[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, 

EXECUTOR OF THE ESTATE OF 

THOMAS J. WALSH, DECEASED

v.

BASF CORPORATION; BAYER 

CORPORATION D/B/A BAYER 

CROPSCIENCE, L.P., AND BAYER 

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.

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No. 14 WAP 2019

Appeal from the Order of the Superior 

Court entered June 20, 2018 at No. 

1661 WDA 2016 vacating the Order of 

the Court of Common Pleas of 

Allegheny County entered October 

14, 2016 at No. GD 10-018588, and 

remanding

ARGUED: October 16, 2019

RICHARD THOMAS WALSH, 

EXECUTOR OF THE ESTATE OF 

THOMAS J. WALSH, DECEASED

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No. 15 WAP 2019

Appeal from the Order of the Superior 

Court entered June 20, 2018 at No. 
[J-92A-2019, J-92B-2019, J-92C-2019, J-92D-2019 and J-92E-2019] - 2

v.

BASF CORPORATION; BAYER 

CORPORATION D/B/A BAYER 

CROPSCIENCE, L.P., AND BAYER 

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

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1661 WDA 2016, vacating the Order 

of the Court of Common Pleas of 

Allegheny County entered October 

14, 2016 at No. GD 10-018588, and 

remanding

ARGUED: October 16, 2019

RICHARD THOMAS WALSH, 

EXECUTOR OF THE ESTATE OF 

THOMAS J. WALSH, DECEASED

v.

BASF CORPORATION; BAYER 

CORPORATION D/B/A BAYER 

CROPSCIENCE, L.P., AND BAYER 

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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No. 16 WAP 2019

Appeal from the Order of the Superior 

Court entered June 20, 2018 at No. 

1661 WDA 2016, vacating the Order 

of the Court of Common Pleas of 

Allegheny County entered October 

14, 2016 at No. GD 10-018588, and 

remanding

ARGUED: October 16, 2019
[J-92A-2019, J-92B-2019, J-92C-2019, J-92D-2019 and J-92E-2019] - 3

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.

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RICHARD THOMAS WALSH, 

EXECUTOR OF THE ESTATE OF 

THOMAS J. WALSH, DECEASED

v.

BASF CORPORATION; BAYER 

CORPORATION D/B/A BAYER 

CROPSCIENCE, L.P., AND BAYER 

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

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No. 17 WAP 2019

Appeal from the Order of the Superior 

Court entered June 20, 2018 at No. 

1661 WDA 2016, vacating the Order 

of the Court of Common Pleas of 

Allegheny County entered October 

14, 2016 at No. GD 10-018588, and 

remanding

ARGUED: October 16, 2019
[J-92A-2019, J-92B-2019, J-92C-2019, J-92D-2019 and J-92E-2019] - 4

RICHARD THOMAS WALSH, 

EXECUTOR OF THE ESTATE OF 

THOMAS J. WALSH, DECEASED

v.

BASF CORPORATION; BAYER 

CORPORATION D/B/A BAYER 

CROPSCIENCE, L.P., AND BAYER 

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

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No. 18 WAP 2019

Appeal from the Order of the Superior 

Court entered June 20, 2018 at No. 

1661 WDA 2016, vacating the Order 

of the Court of Common Pleas of 

Allegheny County entered October 

14, 2016 at No. GD 10-018588, and 

remanding

ARGUED: October 16, 2019

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] - 5

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. 
[J-92A-2019, J-92B-2019, J-92C-2019, J-92D-2019 and J-92E-2019] - 6

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] - 7

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.
[J-92A-2019, J-92B-2019, J-92C-2019, J-92D-2019 and J-92E-2019] - 8

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 
[J-92A-2019, J-92B-2019, J-92C-2019, J-92D-2019 and J-92E-2019] - 9

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 
[J-92A-2019, J-92B-2019, J-92C-2019, J-92D-2019 and J-92E-2019] - 10

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.
[J-92A-2019, J-92B-2019, J-92C-2019, J-92D-2019 and J-92E-2019] - 11

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.” ZambelliWeiner 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-ofthe-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 
[J-92A-2019, J-92B-2019, J-92C-2019, J-92D-2019 and J-92E-2019] - 12

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 
[J-92A-2019, J-92B-2019, J-92C-2019, J-92D-2019 and J-92E-2019] - 13

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] - 14

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 
[J-92A-2019, J-92B-2019, J-92C-2019, J-92D-2019 and J-92E-2019] - 15

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.
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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 
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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 everincreasing 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.
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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, 
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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 
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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, testtube 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] - 22

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.
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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 
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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).
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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 
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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-aclass” 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] - 29

... 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 productspecific 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.
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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.