Amicus Curiae Brief — Union Carbide Corporation, et al., Petitioners v. Lee Ann Sommerville

No. 25-919

In the

Supreme Court of the United States

—————♦—————

UNION CARBIDE CORPORATION, ET AL.,

Petitioners,

v.

LEE ANN SOMMERVILLE,

Respondent.

—————♦—————

On Petition for Writ of Certiorari to the United

States Court of Appeals for the Fourth Circuit

—————♦—————

BRIEF OF THE CHAMBER OF COMMERCE OF

THE UNITED STATES OF AMERICA,

AMERICAN TORT REFORM ASSOCIATION,

AMERICAN CHEMISTRY COUNCIL, NATIONAL

ASSOCIATION OF MANUFACTURERS,

AMERICAN FUEL & PETROCHEMICAL

MANUFACTURERS, CROPLIFE AMERICA,

PHARMACEUTICAL RESEARCH AND

MANUFACTURERS OF AMERICA, AMERICAN

PETROLEUM INSTITUTE, ADVANCED

MEDICAL TECHNOLOGY ASSOCIATION, AND

BUSINESS ROUNDTABLE AS AMICI CURIAE IN

SUPPORT OF PETITIONERS

—————♦—————

JONATHAN D. URICK

KEVIN R. PALMER

U.S. CHAMBER OF

COMMERCE LITIGATION

CENTER

1615 H Street NW

Washington, DC 20062

MATTHEW P. HOOKER

Counsel of Record

WILLIAM W. METCALF

ALSTON & BIRD LLP

1120 S. Tryon St.

Suite 300

Charlotte, NC 28203

(704) 444-1000

matthew.hooker@alston.com

Counsel for Amici Curiae

[Additional counsel listed on inside cover]

H. SHERMAN JOYCE

LAUREN SHEETS JARRELL

AMERICAN TORT REFORM

ASSOCIATION

1101 Connecticut

Ave. NW

Suite 400

Washington, DC 20036

SONJA RODMAN

AMERICAN CHEMISTRY

COUNCIL

655 New York Ave. NW

Washington, DC 20001

ERICA KLENICKI

CAROLINE MCAULIFFE

NATIONAL ASSOCIATION

OF MANUFACTURERS

733 10th Street NW

Suite 700

Washington, D.C. 20001

MICHAELANGELO FURNARI

AMERICAN FUEL &

PETROCHEMICAL

MANUFACTURERS

1800 M Street NW

Suite 900N

Washington, DC 20036

RACHEL G. LATTIMORE

EDWARD C. THOMAS

CROPLIFE AMERICA

4201 Wilson Blvd.

Suite 700

Arlington, VA 22203

JAMES C. STANSEL

MELISSA B. KIMMEL

PHARMACEUTICAL

RESEARCH AND

MANUFACTURERS OF

AMERICA

670 Maine Ave. SW

Suite 1000

Washington, D.C. 20024

MEREDITH B. CODY

RYAN MEYERS

JOHN WAGNER

AMERICAN PETROLEUM

INSTITUTE

200 Massachusetts

Ave. NW

Washington, DC 20001

PAT FOGARTY

ADVAMED -- ADVANCED

MEDICAL TECHNOLOGY

ASSOCIATION

1301 Pennsylvania

Ave. NW

Suite 400

Washington, DC 20004

LIZ DOUGHERTY

BUSINESS ROUNDTABLE

1000 Maine Ave. SW

Washington, DC 20024

Counsel for Amici Curiae

i

TABLE OF CONTENTS

Page

INTEREST OF AMICI CURIAE ................................ 1

INTRODUCTION AND SUMMARY OF

ARGUMENT ............................................................... 5

ARGUMENT ............................................................. 11

I.

RULE 702’S GATEKEEPING FUNCTION IS

GROUNDED IN THE NEED TO PROTECT

JURIES FROM UNRELIABLE EVIDENCE... 11

II.

THE DECISION BELOW REPUDIATES

DISTRICT COURTS’ GATEKEEPING ROLE

IN CONTRAVENTION OF THIS COURT’S

AND THE ADVISORY COMMITTEE’S

CLEAR INSTRUCTION. .................................. 14

III. ONGOING WEAKENING OF DISTRICT

COURTS’ GATEKEEPING ROLE HARMS

LITIGANTS AND THE JUDICIAL SYSTEM. 19

CONCLUSION .......................................................... 24

ii

TABLE OF AUTHORITIES

Page(s)

Cases

Alford v. NFL Player Disability

& Survivor Benefit Plan,

2025 WL 3274428 (D. Md. Nov. 24, 2025) ............23

Bourjaily v. United States,

483 U.S. 171 (1987) ..................................................6

Bresler v. Wilmington Trust,

855 F.3d 178 (4th Cir. 2017) .........6-8, 14, 15, 19, 23

Daubert v. Merrell Dow Pharms., Inc.,

509 U.S. 579 (1993) ............. 5-7, 9, 11-13, 14, 20-22

Dodge v. Cotter Corp.,

328 F.3d 1212 (10th Cir. 2012) ................................9

Doucette v. Jacobs,

106 F.4th 156 (1st Cir. 2024) ...................................8

EcoFactor v. Google,

137 F.4th 1333 (Fed. Cir. 2025).........................9, 18

Engilis v. Monsanto Co.,

151 F.4th 1040 (9th Cir. 2025) ..........................9, 18

Gen. Elec. Co. v. Joiner,

522 U.S. 136 (1997) ...................................... 6, 14, 21

Hutto v. Davis,

454 U.S. 370 (1982) ................................................10

In re Camp Lejeune Water Litig.,

2025 WL 3565850 (E.D.N.C. Dec. 12, 2025) .........22

In re Onglyza (Saxagliptin) & Kombiglyze

(Saxagliptin & Metformin) Prods. Liab. Litig.,

93 F.4th 339 (6th Cir. 2024) ..............................9, 18

iii

Kumho Tire Co. v. Carmichael,

526 U.S. 137 (1999) .......................... 6, 10, 11, 13, 22

Michael’s Fabrics, LLC v. Donegal Mut. Ins. Co.,

2025 WL 2624280 (D. Md. Sep. 11, 2025) ................23

Milward v. Acuity Specialty Products Group, Inc.,

639 F.3d 11 (1st Cir. 2011) ....................................19

Mincey v. Se. Farm Equip.,

2025 WL 2450913 (D.S.C. Aug. 26, 2025) .............23

Nairne v. Landry,

151 F.4th 666 (5th Cir. 2025) ............................9, 18

R&J Components Corp. v. Centimark Corp.,

2025 WL 3732157 (D.S.C. Nov. 18, 2025) .............23

Rodríguez v. Hosp. San Cristobal,

91 F.4th 59 (1st Cir. 2024) .................................8, 19

Sprafka v. Medical Device Bus. Servs.,

139 F.4th 656 (8th Cir. 2025) ............................9, 18

United States v. Frazier,

387 F.3d 1244 (11th Cir. 2004) ................................9

Williams v. BP Expl. & Prod., Inc.,

143 F.4th 593 (5th Cir. 2025) ............................9, 18

Statutes and Other Authorities

28 U.S.C. § 2072(a)–(b) .............................................19

Fed. R. Evid. 104 .......................................................11

Fed. R. Evid. 104(a)............................... 6, 7, 11, 15, 17

Fed. R. Evid. 702 ............................................. 5-22, 24

Fed. R. Evid. 702(b)............................... 5, 6, 14, 16, 18

Fed. R. Evid. 702(c) .....................................................5

Fed. R. Evid. 702(d)...............................................5, 16

iv

Fed. R. Evid. 702 advisory committee’s notes to

2000 amendments ..............................................6, 11

Fed. R. Evid. 702 advisory committee’s notes to

2023 amendments .........................6, 7, 13, 15-17, 18

Supreme Court Rule 37.2 ...........................................1

Supreme Court Rule 37.6 ...........................................1

Margaret A. Berger, The Admissibility of Expert

Testimony, in Fed. Jud. Ctr., Reference Manual

on Scientific Evidence 11 (3d ed. 2011) .................20

Stephen Breyer, Introduction, in Fed. Jud. Ctr.,

Reference Manual on Scientific Evidence 1 (3d

ed. 2011) .................................................................21

H.R. Doc. No. 118-33 (2023), available at

https://tinyurl.com/vjhtk46x ..............................7, 16

Learned Hand, Historical and Practical

Considerations Regarding Expert Testimony,

15 Harv. L. Rev. 40 (1901) .....................................10

Peter Huber, Junk Science and the Jury, 1990 U.

Chi. Legal F. 273 (1990) ........................................22

Lawyers for Civil Justice, Comment to the

Advisory Committee on Evidence Rules (Sep. 1,

2021), https://tinyurl.com/mutwkrmv ...................15

Memorandum from Daniel J. Capra, Reporter,

Advisory Committee on Evidence Rules, to

Advisory Committee on Evidence Rules,

Possible Amendment to Rule 702 (Apr. 1, 2021),

in Advisory Committee on Evidence Rules

Agenda

Book

(Apr.

30,

2021),

https://tinyurl.com/mw4u4wum ...................... 15-16

v

Memorandum from Patrick J. Schiltz, Chair,

Advisory Committee on Evidence Rules, to

John D. Bates, Chair, Standing Committee on

Rules of Practice and Procedure, Report of the

Advisory Committee on Evidence Rules (May

15, 2022), in Committee on Rules of Practice

and Procedure Agenda Book (June 7, 2022),

https://tinyurl.com/52edk2e2 .................................17

Ned Miltenberg, Out of the Fire and Into the

Fryeing Pan or Back to the Future, Trial, Mar.

2001 ........................................................................21

Christopher R.J. Pace, Admitting and Excluding

General Expert Testimony: The Eleventh

Circuit Construct, 37 Am. J. Trial Advoc. 47

(2013) ......................................................................21

Joseph M. Price & Gretchen Gates Kelly, Junk

Science in the Courtroom: Causes, Effects and

Controls, 19 Hamline L. Rev. 395 (1996) ..............22

Jed S. Rakoff, Science and the Law:

Uncomfortable Bedfellows, 38 Seton Hall L.

Rev. 1379 (2008)........................................... 9, 20, 21

Thomas D. Schroeder, Toward a More Apparent

Approach to Considering the Admission of

Expert Testimony, 95 Notre Dame L. Rev. 2039

(2020) ........................................................................7

Victor E. Schwartz & Cary Silverman, The

Draining of Daubert and the Recidivism of

Junk Science in Federal and State Courts, 35

Hofstra L. Rev 217 (2006) ................................21, 22

1

INTEREST OF AMICI CURIAE 1

The Chamber of Commerce of the United States of

America is the world’s largest business federation. It

represents approximately 300,000 direct members

and indirectly represents the interests of more than

three

million

companies

and

professional

organizations of every size, in every industry sector,

and from every region of the country. An important

function of the Chamber is to represent the interests

of its members in matters before Congress, the

Executive Branch, and the courts. To that end, the

Chamber regularly files amicus curiae briefs in cases,

like this one, that raise issues of concern to the

nation’s business community.

The American Tort Reform Association (ATRA) is

a national, nonpartisan, nonprofit coalition of large

and small businesses, trade associations, and

professional firms. ATRA is dedicated to improving

the civil justice system with a focus on promoting

fairness, balance, efficiency, and predictability in civil

litigation. In addition to legislative efforts and public

education outreach, one of ATRA’s important

functions is to file amicus curiae briefs in cases

involving important civil justice issues.

The American Chemistry Council (ACC)

represents more than 190 of the leading companies

1 In accordance with Rule 37.6, amici curiae state that no

counsel for any party authored this brief in whole or in part, and

no entity or person, aside from amici curiae, their members, or

their counsel, made any monetary contribution intended to fund

the preparation or submission of this brief. Counsel of record

received timely notice of amici’s intent to file this brief under

this Court’s Rule 37.2.

2

engaged in the business of chemistry—an innovative

economic growth engine that is helping to solve the

biggest challenges facing our country and the world.

Its members are companies of all sizes. In the United

States, the business of chemistry generates $673

billion annually, and employs 547,000 Americans

with average wages of over $100,000 annually. The

business supports another 3.2 million jobs and 25% of

the U.S. GDP. ACC’s members are the people and

companies creating the groundbreaking products

that improve the world all around us by making it

healthier, safer, more sustainable and more

productive. From consumer products like lotions and

deodorants to safety equipment like helmets and

eyewear, chemistry plays an essential role in products

and technologies used by people every day. The

American Chemistry Council’s mission is to advocate

for the people, policy, and products of chemistry that

make the United States the global leader in

innovation and manufacturing. It supports common

sense and science-based approaches to major public

policy issues.

The National Association of Manufacturers (NAM)

is the largest manufacturing association in the United

States, representing small and large manufacturers

in all fifty states and in every industrial sector.

Manufacturing employs nearly 13 million people,

contributes $2.9 trillion to the economy annually, has

the largest economic impact of any major sector, and

accounts for over half of all private-sector research

and development in the nation, fostering the

innovation that is vital for this economic ecosystem to

thrive. The NAM is the voice of the manufacturing

community and leading advocate for a policy agenda

3

that helps manufacturers compete in the global

economy and create jobs across the United States.

American Fuel & Petrochemical Manufacturers

(AFPM) is a national trade association representing

nearly all U.S. refining and petrochemical

manufacturing capacity. AFPM members support

more than three million quality jobs, contribute to our

economic and national security, and enable the

production of thousands of vital products used by

families and businesses throughout the U.S.

CropLife America is the national trade association

for the pesticide industry, representing developers,

manufacturers, formulators, and distributors of

pesticides for agriculture and pest management

solutions. CropLife America’s members—ranging

from small companies to large corporations—produce,

sell, and distribute virtually all pesticide products

used by American farmers. Member companies have

invested billions of dollars in research and testing of

their pesticide products to help ensure their safety

when used as directed on the federally required label.

The Pharmaceutical Research and Manufacturers

of America (PhRMA) represents the country’s leading

innovative biopharmaceutical research companies,

which are focused on developing innovative medicines

that transform lives and create a healthier world.

Together, PhRMA’s members are fighting for

solutions to ensure patients can access and afford

medicines that prevent, treat, and cure disease.

PhRMA member companies have invested more than

$850 billion in the search for new treatments and

cures over the last decade, supporting nearly five

million jobs in the United States.

4

The American Petroleum Institute (API)

represents all segments of America’s natural gas and

oil industry, which supports nearly 11 million U.S.

jobs and is backed by a growing grassroots movement

of millions of Americans. API’s approximately 600

members produce, process and distribute the majority

of the nation’s energy. API was formed in 1919 as a

standards-setting organization and has developed

more than 800 standards to enhance operational and

environmental safety, efficiency and sustainability.

The Advanced Medical Technology Association

(AdvaMed) is the world’s largest medical-technology

association representing device, diagnostics, imaging,

and digital technology manufacturers that are

transforming healthcare through earlier disease

detection, less-invasive medical procedures, and

more-effective treatments. Its 650-plus member

companies span every field of medical science, and

range from cutting-edge startups to multinational

manufacturers. AdvaMed’s members are dedicated to

advancing clinician and patient access to safe,

effective medical technologies. AdvaMed has

participated as amicus curiae in numerous cases

involving the admissibility of expert testimony,

scientific reliability, and the proper enforcement of

Rule 702 because these issues directly affect the

medical technology ecosystem and the patients it

serves. A legal regime that tolerates unreliable expert

opinions threatens not only due process for

defendants, but also the innovation pipeline that

produces safer, more effective medical care.

Business Roundtable represents more than 200

chief executive officers of America’s leading

companies. Business Roundtable CEOs lead U.S.-

5

based companies that support one in four American

jobs and almost a quarter of U.S. gross domestic

product. Business Roundtable was founded on the

belief that businesses should play an active and

effective role in the formulation of public policy, and

Business Roundtable members develop and advocate

for policies to promote a thriving U.S. economy and

expanded opportunity for all. Business Roundtable

participates in litigation as amicus curiae when

important business interests are at stake.

INTRODUCTION AND

SUMMARY OF ARGUMENT

Under Federal Rule of Evidence 702, “[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 the proponent

demonstrates to the court that it is more likely than

not that,” among other things, the expert’s testimony

(1) is “based on sufficient facts or data,” (2) is “the

product of reliable principles and methods,” and

(3) “reflects a reliable application of the principles and

methods to the facts of the case.” Fed. R. Evid.

702(b)–(d) (emphasis added). The “overarching

subject” of Rule 702’s requirements “is the scientific

validity—and thus the evidentiary relevance and

reliability—of the principles that underlie” the

proposed expert testimony. Daubert v. Merrell Dow

Pharms., Inc., 509 U.S. 579, 594–95 (1993).

In Daubert, this Court explained that the task of

evaluating the reliability of expert testimony—as

Rule 702 requires—falls within the province of the

district judge. Id. at 597 (“Rule 702 . . . assign[s] to

the trial judge the task of ensuring that an expert’s

6

testimony both rests on a reliable foundation and is

relevant to the task at hand.”). In doing so, the Court

recognized that Rule 702 requires district judges to

perform a “gatekeeping” function to “ensure that any

and all scientific testimony or evidence admitted is

not only relevant, but reliable.” Id. at 589, 597.

Following Daubert, this Court has repeatedly

confirmed that a district court’s responsibility to

shield juries from unreliable expert testimony

includes refusing to admit it in the first instance.

Kumho Tire Co. v. Carmichael, 526 U.S. 137, 141–42

(1999); Gen. Elec. Co. v. Joiner, 522 U.S. 136, 142

(1997).

Even so, “many courts have held that the critical

questions of the sufficiency of an expert’s basis, and

the application of the expert’s methodology, are

questions of weight” to be resolved by juries—“not

[questions of] admissibility” to be resolved by the

district court. Fed. R. Evid. 702 advisory committee’s

notes to 2023 amendments. Among those errant

decisions is the Fourth Circuit’s in Bresler v.

Wilmington Trust, 855 F.3d 178 (4th Cir. 2017).

There, the Fourth Circuit held that “questions

regarding the factual underpinnings of [an] expert

witness’ opinion affect the weight and credibility of

the witness’ assessment, not its admissibility.” Id. at

195 (cleaned up). That holding “effectively vitiated

the application of Rule 104(a) to Rule 702(b)” 2 and

2 Under Federal Rule of Evidence 104(a), “the proponent has

the burden of establishing that the pertinent admissibility

requirements are met by a preponderance of the evidence.” Fed.

R. Evid. 702 advisory committee’s notes to 2000 amendments

(citing Bourjaily v. United States, 483 U.S. 171 (1987)); see also

Fed. R. Evid. 104(a).

7

“[a]bdicat[ed] [courts’] charge under the Federal

Rules of Evidence and Daubert and its progeny to

make the hard call on admissibility.” Thomas D.

Schroeder, Toward a More Apparent Approach to

Considering the Admission of Expert Testimony, 95

Notre Dame L. Rev. 2039, 2043, 2049–50 (2020). 3

Bresler and decisions like it “are an incorrect

application of Rules 702 and 104(a).” Fed. R. Evid. 702

advisory committee’s notes to 2023 amendments.

That is why, in 2023, the Advisory Committee on

Evidence Rules amended Rule 702 to confirm that a

district court’s gatekeeping function includes the

obligation to determine whether the proponent of

expert testimony has demonstrated by a

preponderance of the evidence that the testimony is

sufficiently reliable to be considered by a jury. 4 The

Advisory Committee explained that the need to

“emphasiz[e] the preponderance standard in Rule 702

specifically was made necessary by the courts”—like

the Fourth Circuit in Bresler—“that have failed to

apply correctly the reliability requirements of that

rule.” Fed. R. Evid. 702 advisory committee’s notes to

2023 amendments. And it rejected the notion “that

arguments about the sufficiency of an expert’s basis

always go to weight and not admissibility.” Ibid.

3 Judge Schroeder chaired the Subcommittee of the Advisory

Committee on Evidence Rules that spearheaded the 2023

amendments to Rule 702.

4 See H.R. Doc. No. 118-33, at 18 (2023) (adding clause to

Rule 702 to clarify that an expert witness may testify “if the

proponent demonstrates to the court that it is more likely than

not that” Rule’s requirements are met), available at

https://tinyurl.com/vjhtk46x.

8

But in the decision below, the Fourth Circuit

eschewed the Advisory Committee’s guidance and

this Court’s clear direction and instead applied

Bresler’s outdated and incorrect approach to Rule 702.

The district court excluded an expert’s opinion on

ethylene oxide emissions from petitioners’ plant

because the expert had, among other things,

“commingled results from both” the at-issue plant and

another plant “not at issue in this case,” “treated data

from a single year as representative of . . . the entire

36-year period,” and used contradictory sets of

meteorological

data

from

non-representative

locations. Pet. at 7–9 (cleaned up). But the Fourth

Circuit faulted the district court for excluding the

expert’s opinion, holding that the exclusion was

inconsistent with Bresler’s mandate that juries, not

the district court, resolve “questions regarding the

factual underpinnings of the [expert] opinion” as a

matter of “weight and credibility of the witness’

assessment.” Pet.App.20a–27a (citing Bresler). In

doing so, the Fourth Circuit became the second circuit

(after the First Circuit) 5 to reaffirm incorrect “weight

not admissibility” jurisprudence in the wake of the

2023 amendments to Rule 702. Those two circuits

stand opposite the five circuits that have heeded the

2023 amendments and expressly confirmed that each

of Rule 702’s requirements must be satisfied by a

5 See also Rodríguez v. Hosp. San Cristobal, 91 F.4th 59, 70

(1st Cir. 2024) (“When the factual underpinning of an expert's

opinion is weak, it is a matter affecting the weight and credibility

of the testimony and thus a question to be resolved by the jury”

(cleaned up)); Doucette v. Jacobs, 106 F.4th 156, 169 (1st Cir.

2024).

9

preponderance of the evidence for expert testimony to

be admissible. 6

That trend is troubling. A district court’s

gatekeeping function under Daubert and Rule 702 is

critical to modern litigation. United States v. Frazier,

387 F.3d 1244, 1260 (11th Cir. 2004) (“The

importance of Daubert’s gatekeeping requirement

cannot be overstated.”); accord, e.g., Dodge v. Cotter

Corp., 328 F.3d 1212, 1226 (10th Cir. 2012) (noting

“the fundamental importance of properly performing

the gatekeeper function”). Advances in technology,

science, business, and other areas of society following

Rule 702’s adoption over fifty years ago have made

expert testimony more important as litigants seek to

marshal evidence in increasingly complex disputes.

Today’s litigants—and factfinders too—increasingly

turn to expert testimony to help prove and resolve

these matters. See Jed S. Rakoff, Science and the Law:

Uncomfortable Bedfellows, 38 Seton Hall L. Rev.

1379, 1379 (2008) (“[S]cience in all its forms . . . has

in recent years invaded the courtroom to an

unparalleled extent.”).

Accordingly, “expert evidence can be . . . powerful.”

Daubert, 509 U.S. at 595 (citation omitted). Yet at the

same time, it can also be “quite misleading because of

the difficulties in evaluating it.” Ibid. Indeed, an

6 Engilis v. Monsanto Co., 151 F.4th 1040, 1047–50 (9th Cir.

2025); In re Onglyza (Saxagliptin) & Kombiglyze (Saxagliptin &

Metformin) Prods. Liab. Litig., 93 F.4th 339, 348 n.7 (6th Cir.

2024); EcoFactor v. Google, 137 F.4th 1333, 1339 (Fed. Cir. 2025)

(en banc); Williams v. BP Expl. & Prod., Inc., 143 F.4th 593, 601

(5th Cir. 2025); Nairne v. Landry, 151 F.4th 666, 697–98 (5th

Cir. 2025); Sprafka v. Medical Device Bus. Servs., 139 F.4th 656,

660–61 (8th Cir. 2025).

10

“expert’s testimony often will rest ‘upon an experience

confessedly foreign in kind to [the jury’s] own.’”

Kumho Tire, 526 U.S. at 149 (quoting Learned Hand,

Historical and Practical Considerations Regarding

Expert Testimony, 15 Harv. L. Rev. 40, 54 (1901)).

When a district court shirks its gatekeeping

duties—or, as in the case below, is prohibited

altogether from exercising them—it risks admitting

unreliable evidence that may mislead and even sway

the jury.

That poses problems for litigants—particularly

defendants. Without assurance that only expert

testimony that satisfies Rule 702’s threshold

reliability requirements will be admitted, defendants

may be forced to proceed to trial and risk being

subjected to liability based on plainly unreliable

expert testimony. Defendants may also face prolonged

litigation and higher litigation costs if unreliable

expert testimony revives a plaintiff’s otherwise weak

or speculative claims. And on top of that, the Fourth

Circuit’s exacerbation of the split between federal

circuits regarding the proper application of Rule 702,

as amended in 2023, invites inconsistent verdicts and

forum shopping, undermines the weight of the

Advisory Committee’s guidance, and delegitimizes

the Rules of Evidence themselves. Together, this

reduces confidence in our judicial system and can call

its fairness into question.

This Court’s review is necessary to resolve the

circuit split. Although some courts may be unwilling

to heed the Advisory Committee’s guidance, they are

bound to accept this Court’s rulings. See Hutto v.

Davis, 454 U.S. 370, 375 (1982) (“[U]nless we wish

anarchy to prevail within the federal judicial system,

11

a precedent of this Court must be followed by the

lower federal courts no matter how misguided the

judges of those courts may think it to be.”). And if the

Fourth Circuit’s decision is any indication, some

courts will refuse to reverse course even following the

2023 amendments until this Court intercedes. This

Court can and should take this opportunity to confirm

the district courts’ duty to gatekeep expert testimony

admitted for juries’ consideration by carefully

applying Rule 702’s reliability requirements and the

burden of proof to show their satisfaction.

ARGUMENT

I.

RULE 702’S GATEKEEPING FUNCTION

IS GROUNDED IN THE NEED TO

PROTECT JURIES FROM UNRELIABLE

EVIDENCE.

Rule 702 charges district courts with

“gatekeeping” any expert testimony admitted into

evidence. See Daubert, 509 U.S. at 597; Kumho Tire,

526 U.S. at 141; Fed. R. Evid. 702 advisory

committee’s notes to 2000 amendments. The Rule’s

delegation of the gatekeeping function to the district

court as a threshold matter is confirmed by Federal

Rule of Evidence 104, which provides that “[t]he court

must decide any preliminary question about whether

a witness is qualified, a privilege exists, or evidence is

admissible.” Fed. R. Evid. 104(a). District courts

discharge their gatekeeping duties by admitting

expert testimony only if the proponent can show, by a

preponderance of the evidence, that the testimony

meets four requirements: (1) it is helpful to the trier

of fact, (2) it has a sufficient factual basis, (3) it is

based on reliable principles and methods, and (4) it

12

reflects a reliable application of the methodology to

the facts of the case. Fed. R. Evid. 702. It is only after

the district court makes such a finding that any

remaining disputes go to the jury for resolution as

issues of weight. Thus, when a dispute regarding the

facts, principles, or methods underlying an expert’s

testimony bears on whether Rule 702’s requirements

are satisfied in the first instance, those disputes are

questions of admissibility.

Rule 702’s gatekeeping function serves to “ensure

that any and all scientific testimony or evidence

admitted is not only relevant, but reliable.” Daubert,

509 U.S. at 589. It reflects a balancing of the value of

helpful expert testimony against the danger of

unreliable and misleading expert testimony. For

litigants to realize the benefit of that balance, courts

must carefully leverage their legal expertise to apply

Rule 702’s substantive requirements and the burden

of proof that the Rule imposes on the proponent of the

testimony offered. That exercise does not require

district courts to ensure that expert testimony is

unassailable as a scientific or evidentiary matter

before admitting the testimony into evidence—it

merely requires them to ensure that the testimony is

based on sufficiently reliable facts and methods, such

that the jury’s conclusion about the testimony’s

weight (whatever it may be) can be trusted.

District courts’ obligation to evaluate expert

testimony and screen out that which is irrelevant or

unreliable is a matter of critical significance to the

proper functioning of the federal judicial system. And

this obligation cannot be passed along to jurors:

13

Judicial gatekeeping is essential

because . . . jurors may be unable, due

to lack of specialized knowledge, to

evaluate meaningfully the reliability of

scientific

and

other

methods

underlying expert opinion, [and] may

also lack the specialized knowledge to

determine whether the conclusions of

an expert go beyond what the expert’s

basis and methodology may reliably

support.

Fed. R. Evid. 702 advisory committee’s notes to 2023

amendments; see also Kumho Tire, 526 U.S. at 149

(an “expert’s testimony often will rest upon an

experience confessedly foreign in kind to [the jury’s]

own” (cleaned up)). It is thus plainly wrong for a

district judge to mischaracterize potential flaws of an

expert’s methodology as merely matters of

evidentiary weight exclusively for the jury to assess.

Indeed, as this Court has acknowledged, “[e]xpert

evidence can be both powerful and quite misleading

because of the difficulty in evaluating it.” Daubert,

509 U.S. at 595 (citation omitted). Without district

courts’ gatekeeping unreliable expert testimony,

juries—and the verdicts they reach—are susceptible

to influence by “expertise that is fausse and science

that is junky.” Kumho Tire, 526 U.S. at 158–59

(Scalia, J., concurring). On the other hand, when

district courts faithfully carry out their gatekeeper

function, they enable juries to resolve cases “finally

and quickly,” free from reliance on expert testimony

“that [is] probably wrong.” Daubert, 509 U.S. at 597.

Such testimony is “of little use . . . in the project of

reaching a quick, final, and binding legal judgment—

14

often of great consequence—about a particular set of

events in the past.” Ibid.

II.

THE DECISION BELOW REPUDIATES

DISTRICT

COURTS’

GATEKEEPING

ROLE IN CONTRAVENTION OF THIS

COURT’S

AND

THE

ADVISORY

COMMITTEE’S CLEAR INSTRUCTION.

In the decision below, the Fourth Circuit reversed

the district court’s exclusion of an expert’s testimony

regarding ethylene oxide emissions. The district court

issued a reasoned opinion determining that the data

inputs and methodology used by the expert to model

the emissions were fundamentally flawed and

unreliable. The Fourth Circuit disagreed, finding that

the district court “violated Bresler’s holding that

‘questions regarding the factual underpinnings of the

[expert witness’] opinion affect the weight and

credibility of the witness’ assessment, not its

admissibility.’” Pet.App.20a–22a; see also id. at

24a–25a (“The district court again conflated

admissibility with the weight a factfinder might

attribute [the expert’s] testimony based on his choice

of data.”). But the notion that “district courts may not

decide that an expert’s opinion lacks sufficient

support in the record . . . or conclude ‘that there is

simply too great an analytical gap between [an

expert’s data] and the opinion proffered’” conflicts

with Rule 702 and this Court’s jurisprudence. Id. at

36a (Diaz, C.J., dissenting) (citing Fed. R. Evid. 702(b)

and quoting Gen. Elec. Co., 522 U.S. at 146).

The Fourth Circuit’s decision also flouts the 2023

amendments to Rule 702. When the Advisory

Committee on Evidence Rules began the proceedings

15

leading to the 2023 amendments, it set out to correct

decisions like Bresler that stubbornly adhered to the

notion that questions about the reliability of expert

testimony always go only to the weight of the

testimony—and thus, should be resolved by the jury.

Fed. R. Evid. 702 advisory committee’s notes to 2023

amendments (“[M]any courts have held that the

critical questions of the sufficiency of an expert’s

basis, and the application of the expert’s methodology,

are questions of weight and not admissibility. These

rulings are an incorrect application of Rules 702 and

104(a).”). Indeed, in its comment to the Advisory

Committee regarding the Rule 702 amendments,

Lawyers for Civil Justice identified hundreds of

courts of appeals decisions between 2015 and 2021

suggesting (incorrectly) that questions regarding the

factual bases or foundations of expert opinions go to

the weight of the experts’ opinions and are, therefore,

merely for cross-examination and jury resolution. 7

The Advisory Committee’s reporter explained the

same in the Committee’s official agenda book: “Many

opinions can be found with broad statements such as

‘challenges to the sufficiency of an expert’s basis raise

questions of weight and not admissibility’—a

misstatement made by circuit courts and district

courts in a disturbing number of cases.” 8

7 See Lawyers for Civil Justice, Comment to the Advisory

Committee on Evidence Rules

https://tinyurl.com/mutwkrmv.

at

2

(Sep.

1,

2021),

8 Memorandum from Daniel J. Capra, Reporter, Advisory

Committee on Evidence Rules, to Advisory Committee on

Evidence Rules, Possible Amendment to Rule 702 (Apr. 1, 2021)

at 11, in Advisory Committee on Evidence Rules Agenda Book

16

To prevent those misstatements from multiplying,

the Advisory Committee amended Rule 702 to “clarify

and emphasize that expert testimony may not be

admitted unless the proponent demonstrates to the

[district] court that it is more likely than not that the

proffered testimony meets the admissibility

requirements set forth in the rule.” Fed. R. Evid. 702

advisory committee’s notes to 2023 amendments

(emphasis added). It did so by adding a clause to note

that expert testimony may be admitted “if the

proponent demonstrates to the court that it is more

likely than not that” Rule 702’s requirements are met.

See H.R. Doc. No. 118-33, at 18.

The 2023 amendment was not intended to (and did

not) change Rule 702’s requirements. Rather, as the

Advisory Committee’s chair explained:

[T]he Committee resolved to respond to

the fact that many courts have declared

that the reliability requirements set

forth in Rule 702(b) and (d)—that the

expert has relied on sufficient facts or

data and has reliably applied a reliable

methodology—are questions of weight

and not admissibility, and more broadly

that expert testimony is presumed to be

admissible. These statements misstate

Rule 702, because its admissibility

requirements must be established to a

90, 100 (Apr. 30,

(emphasis added).

2021),

https://tinyurl.com/mw4u4wum

17

court by a

evidence.[ 9]

preponderance

of

the

In the official notes to the amended Rule, the

Advisory Committee doubled down in explaining that

“weight not admissibility” jurisprudence—including

the Fourth Circuit’s—conflicts with the Federal

Rules:

[M]any courts have held that the critical

questions of the sufficiency of an expert’s

basis, and the application of the expert’s

methodology, are questions of weight

and not admissibility. These rulings are

an incorrect application of Rules 702 and

104(a). . . . Some challenges to expert

testimony will raise matters of weight

rather than admissibility even under the

Rule 104(a) standard. . . . But this does

not mean, as certain courts have held,

that arguments about the sufficiency of

an expert’s basis always go to weight and

not admissibility.

Fed. R. Evid. 702 advisory committee’s notes to 2023

amendments; see also ibid. (“The Committee

concluded that emphasizing the preponderance

standard in Rule 702 specifically was made necessary

9 Memorandum

from Patrick J. Schiltz, Chair, Advisory

Committee on Evidence Rules, to John D. Bates, Chair, Standing

Committee on Rules of Practice and Procedure, Report of the

Advisory Committee on Evidence Rules (May 15, 2022) at 6, in

Committee on Rules of Practice and Procedure Agenda Book 866,

871 (June 7, 2022), https://tinyurl.com/52edk2e2 (emphasis

added).

18

by the courts that have failed to apply correctly the

reliability requirements of that rule.”).

Since the Advisory Committee issued that

clarification, many circuits have correctly followed

the 2023 amendments. See, e.g., Engilis, 151 F.4th at

1047–50 (the 2023 amendments “sought to ‘clarify

and emphasize’ that proffered expert testimony must

meet the admissibility requirements of Rule 702 by a

preponderance of the evidence,” and “that challenges

to an expert’s opinion go to the weight of the evidence

only if a court first finds it more likely than not that

an expert has a sufficient basis to support an opinion”

(emphasis added) (citing Fed. R. Evid. 702 advisory

committee’s note to 2023 amendments)); In re

Onglyza, 93 F.4th at 348 n.7 (“Indeed, Rule 702’s

recent amendments were drafted to correct some

court decisions incorrectly holding ‘that the critical

questions of the sufficiency of an expert’s basis, and

the application of the expert’s methodology, are

questions of weight and not admissibility.’ (quoting

Fed. R. Evid. 702 advisory committee’s note to 2023

amendments)); EcoFactor, 137 F.4th at 1339

(similar); Williams, 143 F.4th at 601 (calling into

question whether expert opinion was “reliably ‘based

on sufficient facts or data’ under Rule 702(b)”);

Nairne, 151 F.4th at 697–98; Sprafka, 139 F.4th at

660–61 (“[A]fter Rule 702’s recent amendment courts

continue to have a gatekeeping role to assure that

evidence admitted in a case is both relevant and

reliable.”).

19

Yet the Fourth Circuit has refused to follow suit.

(So too has the First Circuit. 10) In the decision below,

the Fourth Circuit stayed its wrongheaded course and

reasserted Bresler’s continuing viability in at least

nine federal districts spanning five states. It did so

despite the Advisory Committee’s guidance and

criticism of Bresler, not to mention the text of Rule

702 itself. See also 28 U.S.C. § 2072(a)–(b)

(establishing the primacy of the Federal Rules of

Evidence themselves as the primary authority for

their own interpretation). It even chastised the

district court for performing the very gatekeeping

function that it was required to perform under Rule

702. If a district court cannot perform its gatekeeping

function, then it cannot protect juries from unreliable

expert testimony. And if district courts cannot screen

unreliable expert testimony from juries, a daisy chain

of harms will follow. This circuit split is entrenched,

and this Court’s review would not benefit from further

percolation. It should grant certiorari now to resolve

the split.

III.

ONGOING WEAKENING OF DISTRICT

COURTS’ GATEKEEPING ROLE HARMS

LITIGANTS

AND

THE

JUDICIAL

SYSTEM.

The decision below conflicts with Rule 702’s text,

defies the 2023 amendments, and stands on the

10 Two years ago, the First Circuit made the same mistake,

reaffirming Milward v. Acuity Specialty Products Group, Inc.,

639 F.3d 11 (1st Cir. 2011)—its own version of Bresler—and thus

ensuring that the “weight not admissibility” principle also

remains law in the five federal districts in that circuit.

Rodríguez, 91 F.4th at 70.

20

wrong side of a circuit split. But ultimately and most

practically, it dangerously weakens district courts’

gatekeeping role under Rule 702. The harmful

consequences of such weakening will be felt most

keenly by litigants like amici and their members,

which are often defendants in complex civil litigation

involving expert testimony on both sides.

Because expert testimony can disproportionately

influence juries, the admission of unreliable expert

testimony can unfairly dictate the rest of the

litigation. Defendants that confront adverse expert

rulings may be compelled to settle, rather than take

their chances with a jury, even when there are real

doubts about the science involved. See Margaret A.

Berger, The Admissibility of Expert Testimony, in

Fed. Jud. Ctr., Reference Manual on Scientific

Evidence 11, 19 (3d ed. 2011) (“[A]n inability by the

defendant to exclude plaintiffs’ experts undoubtedly

affects the willingness of the defendant to negotiate a

settlement.”); Rakoff, supra, at 1391 (recounting that

in a mass pharmaceutical products-liability action,

“shortly after my [Daubert] decision came down, most

of the 800 cases settled, for amounts that seemingly

reflected the mid-point nature of what I allowed in the

way of expert testimony”). This dynamic serves only

to perversely incentivize litigants to continue to

proffer speculative and questionable science in

federal courts, contrary to Rule 702’s intention.

In toxic-tort and product-liability cases in

particular, if a plaintiff’s expert testimony is

admitted, “a defendant often feels irresistible

pressure to settle the action rather than risk a battle

of the experts at trial that, if the defendant loses, can

cost exponentially more than the settlement cost of

21

the action.” Christopher R.J. Pace, Admitting and

Excluding General Expert Testimony: The Eleventh

Circuit Construct, 37 Am. J. Trial Advoc. 47, 48

(2013). Those “plaintiffs’ likelihood of success is

commonly driven by the admissibility of their experts’

general causation testimony under Rule 702 of the

Federal Rules of Evidence and Daubert.” Ibid.

The circuit split over the proper application of

Rule 702 also creates the risk of inconsistent verdicts

and encourages forum shopping—particularly in the

mass-tort context. Indeed, following Daubert, the

senior counsel of the Association of Trial Lawyers of

America recommended that, “because it’s difficult to

see light at the end of the Daubert tunnel, plaintiffs

must take another tunnel.” Victor E. Schwartz & Cary

Silverman, The Draining of Daubert and the

Recidivism of Junk Science in Federal and State

Courts, 35 Hofstra L. Rev 217, 269 (2006) (quoting

Ned Miltenberg, Out of the Fire and Into the Fryeing

Pan or Back to the Future, Trial, Mar. 2001, at 24).

But by admitting expert testimony only when it is

shown by a preponderance of the evidence to be

sufficiently reliable to be considered by a jury, district

courts ensure fundamental fairness and bolster public

confidence in our adversarial system of justice. It is

more crucial than ever that district courts carry out

that gatekeeping role with unflinching consistency

because “science in all its forms . . . has in recent

years invaded the courtroom to an unparalleled

extent.” Rakoff, supra, at 1379. Indeed, “[s]cientific

issues” now “permeate the law.” Stephen Breyer,

Introduction, in Fed. Jud. Ctr., Reference Manual on

Scientific Evidence 1, 3 (3d ed. 2011); see also Gen.

Elec. Co., 522 U.S. at 148–49 (Breyer, J., concurring)

22

(given the proliferation in manufactured products, it

is “particularly important to see that judges fulfill

their Daubert gatekeeping function, so that they help

assure that the powerful engine of tort

liability . . . points toward the right substances and

does not destroy the wrong ones”). And yet, as the use

of expert testimony in litigation has proliferated, so

too has “expertise that is fausse and science that is

junky.” Kumho Tire, 526 U.S. at 158–59 (Scalia, J.,

concurring); Joseph M. Price & Gretchen Gates Kelly,

Junk Science in the Courtroom: Causes, Effects and

Controls, 19 Hamline L. Rev. 395, 398 (1996);

Schwartz & Silverman, supra, at 224; Peter Huber,

Junk Science and the Jury, 1990 U. Chi. Legal F. 273,

276–77 (1990). When a district court fails to screen

such unreliable evidence from the jury, it allows false

and misleading evidence to determine real—and often

expensive—outcomes for the litigants.

The Fourth Circuit’s willingness to discard the

gatekeeping function and to punt unreliable expert

testimony to juries undermines the judicial system

and harms litigants (including but not limited to

business defendants) who depend on that system for

fair and accurate determinations of legal liability. The

Fourth Circuit’s defiance of the 2023 amendments to

Rule 702 signals that a deep fissure has opened in this

area of the law—one that is unlikely to close without

this Court’s intervention. Indeed, district courts are

already following the decision below down a path that

further conflicts with Rule 702’s text. See, e.g., In re

Camp Lejeune Water Litig., 2025 WL 3565850, at

*14–25 (E.D.N.C. Dec. 12, 2025) (same and reasoning

that “[t]o accept this argument [for exclusion] would

23

require the court to impermissibly weigh the experts’

methodological inputs rather than the methodology

itself”); Alford v. NFL Player Disability & Survivor

Benefit Plan, 2025 WL 3274428, at *3 (D. Md. Nov.

24, 2025) (“Nevertheless, ‘questions regarding the

factual underpinnings of the [expert witness’] opinion

affect the weight and credibility of the witness’

assessment, not its admissibility.’ The Fourth Circuit

recently held that a trial court committed reversible

error when it ‘waded into credibility determinations’

that were ‘framed as a ‘reliability’ question.’ (first

quoting Bresler, 855 F.3d at 195, and then quoting

Pet.App.26a)); R&J Components Corp. v. Centimark

Corp., 2025 WL 3732157, at *6 (D.S.C. Nov. 18, 2025)

(refusing to exclude expert testimony and citing to

Bresler and the decision below); Michael’s Fabrics,

LLC v. Donegal Mut. Ins. Co., 2025 WL 2624280, at

*4 (D. Md. Sep. 11, 2025) (rejecting challenge “to the

reliability of [expert’s] methodology and resulting

opinion” because “[q]uestions regarding the factual

underpinnings of the [expert witness’] opinion, which

are what Defendant raises here, affect the weight and

credibility of the witness’ assessment, not its

admissibility” (cleaned up) (citing Bresler and

Pet.App.27a n.7)); Mincey v. Se. Farm Equip., 2025

WL 2450913, at *10 (D.S.C. Aug. 26, 2025) (“The

Fourth Circuit has repeatedly explained that

‘questions regarding the factual underpinnings of the

expert witness’ opinion affect the weight and

credibility of the witness’ assessment, not its

admissibility.’” (quoting Pet.App.20a–21a)).

24

CONCLUSION

No circuit should be allowed to flout this Court’s

and the Advisory Committee’s uniform interpretation

of Rule 702 without swift correction by this Court.

This critical issue deserves review by this Court to

confirm the importance of district courts’ gatekeeping

function and the proper evaluation of the reliability of

expert testimony under Rule 702.

The Court should grant the petition for writ of

certiorari.

Respectfully submitted,

JONATHAN D. URICK

KEVIN R. PALMER

U.S. CHAMBER OF

COMMERCE

LITIGATION CENTER

1615 H Street NW

Washington, DC 20062

MATTHEW P. HOOKER

Counsel of Record

WILLIAM W. METCALF

ALSTON & BIRD LLP

1120 S. Tryon Street

Suite 300

Charlotte, NC 28203

(704) 444-1000

matthew.hooker@alston.com

Counsel for Amici Curiae

March 6, 2026

[Additional counsel listed on next page]

25

Additional counsel:

H. SHERMAN JOYCE

LAUREN SHEETS

JARRELL

AMERICAN TORT

REFORM ASSOCIATION

1101 Connecticut

Ave. NW

Suite 400

Washington, DC 20036

SONJA RODMAN

AMERICAN CHEMISTRY

COUNCIL

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Washington, DC 20001

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NATIONAL ASSOCIATION

OF MANUFACTURERS

733 10th Street NW

Suite 700

Washington, D.C. 20001

MICHAELANGELO

FURNARI

AMERICAN FUEL &

PETROCHEMICAL

MANUFACTURERS

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Suite 900N

Washington, DC 20036

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CROPLIFE AMERICA

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Suite 700

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MELISSA B. KIMMEL

PHARMACEUTICAL

RESEARCH AND

MANUFACTURERS OF

AMERICA

670 Maine Ave. SW

Suite 1000

Washington, D.C. 20024

26

MEREDITH B. CODY

RYAN MEYERS

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AMERICAN PETROLEUM

INSTITUTE

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BUSINESS ROUNDTABLE

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