[J-92A-E-2019][M.O. - Donohue, J.]

IN THE SUPREME COURT OF PENNSYLVANIA

 WESTERN DISTRICT

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 6/20/18 at No. 1661 WDA 

2016 vacating the order of the Court of 

Common Pleas of Allegheny County 

entered 10/14/16 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 6/20/18 at No. 1661 WDA 

2016 vacating the order of the Court of 
[J-92A-E-2019][M.O. – Donohue, J.] - 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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Common Pleas of Allegheny County 

entered 10/14/16 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 

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No. 16 WAP 2019

Appeal from the Order of the Superior 

Court entered 6/20/18 at No. 1661 WDA 

2016 vacating the order of the Court of 

Common Pleas of Allegheny County 

entered 10/14/16 at No. GD 10-018588 

and remanding

ARGUED: October 16, 2019
[J-92A-E-2019][M.O. – Donohue, J.] - 3

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: 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.

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No. 17 WAP 2019

Appeal from the Order of the Superior 

Court entered 6/20/18 at No. 1661 WDA 

2016 vacating the order of the Court of 

Common Pleas of Allegheny County 

entered 10/14/16 at No. GD 10-018588 

and remanding

ARGUED: October 16, 2019
[J-92A-E-2019][M.O. – Donohue, J.] - 4

APPEAL OF: MONSANTO COMPANY

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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: BASF CORPORATION

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No. 18 WAP 2019

Appeal from the Order of the Superior 

Court entered 6/20/18 at No. 1661 WDA 

2016 vacating the order of the Court of 

Common Pleas of Allegheny County 

entered 10/14/16 at No. GD 10-018588 

and remanding

ARGUED: October 16, 2019

DISSENTING OPINION

CHIEF JUSTICE SAYLOR DECIDED: JULY 21, 2020

The majority deems it inconsequential whether or not this Court should 

denominate trial judges as gatekeepers relative to the admission of novel scientific 
[J-92A-E-2019][M.O. – Donohue, J.] - 5

evidence in Pennsylvania courtrooms. See Majority Opinion, slip op. at 20. Personally, 

however, I find this to be the clear purport of most of this Court’s decisions on the 

subject. My response to the majority opinion is set forth below. Since Justice Wecht 

has taken the opportunity, from a side position, to respond to my present remarks -- as 

well as to criticize the opinion that I authored in Betz v. Pneumo Abex LLC, 615 Pa. 504, 

44 A.3d 27 (2012) -- I have also included my reply to his opinion.

I. Reply to the Majority Opinion

On an appropriate motion, trial judges in Pennsylvania bear the obligation to 

screen novel scientific evidence for reliability before permitting such evidence to be put 

before jurors. See, e.g., Grady v. Frito-Lay, Inc., 576 Pa. 546, 557, 839 A.2d 1038, 

1044-45 (2003). This Court, like most others, has implemented this particular 

gatekeeping responsibility in light of the influential nature of expert testimony on 

complex subjects and the potential that distortions have to mislead laypersons. See

Betz, 615 Pa. at 544-47, 44 A.3d at 52-54; see also id. at 532 n.15, 44 A.3d at 44 n.15 

(quoting a cogent encapsulation by the Honorable Phyllis W. Beck in Blum v. Merrell 

Dow Pharms., Inc., 705 A.2d 1314, 1325 (Pa. Super. 1997), aff’d, 564 Pa. 3, 764 A.2d 1 

(Pa. 2000)); accord In re Accutane Litig., 191 A.3d 560, 589 (N.J. 2018) (explaining that 

“the gatekeeping function prevents the jury’s exposure to unsound science through the 

compelling voice of an expert” and “[d]ifficult as it may be, the gatekeeping role must be 

rigorous”).

For these reasons, I have previously expressed the concern that the Frye

standard should not be interposed in a way that deprives trial judges of the ability to 

screen expert opinions for sufficient reliability. See Commonwealth v. Smith, 606 Pa. 

127, 186, 995 A.2d 1143, 1177 (2010) (Saylor, J., concurring and dissenting) (“[I]f the 

Court is going to interpret Frye so narrowly as to justify the admission of speculative 
[J-92A-E-2019][M.O. – Donohue, J.] - 6

opinions, or opinions falsely couched in scientific literature, I believe the time has come 

for Pennsylvania to move to the Daubert standard.”). 

In this regard, to the degree that the majority opinion advocates that the Frye

standard is superior to approaches taken by other courts in the modern litigation 

environment, see, e.g., Majority Opinion, slip op. at 17-18, I respectfully disassociate 

myself from that view. Accord Grady v. Frito-Lay, Inc., 576 Pa. at 570, 839 A.2d at

1052 (Saylor, J., concurring) (“Concerning the Frye/Daubert debate, I take the position 

that the Frye rule is and remains the law of the Commonwealth, unless and until 

informed advocacy is presented that would favor a new direction, with due reference to 

the substantial body of information that has developed concerning the experience of the 

federal courts and others under Daubert.”). Significantly, I believe that there are 

benefits and drawbacks to each of the mainstream approaches, and I would reserve 

any assessment of the comparative merits to a setting in which the Court has the 

benefit of a developed analysis. See, e.g., Accutane, 191 A.3d at 583-95 (reflecting the 

Supreme Court of New Jersey’s recent refinement of the state’s standard governing the 

admissibility of novel expert opinions, upon close consideration of the available options).

In my view, Judge Wettick properly discharged his gatekeeping function in the 

present case. Upon review of scientific literature relied upon by Dr. Brautbar, Judge 

Wettick found that there were extensive, unexplained analytical gaps between the 

expert’s opinions and the material upon which he relied. See Walsh v. BASF Corp., No. 

GD-10-018588, slip op. at 2-19 (C.P. Allegheny Oct. 16, 2016); see also Walsh v. BASF 

Corp., No. GD-10-018588, slip op. at 2-6 (C.P. Allegheny Dec. 27, 2016). And that 

finding is amply supported by the record.
[J-92A-E-2019][M.O. – Donohue, J.] - 7

Indeed, the record support for Judge Wettick’s conclusion includes the testimony 

of Dr. Brautbar himself. For example, Dr. Brautbar acknowledged that dose response is 

a fundamental tenet of toxicology. See, e.g., See Deposition of Nachman Brautbar, 

M.D., dated May 15, 2014 at 836; accord Joseph V. Rodricks, Reference Guide on 

Exposure Science, REFERENCE MANUAL ON SCIENTIFIC EVIDENCE 507 (Fed. Judicial 

Center 3d ed. 2011) (“Ultimately the dose incurred by populations or individuals is the 

measure needed by health experts to quantify the risk of toxicity.”).1 He proceeded, 

however, to render opinions about substantial-factor causation relative to Mr. Walsh, 

while repeatedly conceding that he was both unable to identify any dose-response 

threshold for any of the fourteen products at issue in this case, see, e.g., N.B. at 798, 

and that he had no idea of the quantity of the dose experienced by Mr. Walsh for any 

particular product, see, e.g., id. at 300-301, 552. At least in many other courts, such 

testimony would plainly be regarded as unscientific and insufficient to establish 

substantial-factor causation.2 

 

1 The deposition of Dr. Brautbar spanned four days, but the pagination for the transcript 

was continuous. For convenience, the deposition is referred to hereinafter as “N.B. at 

__.”

2 See, e.g., McClain v. Metabolife Int’l, Inc., 401 F.3d 1233, 1241-42 (11th Cir. 2005) 

(relating that an expert’s failure to lay a reliable groundwork for assessing the doseresponse relationship in a toxic tort case “signals a methodological problem”); Burleson 

v. Tex. Dep’t of Criminal Justice, 393 F.3d 577, 587 (5th Cir. 2004) (highlighting that a 

causation opinion where the expert “fail[s] to conduct a dose assessment” produces “too 

great an analytical gap between the data and the opinion proffered” (citation omitted)); 

Mitchell v. Gencorp, Inc., 165 F.3d 778, 781 (10th Cir. 1999) (“[A] plaintiff must 

demonstrate the levels of exposure that are hazardous to human beings generally as 

well as the plaintiff’s actual level of exposure to the defendant’s toxic substance before 

he or she may recover.”); Allen v. Pa. Eng’g Corp., 102 F.3d 194, 199 (5th Cir. 1996) 

(“Scientific knowledge of the harmful level of exposure to a chemical, plus knowledge 

that the plaintiff was exposed to such quantities, are minimal facts necessary to sustain 

the plaintiffs’ burden in a toxic tort case.”); Yates v. Ford Motor Co., 113 F. Supp. 3d 

841, 861 (E.D.N.C. 2015) (“Rather than engage in any specific, meaningful comparison 

(continued...)
[J-92A-E-2019][M.O. – Donohue, J.] - 8

In this regard, Dr. Brautbar’s notion of substantiality, in terms of the duration of 

exposure, doesn’t conform at all to the legal standard, in that he defined the conception 

as merely being “not ridiculous, theoretical, or infinitesimal.” Id. at 776. Furthermore, 

numerous defense experts highlighted the unscientific nature of Dr. Brautbar’s analysis. 

See, e.g., Deposition of Scott D. Phillips, M.D., dated Jan. 12, 2016, at 32 (reflecting the 

testimony of a medical toxicologist that Dr. Brautbar’s methodology violated basic 

principles of toxicology in that he “simply stated that the dose was sufficient to cause his 

AML, which creates a circular logic reasoning kind of pathway”); Deposition of John 

Ross, Ph.D., dated Jan. 13, 2016, at 49 (remarking that Dr. Brautbar “repeated over and 

over again that it was the proximity, duration and frequency of exposure that allowed 

Mr. Walsh to be overexposed without providing a shred of evidence on what those 

were.”).3

 

(...continued)

of the scientific data with [the plaintiff’s] exposures, [the expert’s] opinions essentially 

attempt to overwhelm with statistics and studies, lacking guidance as to how a juror 

ought to apply them[, which] is not a reliable method, and it will not assist a jury.”).

I acknowledge that -- from my point of view at least -- a majority of this Court has 

previously sanctioned the admissibility of an expert opinion pertaining to substantialfactor causation on terms that would not meet (or even approach) the standards 

maintained in these other courts. See Rost v. Ford Motor Co., 637 Pa. 625, 666-76 & 

n.6, 151 A.3d 1032, 1057-63 & n.6 (2016) (Saylor, C.J., dissenting) (explaining, inter 

alia, that the relevant expert “made no attempt to even roughly quantify either the dose 

experienced by [the decedent at his place of employment] or his cumulative exposure or 

dose.”). That decision, however, arose in the discrete setting of an asbestosmesothelioma case, and it remains to be seen whether, or to what extent, the position 

will be transported beyond that unique arena.

3

In terms of Dr. Brautbar’s approach to the scientific studies, epidemiologist David H. 

Garabrant, M.D., testified that “scientists have an obligation to consider all relevant 

evidence and to weigh it.” Deposition of David H. Garabrant, M.D., dated Jan. 7, 2016, 

at 42. Consistent with Judge Wettick’s assessment, Dr. Garabrant explained that Dr. 

Brautbar neglected to do so and further failed to apply the Bradford Hill viewpoints 

(continued...)
[J-92A-E-2019][M.O. – Donohue, J.] - 9

The circularity inherent in Dr. Brautbar’s opinions is demonstrated throughout his 

deposition testimony. For example, after repeatedly asserting that the amount of 

exposure to each of the defendants’ products was substantial, the following interchange 

ensued between counsel for an appellant and Dr. Brautbar:

Q. [I]n terms of duration and the proximity and frequency, 

you don’t know how much of the chemical -- the 

pesticide he was exposed to for the duration or for how 

close he was to it or how frequently?

A. No. I don’t know.

* * *

Q. How -- how much [chlorothalonil] was Mr. Walsh 

exposed to during his work -- during his occupation?

A. He was exposed to a substantial dose, sufficient to 

contribute to his genotoxicity.

* * *

Q. But you can’t tell me how much besides saying 

substantial?

A. Well, substantial is how much. And it is based on the 

duration, proximity, and frequency.

 

(...continued)

which he invoked in a reliable manner. See id. at 101. Rather, Dr. Garabrant testified 

that Dr. Brautbar “cherry pick[ed].” Id. at 127. In particular, Dr. Brautbar “never 

mentions the absence of dose-response relationship in the studies that have examined 

it for the pesticides at issue. And so his claim that the dose-response data tends to 

support a causal relationship is not true for the pesticides at issue in this case and for 

leukemia.” Id. at 131; see also id. at 134 (asserting that Dr. Brautbar “misinterpreted a 

number of the [Bradford Hill viewpoints], he’s failed to support others, and he has 

invoked chemicals not at issue in this case and diseases not at issue in this case in 

support of his views”). Judge Wettick’s close review of some of the studies involved 

parallels this line of criticism.
[J-92A-E-2019][M.O. – Donohue, J.] - 10

Q. But you don’t know the dose.

A. That’s a dose. 

* * *

Q. Don’t you have to know the amount of the chemical for 

the duration and the proximity and the frequency to 

calculate the dose for an individual?

A. Are you asking me general, or are you asking --

Q. I’ll ask -- chlorothalonil specifically. For any of the 

pesticides involved in this case.

A. No.

Q. No? You don’t need to know the amount?

A. Well, the amount was substantial based on what I have 

described.

300-303.4

The record is replete with this sort of exchange, which is along the lines of what 

courts have denominated as unscientific ipse dixit (or assertions which are made but not 

proven). Cf. Gen. Elec. Co. v. Joiner, 522 U.S. 136, 146, 118 S. Ct. 512, 519 (1997)

(“[N]othing in . . . the Federal Rules of Evidence requires a district court to admit opinion 

evidence that is connected to existing data only by the ipse dixit of the expert.”). 

 

4 Although he repeatedly denied it, much of the purport of Dr. Brautbar’s testimony was 

that, because he found there to have been an effect on Mr. Walsh’s chromosomes that 

in his judgment could only be attributed to benzene or pesticides, Mr. Walsh must have 

experienced a sufficient dose from the defendants’ pesticides to have caused it. See,

e.g., N.B. at 511-512. As Appellants explain at length, this represents another example 

of circularity in Dr. Brautbaur’s reasoning. See, e.g., Joint Brief for Appellants Bayer 

Cropscience LP, Bayer Corp., Bayer Cropscience Holding Inc. & Dow Agrosciences 

LLC at 28.
[J-92A-E-2019][M.O. – Donohue, J.] - 11

Ultimately, Dr. Brautbar resorted to faulting the appellant companies for the lack of data 

underlying his opinions concerning substantial-factor causation. See, e.g., N.B. at 900 

(reflecting Dr. Brautbar’s response to an appellant’s attorney that, an “[e]xposure model 

can be made if I’m provided with some data from all of you of air monitoring, which 

wasn’t provided. So I’m going to throw this back to you.”). There is, of course, no 

suggestion on this record that this sort of burden-shifting rationale reflects a generally 

accepted scientific methodology.5

The majority’s holding appears to be that a trial judge must hew more closely to 

crediting or discrediting the competing expert testimony about what any particular study 

or studies say, rather than actually looking at the studies themselves in the Frye

context. See, e.g., Majority Opinion, slip op. at 25-26, 32. Respectfully, I believe this 

imposes an unreasonable constraint on the trial courts’ ability to perform the essential 

review for reliability. In this regard, I fail to see how judges can be expected to test 

competing opinions from experts while being constrained in their ability to review the 

opinions’ underpinnings. Accord Walsh v. BASF Corp., 191 A.3d 838, 849-50 (Pa. 

 

5 There is also ample evidentiary support for Judge Wettick’s rejection of Dr. Brautbar’s 

“fingerprints” theory, as lacking any grounding in appropriate scientific methodology. 

For example, and as the majority recognizes, a defense expert testified, consistent with 

Judge Wettick’s opinion, that this theory is wholly unsupported by the scientific 

literature. See Deposition of Marshall Lichtman, M.D., dated December 18, 2015, at 33-

34 (“I did not see any accepted methodology and I could not find any support for the 

statement in the material that Dr. Brautbar used to arrive at his opinions.”); id. at 35; id.

at 45 (explaining that “there is [scientific] agreement that there is no cytogenetic pattern 

that can allow you to determine if a patient was exposed to a chemical that might have 

played a role in causing their case of acute myelogenous leukemia” (emphasis added)); 

id. at 49-50 (“That’s a novel concept and, as far as I can tell, it’s pulled out of the air.”); 

id. at 76; accord Deposition of Michael I. Greenberg, M.D., dated Jan. 15, 2016, at 42-

43 (reiterating that there is no support in the published literature for Dr. Brautbar’s 

“fingerprints” opinion).
[J-92A-E-2019][M.O. – Donohue, J.] - 12

Super. 2018) (Bender, P.J.E., dissenting). And, upon such consideration, where the 

judge discerns a lack of appropriate scientific methodology, I cannot agree that it is 

inappropriate for him to so hold.

I also agree with Judge Wettick and Appellants that both of Appellee’s experts 

inappropriately extrapolated from “pesticides” as a product class -- including numerous 

pesticides that Mr. Walsh never used -- to Appellees’ specific products, with no analysis 

of whether the products were chemically, functionally, or toxicologically similar. Accord 

McClain, 401 F.3d at 1245-46 (explaining that ignoring differences in chemical structure 

“does not make for reliable opinions in toxic tort cases”). There is also abundant record 

evidence confirming that this form of extrapolation lacks general acceptance in the 

scientific community. See, e.g., Deposition of David H. Garabrant, M.D., dated Jan. 7, 

2016, at 36-37 (analogizing Dr. Zambelli-Weiner’s opinion to the rendering of a 

homogenous opinion with respect to the toxic effects of such diverse substances as “a 

shot of bourbon, purified water, sugar-sweetened beverages like soda, beer,” simply 

because all are beverages).6

 

6 As reflected above, I respectfully disagree with the majority’s pronouncement that Dr. 

Brautbar’s analysis was free from extrapolation in relevant regards. See Majority 

Opinion, slip op. at 29. Indeed, it is very difficult to understand Dr. Brautbar’s testimony 

as anything else besides extrapolation from a class to particular products when he had 

no idea of the dose-response threshold associated with any specific product, see e.g., 

N.B. at 798, nor any appreciation of the dose experienced by Mr. Walsh for any product, 

see, e.g., id. at 300-301, 552, 798.

Dr. Zambelli-Weiner also extrapolated severely, since her opinion that pesticides as a 

class cause leukemia, see, e.g., Deposition of April Zambelli-Weiner, Ph.D., dated Sept. 

23, 2014, at 74, can only be understood to apply to Appellees’ discrete products since 

they are pesticides, accord id. at 105 (reflecting Dr. Zambelli-Weiner’s explanation that 

her opinions “are related to pesticides as a class” and “to the extent that a product is a 

pesticide, it is included in that opinion”). And I agree with Judge Wettick that such a 

gross form of extrapolation lacks any basis in accepted scientific methodology. See 

Walsh, No. GD-10-018588, slip op. at 19 (C.P. Allegheny Oct. 16, 2016).
[J-92A-E-2019][M.O. – Donohue, J.] - 13

With regard to Dr. Zambelli-Weiner specifically, I find Judge Wettick’s 

assessment to be compelling that:

Dr. Zambelli-Weiner’s 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.” I find that failure 

to account for such an important variable is not in 

accordance with generally accepted scientific methodology.

Walsh v. BASF Corp., No. GD-10-018588, slip op. at 19 (footnote omitted); accord Joint 

Brief for Appellants Bayer Cropscience LP, Bayer Corp., Bayer Cropscience Holding 

Inc. & Dow Agrosciences LLC at 35 (“There was no evidence, including from Plaintiff’s 

experts, that, for example, citing studies about completely different products to support 

a causation opinion is conventional.”); see also id. at 43 (remarking that the class of 

pesticides encompasses such substances as cayenne pepper, chlordane, canola oil, 

baking soda, and wood preservatives). As Judge Wettick aptly observed, Dr. ZambelliWeiner herself recognized that “[p]esticides represent a heterogenous[, or diverse,] 

group of formulated products that contain active ingredients and additives.” Walsh v. 

BASF Corp., No. GD-10-018588, slip op. at 19 n.17 (citing Deposition of April ZambelliWeiner, Ph.D., dated September 23, 2014, at 104-107) (emphasis in original). 

In other cases, and along with other Justices, I have recognized the difficulties 

facing plaintiffs in toxic tort cases involving exposure to multiple products and long 

latency periods. See, e.g., Gregg v. V-J Auto Parts, Inc., 596 Pa. 274, 291-92, 943 

A.2d 216, 226 (2007). Again, I would permit a fair degree of latitude, for example in 

terms of estimating exposure and dose. See, e.g., Rost, 637 Pa. at 676 n.13, 151 A.3d 

at 1063 n.13 (Saylor, C.J., dissenting). However, the proffer -- before a jury of 

laypersons --- of expert witnesses whose methodologies are replete with ungrounded 

extrapolations and other analytical gaps, large-scale abstractions, and patent circularity 
[J-92A-E-2019][M.O. – Donohue, J.] - 14

goes far beyond any reasonable conception of appropriate leeway. Accord Accutane, 

191 A.3d at 589 (emphasizing that the court’s function on review of novel scientific 

opinions “is to distinguish scientifically sound reasoning from that of the self-validating 

expert, who uses scientific terminology to present unsubstantiated personal beliefs”). 

For the above reasons, I would reverse the order of the Superior Court.

II. Response to the Concurring Opinion by Justice Wecht

According to Justice Wecht, the opinion that I authored in Betz suffers from a 

“reliance upon potentially misleading terminology” and “so muddied the waters that this 

Court should stabilize its characterization of the Frye standard[.]” Concurring Opinion, 

slip op. at 5. In this regard, he intimates that Betz “introduced into Pennsylvania law a 

‘conventionality’ requirement, suggesting that expert testimony in a scientific discipline 

is admissible only when the expert has ‘applied accepted scientific methodology in a 

conventional fashion in reaching his or her conclusions.’” Id. at 14 (emphasis in original; 

citation omitted). Justice Wecht further cites, inter alia, to Commonwealth v. Jacoby, 

642 Pa. 623, 170 A.3d 1065 (2017), as a decision evidencing the same deficiency 

which he attributes to Betz. See Concurring Opinion, slip op. at 14 & n.10.

As an initial matter, Justice Wecht’s opinion demonstrates a misunderstanding of 

the Betz decision, in that the “conventional fashion” language simply wasn’t used to 

redefine Frye’s general-acceptance standard. Rather, the phrase appears, in Betz, 

solely in a section entitled, “The Decision to Conduct a Frye Hearing.” Consistent with 

this heading, the passage discusses only the concept of the novelty of scientific 

evidence, which serves as the threshold to the entitlement to a Frye hearing. See Betz, 

615 Pa. at 544-46, 44 A.3d at 52-53 (“We conclude that a Frye hearing is warranted 

when a trial judge has articulable grounds to believe that an expert witness has not 
[J-92A-E-2019][M.O. – Donohue, J.] - 15

applied accepted scientific methodology in a conventional fashion in reaching his or her 

conclusions.” (emphasis added)).

Notably, this is the same limited context in which conventionality was considered 

in the Jacoby decision referenced by Justice Wecht. See Jacoby, 642 Pa. at 667, 170 

A.3d at 1091. Indeed, the novelty threshold was the only tier of a Frye analysis that the 

Jacoby Court was able to review, given that the trial court had denied the defendant’s 

motion for a Frye hearing, and accordingly, no application of the Frye generalacceptance test whatsoever had occurred in the case. See id. at 640, 170 A.3d at 

1075.7

Viewing the contested phraseology in its appropriate setting, I do not find it to be 

confusing, at all, to say that scientific methodology applied in an unconventional fashion 

fairly translates into novel scientific evidence (particularly since novelty and 

unconventionality are often used as synonyms). And the Court’s unanimous 

determination on this subject, in Betz, didn’t stray off course. Instead, the question of 

 

7 The “conventional fashion” language taken from Betz was also used in this manner in 

each of the remaining decisions and responsive opinions in this Court cited by the 

concurrence. See Mitchell v. Shikora, ___ Pa. ___, ___ n.12, 209 A.3d 307, 319 n.12 

(2019); Commonwealth v. Walker, 625 Pa. 450, 489, 92 A.3d 766, 790 (2014);

Commonwealth v. Treiber, 632 Pa. 449, 538, 121 A.3d 435, 488 (2015) (Saylor, C.J., 

dissenting).

Parenthetically, the majority opinion in Jacoby does manifest an idiosyncrasy in its own 

right, since it characterizes unconventionality in methodology as the exclusive measure 

for novelty. See Jacoby, 642 Pa. at 667, 170 A.3d at 1091. On the novelty issue, 

however, Betz only decided the issue that was before the Court -- i.e., whether the 

concept of novelty subsumed generally-accepted methodology applied in an 

unconventional fashion. There should never have been any doubt that Frye also 

extends to “novel science” -- for example, a new scientific test for truth-telling -- in the 

first instance. See Betz, 615 Pa. at 545, 44 A.3d at 53 (citing Grady, 576 Pa. at 557, 

839 A.2d at 1045).
[J-92A-E-2019][M.O. – Donohue, J.] - 16

whether the concept of novelty extended to novel (or unconventional) applications of 

otherwise-accepted scientific methodology was squarely presented by the litigants as a 

main, contested issue in the case.8 Furthermore, contrary to Justice Wecht’s 

characterization, the matter was decided on amply-developed reasoning.9

 

8

In this regard, the issue was raised and developed -- and discussed extensively -- by 

the parties and their amici. Compare Betz, 615 Pa. at 530-31, 44 A.3d at 43-44

(reflecting that the defendant-appellants contended that a Frye hearing was warranted 

because, while the challenged expert “ostensibly accepted the applicability of” 

conventional scientific methodology, his opinion “in substance, nevertheless disregards 

this elemental precept in its entirety”), with id. at 542-43, 44 A.3d at 51 (summarizing the 

plaintiff-appellees’ argument that there was “no justification for conducting a Frye

hearing,” since their expert’s methodology was “utterly mainstream”). 

9 Betz relates that Pennsylvania courts tend to downplay access to other rule-based 

tools for trial judges to screen scientific evidence, such as the ability to refuse to admit 

evidence to avoid unfair prejudice, confusion of the issues, or misleading the jury. See

Betz, 615 Pa. at 544, 44 A.3d at 52 (citing Pa.R.E. 403, as well as the helpfulness 

consideration of Rule of Evidence 702). This, of course, tends to elevate the 

importance of appropriate screening under Frye. Additionally, the Court reasoned as 

follows:

Various reasons underlie the preference to limit the courts' 

involvement in determining the admissibility of scientific 

evidence. There is the concern that liberality in allowing 

challenges would substantially increase the number of 

challenges (and cases in which lengthy pre-trial proceedings 

would ensue). The competency of trial judges to accept or 

reject scientific theories remains a legitimate subject of 

controversy. Additionally, a claim or defense in many cases 

may rise or fall based upon expert testimony and, therefore, 

there is some reluctance on the part of courts to deprive 

litigants of their day in court.

On the other hand, this Court has recognized the influential 

nature of expert testimony on complex subjects, and the 

potential that distortions have to mislead laypersons. See 

[Grady, 576 Pa.] at 558, 839 A.2d at 1045; Topa, 471 Pa. at 

231–33, 369 A.2d at 1281–82. It would be naïve, in this 

(continued...)
[J-92A-E-2019][M.O. – Donohue, J.] - 17

In any event, the digression about passages from Betz dedicated to novelty 

seems to me to be of little relevance to this case, since the claim that prevailed before 

Judge Wettick was that Dr. Brautbar’s methodology was not only unconventional, but it 

was wholly unscientific.10 One of the pillars of the Betz opinion is that trial judges are 

authorized -- and obliged upon proper challenge -- to screen against expert witnesses 

who profess to apply accepted scientific methodology but instead, present analyses 

suffering from material analytical gaps. See Betz, 615 Pa. at 553, 44 A.3d at 57-58. 

 

(...continued)

regard, to assume that the possibility for distortion is limited 

to the very newest realms of science. Cf. Grady, 576 Pa. at 

557, 839 A.2d at 1045 (explaining that Frye applies not only 

to novel science, but also where scientific methods are 

utilized in a novel way).

We therefore agree with Appellants that a reasonably broad 

meaning should be ascribed to the term “novel.” 

Betz, 615 Pa. at 545, 44 A.3d at 53.

10 In this regard, since unscientific methodology is also unconventional, there is a great 

deal of overlap between the terms. And I would submit that the greater range of cases 

in which scientific evidence is excluded, as this one, address evidence that is both 

unconventional and unscientific. See supra note 2. 

Certainly, the substantive Frye test shouldn’t be applied so stringently as to absolutely 

forbid scientific methodology applied in a unique way, so long as the new manner itself 

can reasonably be viewed as scientific (or as being sufficiently grounded in generallyaccepted principles). This is why the Betz Court chose the “unconventional” litmus 

solely to identify situations where the courts should take a close look (i.e., conduct a 

Frye hearing) to screen against unscientific lapses in the methodology, such as 

analytical gaps and abstractions.

As related above and below, the particular strain of “unconventionality” embedded in Dr. 

Brautbar’s opinions -- i.e. material analytical gaps and abstractions -- is and should be 

excluded from courtrooms. See infra.
[J-92A-E-2019][M.O. – Donohue, J.] - 18

The alternative to permitting trial courts to consider whether experts actually adhere to 

the methodology that they only facially espouse is to accept the sort of expert selfvalidation which is of great concern to most courts.11

 

One need look no further than the FBI’s recent revelation that, for decades, the 

government engendered the presentation of faulty forensic-science evidence -- in the 

form of microscopic hair analysis -- potentially impacting tens of thousands of criminal 

cases across the nation. See FBI Press Release, FBI Testimony on Microscopic Hair 

Analysis Contained Errors in at Least 90 Percent of Cases in Ongoing Review, at 2 

 

11 As a separate matter, during the course of his critique of Betz, without citation, Justice 

Wecht restates the holding as follows: 

In Betz, . . . the Court appeared to hold, and unquestionably 

implied, that when an expert testifies that any exposure to a 

toxic substance enhances the risk that the exposed party will 

suffer injury as a consequence of that particular exposure, 

the expert inadmissibly suggests that the exposure in 

question, even when de minimis, is a substantial cause of 

the injury.

Concurring Opinion, slip op. at 20. In Betz, however, there simply was no reason for the 

Court to infer anything about substantial-factor causation from discussions by the 

challenged expert about increased risk in the abstract. Rather, the case concerned the 

challenged expert’s explicit opinion that was offered as the sole evidence to address the 

plaintiff-appellees’ burden to prove substantial-factor causation. In this regard, the 

specific opinion at issue was that de minimus exposure -- i.e., breathing a single 

asbestos fiber from a defendant’s product -- was a substantial factor in causing any 

given instance of asbestos-related disease in any individual who was so exposed. See 

Betz, 615 Pa. at 510, 44 A.3d at 31. 

Along these lines, I find the concurrence’s assertion that Rost appropriately overruled 

the above rationale attributed to Betz to be equally misplaced. See Concurring Opinion, 

slip op. at 20-21.

I have acknowledged nonetheless, that the majority decision in Rost did work a distinct 

retrenchment relative to Betz, at least insofar as concerns asbestos-mesothelioma 

cases. See supra note 2.
[J-92A-E-2019][M.O. – Donohue, J.] - 19

(Apr. 2, 2015). Of course, the misuse of science in courtrooms tends to impugn the 

integrity of the judicial system. See, e.g., Commonwealth v. Chmiel, 643 Pa. 216, 225, 

173 A.3d 617, 622 (2017) (referencing a Washington Post article charging that the FBI’s 

review was “a watershed in one of the country’s largest forensic scandals, highlighting 

the failure of the nation’s courts for decades to keep bogus scientific information from 

juries” (emphasis added)). See generally Edward J. Imwinkelreid, The Best Insurance 

Against Miscarriages of Justice Caused By Junk Science: An Admissibility Test That Is 

Scientifically and Legally Sound, 81 ALB. L. REV. 851, 851 (2018) (“Inaccurate expert 

testimony is a ‘recurrent theme[]’ in wrongful conviction studies.”). 

Accordingly, courts that look beyond mere acceptance of an expert’s own 

personal claim to adherence to an accepted scientific methodology quite appropriately 

seek to protect the integrity of the judicial process. 

Notably, other jurisdictions adhering to Frye’s general-acceptance litmus have 

approved judicial screening against the admission of faulty expert analyses in a fashion 

very similar to that required under Betz. See, e.g., Goeb v. Tharaldson, 615 N.W.2d 

800, 816 (Minn. 2000) (applying a Frye analysis to require a proponent of scientific 

evidence to show that the “methodology used [by the expert] is reliable and in the 

particular instance produced reliable results,” and affirming the exclusion of testimony 

from an expert whose analysis made “too great a leap” from the data gathered 

(emphasis added)). See generally Blackwell v. Wyeth, 971 A.2d 235, 254 (Md. 2009) 

(“The ‘analytical gap’ concept also has been employed by some of our sister states in a 

Frye analysis.” (citing, inter alia, the Minnesota Supreme Court’s decision in Goeb)).12

 

12 Maryland maintains a variant of the Frye test which distinguishes between generally 

accepted methodology and generally accepted analysis, while clarifying that both are 

required “to avoid the pitfalls of an ‘analytical gap.’” Blackwell, 971 A.2d at 255. In my 

view, it is largely a semantic issue whether an expert who professes to have applied a 

(continued...)
[J-92A-E-2019][M.O. – Donohue, J.] - 20

Nor was Betz’s review of a scientist’s actual methodology a novelty in 

Pennsylvania. In Blum v. Merrell Dow Pharmaceuticals, Inc., the challenged expert 

testified at a Frye hearing that his opinions “were based on generally accepted 

methods.” Blum by Blum v. Merrell Dow Pharmaceuticals, Inc., 705 A.2d 1314, 1321 

(Pa. Super. 1997), aff’d, 564 Pa. 3, 764 A.2d 1 (2000). Nevertheless, the Superior 

Court concluded that such self-validating testimony was “not enough” to carry the 

proponent’s burden at a Frye hearing. Id. Significantly, in affirming this conclusion, this 

Court reviewed the record and explained that the expert “engaged in a selective review 

of the data from several” studies; “detached the underlying data from the controls set up 

by the studies”; and “worked backwards through the science, from the statistical results 

back to the studies in the first place.” Blum, 564 Pa. at 7 n.5, 764 A.2d at 4 n.5. As 

such, and as in Betz, the Court concluded that “[t]his procedure cannot be fairly 

described as generally accepted methodology for purposes of the Frye standard.” Id.

As I have previously explained, I don’t believe the present case presents an 

appropriate vehicle for engaging in a merits defense of either the Frye or Daubert

criteria or any other existing or proposed standard, since there is no present advocacy 

on the subject. I observe, however, that some of the authorities that Justice Wecht 

 

(...continued)

generally accepted scientific methodology -- but who has in fact failed to do so -- hasn’t 

applied that methodology as a factual matter, or has been deficient in his applied 

reasoning. Under either understanding, the expert’s unscientific and misleading 

testimony presents precisely the same danger associated with its misuse in a 

courtroom.

In this regard, a constant and contested theme, in this line of cases, is that one party’s 

expert will say that he or she followed generally-accepted scientific methodology, and 

the adversary’s expert will say this is not so. There would be no reason for a Frye

hearing if a neutral judicial official were not interposed to resolve such a material factual 

dispute.
[J-92A-E-2019][M.O. – Donohue, J.] - 21

discusses in his defense of Frye depart greatly from his central thesis. For example, the 

concurrence references an article by law fellow and Ph.D. candidate James R. Dillon to 

support the propositions that judges lack the expertise to address scientific evidence in 

the courtroom, and that Frye more appropriately delegates the question of the reliability 

of the actual methodology or reasoning employed to experts selected by the litigants. 

See Concurring Opinion at 19 (citing James R. Dillon, Expertise on Trial, 19 COLUM. SCI.

& TECH. L. REV. 247, 260, 272 (2018)).

Relative to the comment about judicial expertise, however, the article also 

espouses the view that jurors lack the necessary competence to assess the reliability of 

scientific evidence. See, e.g., Dillon, Expertise on Trial, 19 COLUM. SCI. & TECH. L. REV.

at 278 (opining that “[j]urors often fail to understand and apply scientific testimony 

correctly, even when the underlying science itself is relatively clear,” and that jurors tend 

to rely on “cognitive shortcuts,” such as a focus upon “perceived expertise”). Moreover, 

the theme runs throughout the Dillon article that judges must implement an effective 

gatekeeping function to keep faulty science out of courtrooms, at the risk of 

compromising the integrity of the judicial system. In this regard, the author departs 

roundly from Justice Wecht’s position concerning the effectiveness of traditional 

adversarial tools of common-law adjudication, including cross-examination, the 

introduction of competing evidence, and argumentation by counsel. Compare

Concurring Opinion, slip op. at 8, with Dillon, Expertise on Trial, 19 COLUM. SCI. & TECH.

L. REV. at 280 (“The empirical literature also casts doubt on the effectiveness of the 

traditional tools of the adversarial model . . . in mitigating jurors’ cognitive fallibilities.”). 

The author further submits that the Frye approach, devised in 1923, had failed to 

counteract a “sporting theory” associated with the use of partisan expert witnesses in 

courtrooms, which was appalling to the public and produced a crisis of confidence in the 
[J-92A-E-2019][M.O. – Donohue, J.] - 22

judicial system, at least until courts began to “apply Frye more stringently in the 1970s.” 

Id. at 259. Ultimately, the author proposes the appointment of a “scientific adjunct with 

expertise in each relevant scientific domain,” in every civil and criminal case, who would 

have the authority to engage in sua sponte gatekeeping; to conduct and implement 

independent research and analyses, respectively; and to overturn jury verdicts which 

the adjunct finds to be contrary to scientific fact. Id. at 297-300. 

Plainly, this article does not comport with Justice Wecht’s position that 

Pennsylvania should remain “a Frye stalwart” with no further consideration of any other 

alternative. Compare Concurring Opinion, slip op. at 13, with Dillon, Expertise on Trial, 

19 COLUM. SCI. & TECH. L. REV. at 312 (“Maintaining the status quo is not a viable 

option.”).

Personally, at this point in time, I wouldn’t endorse the Dillon article any more 

than I would subscribe to Justice Wecht’s sua sponte defense of Frye.

13

 Instead, I 

reiterate my belief that very serious and difficult questions remain that would be better 

addressed by this Court upon developed argumentation and with due consideration of 

the many concerns arising out of the ongoing experience with the misuse of faulty 

science in courtrooms.14

 

13 I note that there are other proposals for improvement that may also merit serious 

consideration. See, e.g., Imwinkelreid, The Best Insurance Against Miscarriages of 

Justice Caused By Junk Science: An Admissibility Test That Is Scientifically and 

Legally Sound, 81 ALB. L. REV. at 865-66.

14 Notably, as well, the Betz Court never made a definitive ruling as to whether trial 

courts could separately enforce Rule of Evidence 702’s requirement that expert opinion 

must assist the trier of fact to understand the evidence or determine a fact in issue, or 

Rule 403’s screening requirement against unfair prejudice, confusion of the issues, or 

misleading of the jury. See Pa.R.E. 403, 702. From my point of view, close 

consideration also should be accorded to empowering trial courts to separately enforce 

these material requirements in the expert-testimony arena. But see Majority Opinion, 

slip op. at 21 n.7 (“To the extent that Pennsylvania trial courts conduct an ‘essential 

(continued...)
[J-92A-E-2019][M.O. – Donohue, J.] - 23

Justice Todd joins this dissenting opinion.

 

(...continued)

review for reliability,’ that review may consist only of establishing that the expert utilized 

generally accepted methodologies in reaching his or her scientific conclusions.” (internal 

citation omitted)).