes clear

that it is the trial court’s proper function to ensure that the expert has applied a generally

accepted scientific methodology to reach his or her scientific conclusions. To fulfill this

function, the trial court must be guided by scientists in the relevant field, including the

experts retained by the parties in the case and any other evidence of general acceptance

presented by the parties (e.g., textbooks). Conversely, trial courts may not question the

merits of the expert’s scientific theories, techniques or conclusions, and it is no part of the

trial court’s function to assess whether it considers those theories, techniques and/or

conclusions to be accurate or reliable based upon the available facts and data. As is

plainly set forth in Rule 702(c), the trial court’s role is strictly limited to determining whether

“the expert’s methodology is generally accepted in the relevant field.” Pa.R.E. 702(c).

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




        [J-92A-2019, J-92B-2019, J-92C-2019, J-92D-2019 and J-92E-2019] - 20
agrees with the expert’s application of those methodologies or whether the expert’s

conclusions have sufficient factual support.7 Those are questions for the jury to decide.

       Judges typically have no specialized training that qualifies them to weigh in on the

expert’s resolution of the highly complex issues involved in the determination of the

causality of human disease resulting from exposure to specific toxins. By requiring the

scientists addressing those issues to utilize generally accepted methodologies, the trial

court conducting a Frye hearing ensures that the jury receives scientific opinion that is

the result of sound research, while simultaneously leaving sufficient flexibility for new

research to arrive at new conclusions previously uncredited.

       Based upon our review, we must agree with the Superior Court’s assessment that

the trial court’s Frye inquiry was at times “overly expansive.” Walsh, 191 A.3d at 844.

For example, the trial court rejected as scientifically unacceptable “animal studies, test-

tube studies and studies that include significant limiting language as to the applicability of

their results to causation theories.”8 Trial Court Opinion, 10/5/2016, at 12-13. According


7  To the extent that Pennsylvania trial courts conduct an “essential review for reliability,”
Dissenting Op. at 11, that review may consist only of establishing that the expert utilized
generally accepted methodologies in reaching his or her scientific conclusions. Under
Frye, requiring that an expert employ generally accepted methodologies is, in and of itself,
the means by which Pennsylvania courts ensure that only reliable scientific evidence is
presented to juries. See, e.g., Topa, 369 A.2d at 1282 (“The requirement of general
acceptance in the scientific community assures that those most qualified to assess the
general validity of a scientific method will have the determinative voice.”); Grady, 839 A.2d
at 1045 (“We believe now, as we did then, that requiring judges to pay deference to the
conclusions of those who are in the best position to evaluate the merits of scientific theory
and technique when ruling on the admissibility of scientific proof, as the Frye rule requires,
is the better way of insuring that only reliable expert scientific evidence is admitted at
trial.”).
8 The Appellants point out that this Court in Betz discounted the usefulness of these types
of evidence in a substantial cause analysis. Betz, 44 A.3d at 55. That assessment was,
however, obviously based upon the evidence of record (including expert deposition
testimony) in that case, and the manner in which the expert was attempting to use such

       [J-92A-2019, J-92B-2019, J-92C-2019, J-92D-2019 and J-92E-2019] - 21
to the trial court, it is not generally accepted methodology “to select portions of studies

that favor a certain outcome while ignoring direct statements against that outcome within

the same article.” Id. In so ruling, however, the trial court did so unilaterally, without

citation to any authority or to the voluminous expert deposition testimony in the certified

record. Whether it was in accordance with generally accepted methodology to rely upon

animal and/or test tube studies of the sorts cited on Dr. Brautbar’s Exhibit C (evaluating

the genotoxicity of the active ingredients in the Appellants’ products) constituted a

scientific judgment that must be guided by the experts, not a trial court. Similarly, whether

Dr. Brautbar could rely upon articles containing limiting language would depend upon the

precise nature of that limiting language and the purpose for which Dr. Brautbar was relying

upon it. Again, it was not the province of the trial court, but rather the scientists (including

Dr. Brautbar), to guide this decision. The trial court’s role was limited to determining

whether Dr. Brautbar reached his scientific conclusions by applying generally accepted

scientific methodologies.

       The trial court likewise found it unacceptable for Dr. Brautbar to rely on studies that

did not reach the same ultimate conclusion reached by Dr. Brautbar, rejecting studies that

did not identify a direct causal link between AML and a particular pesticide manufactured

by one of the Appellants. The trial court acknowledged that Dr. Brautbar’s opinion relied

upon an indirect link between pesticides and AML, specifically that pesticide exposures

result in specific chromosomal abnormalities (abnormalities of the fifth and seventh



(…continued)
studies when formulating his conclusions. In baldly rejecting “animal studies, test-tube
studies and studies that include significant limiting language,” the trial court did not refer
to the certified record in this case or to any other authority in support of its pronouncement.


        [J-92A-2019, J-92B-2019, J-92C-2019, J-92D-2019 and J-92E-2019] - 22
chromosomes), which in turn start the process to carcinogenicity that leads to leukemia

(including AML). Brautbar Initial Report, 2/17/2014, at 22. After reviewing the studies Dr.

Brautbar cited in support of his conclusions, however, the trial court rejected, as

unsupported, Dr. Brautbar’s scientific conclusion that “[c]hromosomal changes are like

fingerprints of prior exposure” to certain types of chemicals, including pesticides and/or

benzene. Id. at 21.

      Dr. Brautbar’s conclusion that specific patterns of chromosomal aberrations are

like “fingerprints” was an important component in his product specific analyses by

demonstrating that Walsh’s exposure to pesticides and benzene was a substantial

contributing cause of his AML, as per the detailed information in Exhibits B and C of his

report. It was also important to his differential diagnosis, as it is his contention that

“fingerprints” in chromosomal aberrations excluded a finding that Walsh’s’ AML was

idiopathic (without any known external cause). The trial court noted that Dr. Brautbar had

relied upon (among others) a study by Cuneo that provided some support for the

chromosomal aberrations theory based upon a comparison of individuals with AML

divided into two groups (those exposed to pesticides and those not exposed). Cuneo

concluded that “patients exposed to pesticides had the same recurring chromosomal

aberrations and cytological features, which were different from those found in the

unexposed group.” Brautbar Initial Report. 2/17/2014, at 24 (citing Ontario College of

Family Physicians, Leukemia (Chapter 5), Pesticides Literature Review (April 23, 2004),

49-50) (reviewing Cuneo, A., et al., Morphologic, Immunologic and Cytogenetic Studies

in Acute Myeloid Leukemia Following Occupational Exposure to Pesticides and Organic

Solvents, Leuk Res. 16:789-796 (1992))).




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       The trial court, however, noted that Cuneo’s study did not show that individuals

with AML in the exposed group always showed chromosomal aberrations to the fifth and

seventh chromosomes, as the cytogenetic results of a few members of the exposed group

did not demonstrate the identified pattern of aberrations. Trial Court Opinion, 10/5/2016,

at 18-19. According to the trial court, this proved that there was no “fingerprint” of AML

caused by exposure to pesticides and/or benzene. Id. In reaching this conclusion, the

trial court did not consider Dr. Brautbar’s deposition testimony, in which he explained at

some length that Cuneo had used an older methodology for the identification of members

of the exposed and unexposed groups and that the use of a newer methodology in fact

demonstrates a chromosomal fingerprint in Cuneo’s exposed group.                    Brautbar

Deposition, 5/13/2014, at 364-79.

       Importantly, the trial court’s rejection of Dr. Brautbar’s “fingerprint” conclusion was

based solely upon its own analysis of the scientific studies proffered by Dr. Brautbar and

not on any review of the methodology that Dr. Brautbar was utilizing to reach his

conclusion.9 A focus on his methodology would have included consideration of both Dr.



9  The Appellants contend that in past cases this Court has approved of trial courts
conducting their own intensely granular reviews of the scientific evidence offered by
experts in support of their opinions. The Appellants argue that in Betz, the Court
recognized that the trial court had considered “the testimony of the witnesses, voluminous
scientific literature, and numerous legal authorities proffered in support of the plaintiffs’
and defendants’ respective positions.” Betz, 44 A.3d at 39 (citing In re Toxic Substance
Cases, 2006 WL 2404008, at *2 (C.P.Allegheny, Aug. 17, 2006)). In so doing, however,
and in contrast to the trial court in the case before us, this Court emphasized that the trial
court’s systemic review of the evidence was for the express purpose of deciding whether
the expert witness had utilized a generally accepted methodology. Id. at 39 (“Focusing
upon methodology, Judge Colville found no support for the any-exposure theory of
specific causation in any of the sources upon which Dr. Maddox relied.”) (emphasis
added); id. at 40 (“Rather, [the trial court] agreed with the defendants' experts that Dr.
Maddox's methodology was plagued by unwarranted liberties and logical errors.”
(emphasis added); id. at 53 (“[The trial court] spent considerable time listening to the

       [J-92A-2019, J-92B-2019, J-92C-2019, J-92D-2019 and J-92E-2019] - 24
Brautbar’s deposition testimony as well as that of the Appellants’ experts. Dr. Marshall

Lichtman, for example, testified at his deposition that up to 85% of AML cases are

idiopathic and that about half of them have no distinct pattern of chromosomal

aberrations. Lichtman Deposition at 28. Dr. Lichtman further testified that in comparison

to the Cuneo study, in which 21 patients were in the exposed group, Dr. Brautbar had not

considered at least four larger subsequent studies (with more than 5,500 patients) which

found cytogenetic abnormalities are not present in about half of de novo AML cases, and

that as a result one cannot use the appearance of chromosomal abnormalities to reach

the conclusion that the AML case must have been externally caused (e.g., by exposure

to pesticides or benzene). Id. at 49-50. According to Dr. Lichtman, Dr. Brautbar did not

follow a generally accepted scientific methodology by relying only on those studies that

supported his conclusions while ignoring much larger studies that did not do so. Id.

      In their Frye motions filed in the trial court, the Appellants raised this issue –

whether Dr. Brautbar applied a generally accepted methodology to arrive at his

cytogenetic “fingerprint” conclusion. See Defendants’ Joint Brief in Support of Motions to

Exclude Expert Testimony of April Zambelli-Weiner and Nachman Brautbar, 3/9/2016, at

2-5. The trial court issued no ruling on the issue. The Appellants also questioned whether

Dr. Brautbar and/or Dr. Zambelli-Weiner utilized a generally accepted methodology when

they applied the Bradford Hill criteria to establish causation to “pesticides-as-a-class”

rather than to their individual products, by applying certain of the Bradford Hill factors




(…continued)
attorneys' arguments but was unable to discern a coherent methodology supporting the
notion that every single fiber from among, potentially, millions is substantially causative
of disease.”) (emphasis added).

       [J-92A-2019, J-92B-2019, J-92C-2019, J-92D-2019 and J-92E-2019] - 25
contrary to the ways in which Sir Bradford Hill intended for them to be applied (and

ignoring others entirely), and by failing to identify any epidemiological studies

demonstrating a causal association between AML and their specific products before

engaging in the Bradford Hill methodology at all. Id. The Appellants contested Dr.

Brautbar’s methodology of opining on specific causation without first establishing the

specific dose at which their products could cause AML. Id. The Appellants contended

that Drs. Brautbar and Zambelli-Weiner did not follow a generally accepted methodology

by “cherry-picking” studies that supported their conclusions while ignoring other studies

that did not. Id. Finally, the Appellants contested Dr. Brautbar’s application of the

differential diagnosis methodology when he failed to rule out a known cause of AML

(obesity). Id.

       The trial court issued no rulings on any of these Frye challenges. To the contrary,

in its initial opinion granting the Appellants’ Frye motions, the trial court did not even

mention the Bradford Hill criteria or indicate that the Executor’s experts (and at least one

of the Appellants’ experts) were employing this methodology. In its subsequent Rule

1925(a) opinion, the trial court merely indicated that Dr. Brautbar’s use of the Bradford

Hill methodology required reliance upon peer-reviewed research, which it had already

concluded “did not stand for the conclusions that Dr. Brautbar cited them for.” Rule

1925(a) Opinion, 12/22/2016, at 5. By questioning the judgment of the Executor’s experts

and the reliability of their scientific conclusions, rather than focusing on whether the

Executor satisfied his burden of proof that Drs. Zambelli-Weiner and Brautbar formed

their opinions by application of methodologies that are generally accepted in the relevant

fields of study, the trial court abused its discretion. Accordingly, we agree with the




       [J-92A-2019, J-92B-2019, J-92C-2019, J-92D-2019 and J-92E-2019] - 26
Superior Court’s decision to vacate the trial court’s orders granting the Appellants’ Frye

motions and entering summary judgment. On remand, the Appellants should be afforded

the opportunity to renew their Frye motions so that the relevant issues can be addressed.


Issue Two: 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 plaintiff's
           burden to show product-specific causation of plaintiff's specific
           injury?

       For their second issue on appeal, the Appellants argue that the Superior Court

held that experts can satisfy their burden under the Frye test by and through the

unrestricted use of extrapolation. The Appellants insist that the Superior Court held that

establishing a causal link between cancer and long-term exposure to “pesticides-as-a-

class” is sufficient to support a causation decision regarding exposure to the specific

pesticide products at issue in the case. The Appellants contend that under the Superior

Court’s analysis, if an expert can cite to literature suggesting that a class of products may

cause a disease, then that expert has met his or her burden under Frye to opine that any

particular product in that class caused the disease, regardless of the diversity between

the various types of products within that class. According to the Appellants, the Superior

Court’s ruling ignores this Court’s ruling in Betz, which established strong limitations on

the use of extrapolation in substantial cause analyses and effectively eliminates the

plaintiff’s the burden to show product-specification.

       The Appellants have misread the Superior Court’s opinion, as it does not in any

respect bless the unfettered use of extrapolation in a substantial cause analysis and it did

not eliminate a plaintiff’s burden to show product-specification. To the contrary, the




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Superior Court’s principal focus was directed to the trial court’s rejection of studies cited

by Dr. Brautbar based upon its own conclusion that his reliance on them was not

scientifically acceptable, either because the study did not identify a direct causal link

between a particular Appellant’s product and AML or because it reached a conclusion

contrary to that ultimately reached by Dr. Brautbar. Walsh, 191 A.3d at 845-46. The trial

court, in reviewing and analyzing the cited scientific articles, had “impermissibly set

himself up ‘as a super expert in the field of medicine,’” and had thus added an extra “layer

to the generally accepted methodology requirement” that is not any part of a proper Frye

analysis. Id. In response, the Superior Court properly indicated that the “absence of a

treatise or study directly on point goes to the weight, not to the admissibility, of expert

testimony,” id. at 847, and further stated that an expert is not required to parrot the

conclusions of study authors.” Id. at 846. The Superior Court likewise rejected any notion

that a proper Frye causal analysis must include an epidemiological study demonstrating

an increased incidence of AML after substantial exposures to their specific products (or

the active ingredients in their specific products). Id. at 847-48 (“For purposes of Frye, an

expert need not rely on studies that mirror the exact facts under consideration.”).

       In Trach, the Superior Court described extrapolation as a logical method used “to

estimate the value of a variable outside its tabulated or observed range” or “to infer (that

which is not known) from that which is known.” Trach, 817 A.2d at 1114-16 (citing

Donaldson v. Central Illinois Public Service Co., 767 N.E.2d 314, 328–329 (Ill. 2002)

(“Extrapolation is commonly used by scientists in certain limited instances ..., for example,

when the medical inquiry is new or the opportunities to examine a specific cause and

effect relationship are limited; when the number of cases limits study of the disease; or




       [J-92A-2019, J-92B-2019, J-92C-2019, J-92D-2019 and J-92E-2019] - 28
… when ethical considerations prevent exposing individuals to a toxic substance for

research purposes.”)). Given the breadth of these definitions of the term, except in those

rare circumstances in which a perfectly comparable study supports a direct causal

relationship between a particular agent and a disease, virtually every expert opinion on

substantial causation will likely contain instances of the use of extrapolation.         The

Executor here does not contend that Drs. Zambelli-Weiner and Brautbar did not engage

in the use of any extrapolation in formulating the opinions set forth in their expert reports.

To the contrary, at his deposition Dr. Brautbar forthrightly admitted to his use of

extrapolation in at least one respect, namely that “[e]xtrapolation from animal studies,

extrapolation from cell studies, extrapolation from human cell studies to disease

causation” are part of ”the “mechanistic aspects to understanding causation of disease.

Brautbar Deposition, 5/13/2014, at 30-31).

        Importantly for present purposes, however, our review of the expert reports of Drs.

Zambelli-Weiner and Brautbar does not reflect that either of them used extrapolation in

the manner now complained of by Appellants. Specifically, while both experts employed

the Bradford Hill criteria to establish a causal link between cancer (or AML) and long-term

exposure to pesticides, neither expert opined that this link wholly constituted product-

specific causation between cancer and long-term exposure to the Appellants’ specific

pesticide products. In her expert report, Dr. Zambelli-Weiner offered no opinions with

regard to any of the Appellants’ specific products.10 To the contrary, at her deposition


10   Dr. Zambelli-Weiner’s expert report sets forth three opinions:
        1. Mr. Walsh had cumulative lifetime exposure days to pesticides consistent
        with exposure levels associated with increased risk of leukemia, and AML
        specifically, in published peer-reviewed literature.


         [J-92A-2019, J-92B-2019, J-92C-2019, J-92D-2019 and J-92E-2019] - 29
she expressly refused to answer questions about whether any of the Appellants’ specific

products cause cancer/AML. Zambelli-Weiner Deposition, 9/23/2014, at 107-08; ("I was

not charged with evaluating the association of any particular product ... with leukemia.");

Id., 9/24/2014, at 355 ("I wasn't tasked with studying chlorpyrifos specifically.").

       With respect to the Appellants’ Frye motions, we note that the trial court issued no

ruling with respect to whether Dr. Zambelli-Weiner’s failure to opine on whether the

Appellants’ specific products may cause leukemia precludes her use as an expert on

general causation at trial,11 and the Superior Court likewise did not address this issue.

As a result the Superior Court’s opinion, contrary to the assertions of Appellants, did not

eliminate the plaintiff’s burden to show product-specification. See Rost v. Ford Motor Co.,

151 A.3d 1032, 1044 (Pa. 2016) (Pennsylvania law requires that “to create a jury question,



(…continued)
     2. It is my opinion, to a reasonable degree of medical certainty, that
     exposure to pesticide formulations, individually or in combination, is
     causally related to an increased risk of cancer in humans exposed to them.
       3. It is my opinion, to a reasonable degree of scientific certainty, that
       exposure to organophosphate pesticide formulations, individually or in
       combination, is causally related to an increased risk of leukemia in humans
       exposed to them.
Zambelli-Weiner Report, 7/18/2012, at 13-15.
11  The trial court stated that “I find that Dr. Zambelli-Weiner’s general causation opinion
regarding pesticides as a class is not in accordance with generally accepted scientific
methodology because it fails to account for variations in composition of the universe of
chemicals, compounds, or the like that might be considered a “pesticide.” Trial Court
Opinion, 10/5/2016, at 19. The trial court offered this observation as its own opinion,
however, as it was not accompanied by citation to any scientific authority in the record in
its support. Moreover, the remark must be considered to be mere dicta, as the trial court
offered it only after having rejected Dr. Brautbar’s opinion on specific causation opinions.
Id. (“Because Dr. Brautbar’s specific causation opinions are not formed using generally
accepted scientific methodology, the viability of Dr. Zambelli-Weiner’s general causation
opinions is not material.”).


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a plaintiff must adduce evidence that exposure to defendant’s [product] was sufficient …

to support a jury’s finding that defendant’s product was substantially causative of the

disease.”).

       As indicated, Dr. Brautbar also applied the Bradford Hill criteria to establish a

causal link between AML and long-term exposure to pesticides. He did not extrapolate

from this finding that because pesticides increase the risk of contracting AML that

Appellants’ specific products likewise increase this risk. To the contrary, he disclaimed

any use of this type of extrapolation, stating in his initial expert report “that some

pesticides cause [AML] does not necessarily mean that all pesticides cause this disease.”

Brautbar Initial Report, 2/17/2014, at 18. He then proceeded to conduct product-specific

analyses of each product manufactured by the Appellants, evaluating the chemical

components of each of the pesticides individually and concluding that each of them

contained chemicals that were genotoxic or caused DNA damage, and thus are

carcinogenic. Id. at 21-23 and Exhibits B and C.

       The Superior Court neither blessed the indiscriminate use of extrapolation nor

adopted the Appellants’ contention that its opinion may fairly be read to hold that

establishing a causal link between cancer and long-term exposure to pesticides is

sufficient to support a causation decision regarding exposure to a defendant’s specific

product; rather, the Superior Court properly indicated that an expert need not rely on

studies mirroring the exact facts under consideration, as a synthesis of various legitimate

studies which reasonably permits experts’ conclusions may be sufficient for purposes of

Frye. Walsh, 191 A.3d at 847-48. In our decision in Rost, this Court reaffirmed that the




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plaintiff has a burden to show product-specification. See Rost, 151 A.3d at 1044. The

Superior Court’s opinion may not be fairly read to alter that burden in any respect.


Issue Three: Did the Superior Court majority commit reversible error in
             concluding that the trial court erred without explaining how it
             abused its discretion because of manifest unreasonableness,
             partiality, prejudice, bias, ill-will or such lack of support from
             the evidence or the record so as to be clearly erroneous?

       The Appellants argue that although the Superior Court found that the trial court

erred, “it never actually stated that he abused his discretion.” Appellants’ Brief at 59. The

Appellants insist that the Superior Court failed to identify how the trial court erred and

further allege that the Superior Court, rather than applying the abuse of discretion

standard, instead substituted its own judgment for that of the trial court. Id.

       We disagree. It is unnecessary for an appellate court to use any “magic language”

when ruling that a lower court abused its discretion. It is enough for the appellate court

to explain how the lower court abused its discretion. In our view, the Superior Court

plainly set forth numerous abuses of discretion by the trial court, including its review of

the scientific literature at a granular level to make its own bald judgments about which

studies relied upon by Dr. Brautbar were scientifically acceptable, relevant and/or

supportive of his conclusions. Walsh, 191 A.3d at 844-45. As the Superior Court correctly

recognized, “[t]hat is not the proper role of the trial court in a Frye inquiry.” Id. at 844.

       As such, the Superior Court found the trial court’s consideration of the Appellants’

Frye motions to be flawed in multiple respects and vacated the trial court’s decision on

that basis. We thus conclude that the Superior Court properly applied its standard of

review.




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      The order of the Superior Court is affirmed. On remand to the trial court, the

Appellants should be afforded the opportunity to renew their Frye motions for the reasons

addressed in this Opinion.

      Justices Dougherty, Wecht and Mundy join the opinion.

      Justice Wecht files a concurring opinion.

      Justice Baer files a concurring and dissenting opinion.

      Chief Justice Saylor files a dissenting opinion in which Justice Todd joins.




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