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 a Writ of Certiorari to the

United States Court of Appeals for the Fourth Circuit

BRIEF OF ATLANTIC LEGAL FOUNDATION

AS AMICUS CURIAE

IN SUPPORT OF PETITIONERS

Robert E. Johnston

Lawrence S. Ebner

A leksandra Rybicki

Counsel of Record

A lexa D. Halkias

Atlantic Legal Foundation

Hollingsworth LLP

1701 Pennsylvania Ave., NW

1350 I Street, NW

Washington, DC 20006

Washington, DC 20005

(202) 729-6337

lawrence.ebner@atlanticlegal.org (202) 898-5800

rjohnston@hollingsworthllp.com

arybicki@hollingsworthllp.com

ahalkias@hollingsworthllp.com

Counsel for Amicus Curiae

120927

A

(800) 274-3321 • (800) 359-6859

i

TABLE OF CONTENTS

Page

TABLE OF AUTHORITIES ........................................ii

INTEREST OF THE AMICUS CURIAE ................... 1

SUMMARY OF ARGUMENT ..................................... 2

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

A. The drafting history and plain language of the

2023 amendments to Rule 702 reinforce district

courts’ gatekeeping role ......................................... 5

1. Amended Rule 702 clarifies that the

sufficiency of an expert’s basis and the

application of the expert’s methodology are

questions of admissibility for the judge to be

established by the preponderance of the

evidence ............................................................. 9

2. Amended Rule 702 clarifies that the

application of an expert’s methodology, as well

as the methodology itself, must be reliable ... 11

B. The standard applied by the Fourth Circuit is

directly at odds with amended Rule 702 ............. 13

C. This Court’s intervention is needed to correct and

end the already-present trickle-down effect of the

Fourth Circuit’s misapplication of Rule 702 ....... 16

CONCLUSION .......................................................... 21

ii

TABLE OF AUTHORITIES

Page(s)

Cases

Alford v. NFL Player Disability & Survivor

Benefit Plan,

No. CV JRR-23-358, 2025 WL 3274428

(D. Md. Nov. 24, 2025) ...................................... 19

Amchem Prods. v. Windsor,

521 U.S. 591 (1997) ............................................. 8

Bresler v. Wilmington Trust,

855 F.3d 178 (4th Cir. 2017) ..... 3, 4, 7, 13, 14, 18

In re Camp Lejeune Water Litig.,

No. 7:23-CV-897, 2025 WL 3565850

(E.D.N.C. Dec. 12, 2025) ................................... 18

Class v. United States,

583 U.S. 174 (2018) ......................................... 8, 9

Daubert v. Merrell Dow Pharms., Inc.,

509 U.S. 579 (1993) ............................. 4, 8, 11, 17

General Electric Co. v. Joiner,

522 U.S. 136 (1997) ............................... 15, 18, 19

Kumho Tire Co. v. Carmichael,

526 U.S. 137 (1999) ............................... 11, 18, 19

iii

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

No. 1:24-CV-01585-JRR, 2025 WL

2624280 (D. Md. Sep. 11, 2025) ........................ 18

Mincey v. Se. Farm Equip., Co.,

No. 4:23-CV-01050-JD, 2025 WL

2450913 (D.S.C. Aug. 26, 2025) ........................ 18

Moore v. Barnes,

802 F. Supp. 3d 792 (E.D.N.C. 2025)................ 19

State v. O’Key,

899 P.2d 663 (Or. 1995) .................................... 11

Tome v. United States,

513 U.S. 150 (1995) ............................................. 8

United States v. Vonn,

535 U.S. 55 (2002) ............................................... 8

Waetzig v. Halliburton Energy Servs.,

604 U.S. 305 (2025) ............................................. 8

Williams v. Sig Sauer, Inc.,

799 F. Supp. 3d 470 (E.D.N.C. 2025)................ 19

Statutes

28 U.S.C. § 2072 ....................................................... 3

Rules

Fed. R. Evid. 104 ..................................... 8-10, 12, 13

Fed. R. Evid. 702 ...........................1-13, 15-17, 19-20

iv

Other Authorities

Advisory Comm. on Evidence Rules,

Minutes of the Meeting of April 26-27,

2018, https://tinyurl.com/5n7p9jdm ................... 8

Advisory Comm. on Evidence Rules,

Minutes of the Meeting of May 6, 2022,

https://tinyurl.com/28k8j9fu ............................. 10

Advisory Comm. on Evidence Rules,

Minutes of the Meeting of Nov. 13, 2020,

https://tinyurl.com/yc59b94b .............................. 7

Advisory Comm. on Evidence Rules,

Memorandum from Daniel J. Capra,

Rep., to Advisory Comm. on Evidence

Rules (Oct. 21, 2016),

https://tinyurl.com/9x9jk6ff ................................ 6

Brief of Appellant, Williams v. Sig Sauer,

Inc., No. 25-2196, 2026 WL 173025 (4th

Cir. Jan. 21, 2026) ............................................. 19

Colleen Cochran, The Process, Progression,

and Potential Ramifications of the Rule

702 Amendment, A.B.A. (Sep. 5, 2022)............. 12

David E. Bernstein & Eric G. Lasker,

Defending Daubert: It’s Time to Amend

Federal Rule of Evidence 702, 57 Wm. &

Mary L. Rev. 1 (2015).......................................... 6

v

Fed. R. Evid. 702 advisory committee’s

notes to 2023 amendments .. 3, 5, 9-10, 13, 15, 19

Fed. R. Evid. 702 advisory committee’s

notes to 2000 amendments ............................... 11

Federal Rules of Evidence—Expert

Testimony—Judicial Conference Amends

Rule 702—Federal Rule of Evidence 702,

138 Harv. L. Rev. 899 (2025) ...................... 17, 20

Hon. Patrick J. Schiltz, Report of the

Advisory Comm. on Evid. Rules (May 15,

2022), https://tinyurl.com/yu6f299b ........... 13, 15

Int’l Ass’n of Def. Couns., New Federal Rule

of Evidence Rule 702: A Circuit-byCircuit Guide to Overruled “Wayward

Caselaw” (Eric Lasker & Joshua Leader

eds., 2024), https://tinyurl.com/4n3cxax2........... 6

Lee Mickus, Amended Rule 702 in 2025:

Circuit Courts Embrace the Changed

Standard, Wash. Legal Found. (Oct. 8,

2025), https://tinyurl.com/mt9vf4pp ........... 17, 18

Letters from U.S. Sup. Ct. C.J. John G.

Roberts, Jr. to Hon. Kevin McCarthy,

Speaker, U.S. House of Reps., and Hon.

Kamala Harris, President, U.S. Senate

(Apr. 24, 2023),

https://tinyurl.com/s82hzvnd .............................. 5

vi

Nat’l Academies Scis., Eng’g, & Med. and

Fed. Jud. Ctr., Reference Manual on

Scientific Evidence (“Ref. Manual”) (4th

ed. 2025) ........................................................ 5, 14

Peter Huber, Junk Science and the Jury,

1990 U. Chi. Legal F. 273 (1990) ...................... 11

Thomas D. Schroeder, Toward a More

Apparent Approach to Considering the

Admission of Expert Testimony, 95 Notre

Dame L. Rev. 2039 (2020) ......................... 3, 4, 13

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) .............. 11

1

INTEREST OF THE AMICUS CURIAE 1

Established in 1977, the Atlantic Legal Foundation

(ALF) is a national, nonprofit, nonpartisan, public

interest law firm. ALF’s mission for the past five

decades has been to advance the rule of law and civil

justice by advocating for individual liberty, free

enterprise, property rights, limited and responsible

government, sound science in judicial and regulatory

proceedings, and effective education, including

parental rights and school choice. With the benefit of

guidance from the distinguished legal scholars,

corporate legal officers, private practitioners, business

executives, and prominent scientists who serve on its

Board of Directors and Advisory Council, ALF pursues

its mission by participating as amicus curiae in

carefully selected appeals before the Supreme Court,

federal courts of appeals, and state supreme courts.

See atlanticlegal.org.

***

The Court should grant certiorari to prevent the

widespread judicial chaos that the Fourth Circuit’s

ruling in this case, unless reversed, will engender.

Doing so will ensure that all federal courts properly

apply Federal Rule of Evidence 702, as amended in

December 2023, especially adherence to the rule’s

Petitioners’ and Respondent’s counsel were provided timely

notice of this brief in accordance with Supreme Court Rule 37.2.

No counsel for a party authored this brief in whole or part, and

no party, counsel for a party, or person other than the amicus

curiae and its counsel made a monetary contribution intended to

fund preparation or submission of this brief.

1

2

expert testimony admissibility standards as set forth

in the amended rule’s text and accompanying advisory

committee notes. The Court needs to grant review to

rein in courts (like the Fourth Circuit here) that refuse

to grapple with the clarifying amendments and

instead rely on outdated and inapplicable case law.

Uniformity in lower courts’ application of amended

Rule 702 is needed to ensure that all litigants operate

on the same playing field regardless of the federal

circuit in which their cases are heard. Reversing the

Fourth Circuit’s erroneous interpretation of amended

Rule 702 will do just that by ensuring consistency in

courts’ application of the rule’s expert admissibility

standards: specifically, that challenges to the factual

basis of an expert witness’s testimony go to weight

only if a district judge first finds it more likely than

not that an expert has a sufficient basis to support the

testimony.

The origin, purpose, and intended impact of

amended Rule 702 all underscore the need for the

Court’s review. A ruling by this Court that the Fourth

Circuit applied an archaic admissibility standard that

directly contradicts the amended rule will create

essential coherence in the federal courts and prevent

circuit splits that existed under the prior version of the

rule.

SUMMARY OF ARGUMENT

The Fourth Circuit’s holding in Sommerville that

an expert’s selection of data input into the expert’s

methodology is a question “affect[ing] the weight and

credibility of the witness’ assessment, not its

3

admissibility,” contravenes amended Rule 702 and the

advisory committee’s notes that this Court approved

and Congress allowed to take effect. Pet. App. 20a-22a.

As explicitly explained in the advisory committee’s

notes adopted alongside the 2023 amendments,

decisions regarding an expert’s methodology based on

“questions of weight and not admissibility . . . are an

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

Evid. 702 advisory committee’s notes to 2023

amendments.

As adopted, the 2023 amendments clarify that:

(1) the court, not jury, must apply a preponderance-ofthe-evidence standard to each of the reliability

requirements of Rule 702 at the admissibility stage;

and (2) the court, as gatekeeper, must find that an

expert’s methodology, and the application thereof, is

reliable by a preponderance-of-the-evidence. Fed. R.

Evid. 702. It follows that the judge must determine

whether an expert’s “testimony is based on sufficient

facts or data,” among the other reliability

requirements, per Rule 702(b). Id. Once amended Rule

702 went into effect on December 1, 2023, any case law

in conflict has “no further force or effect.” 28 U.S.C. §

2072(b).

The Fourth Circuit ignored the 2023 amendments

cited in petitioners’ merits brief, Pet. at 30, and

instead relied on Bresler v. Wilmington Trust, 855

F.3d 178, 195 (4th Cir. 2017) as precedent for the

admissibility standard in that circuit. But in

promulgating the 2023 amendments, the advisory

committee members criticized cases like Bresler for

misstating the admissibility standard. In fact, as

4

discussed infra section B, Judge Thomas Schroeder,

Chair of the Subcommittee that drafted the 2023

amendments, specifically called out Bresler for being

inconsistent with the standards set forth in the rule.

The Fourth Circuit’s recycling of its Bresler

standard is irreconcilable with the text and purpose of

amended Rule 702 and the standards adopted by the

Fifth, Sixth, Eighth, Ninth, and Federal Circuits. See

Pet. at 12-25. In holding that the factual

underpinnings of an expert’s opinion go to the weight

jurors should give to that evidence, not to the

threshold question of its admissibility, the Fourth

Circuit took the same obdurate approach as the First

Circuit, creating a circuit split that remains

unchecked despite the amendments’ clarification of

the uniform standard. Id. (discussing the circuit split).

This Court has ruled that the admissibility of

expert testimony is governed by Rule 702, not by case

law. Daubert v. Merrell Dow Pharms., Inc., 509 U.S.

579, 587 (1993). Because of the misapplication of

amended Rule 702, the Court should emphasize that

lower courts should take a fresh look at expert

admissibility requirements in light of the 2023

amendments. This is needed to achieve consistency

among trial courts, particularly since the rule change

was precipitated by analyses demonstrating that

many courts had been applying the rule incorrectly.

This Court should grant certiorari to correct the

already-present downstream effects of the Fourth and

First Circuit’s misapplications of Rule 702, including

those in circuits that have not yet grappled with the

question presented (the Second, Third, Seventh,

5

Tenth, Eleventh, and District of Columbia Circuits). A

ruling by this Court will provide clear guidance

regarding the proper interpretation of Rule 702 and

harmonize the standard on the admissibility of expert

testimony across all circuits.

ARGUMENT

A. The drafting history and plain language of

the 2023 amendments to Rule 702

reinforce district courts’ gatekeeping role

On December 1, 2023, Rule 702 was amended with

the approval of the Supreme Court and without any

changes from Congress in response to the

determination of the standing committee’s advisory

committee on evidence rules (“advisory committee”)

that many courts were applying the rule incorrectly,

including by misstating, ignoring, or relaxing the

admissibility standard. 2 See Fed. R. Evid. 702

advisory committee’s notes to 2023 amendments; see

also Nat’l Academies Scis., Eng’g, & Med. and Fed.

Jud. Ctr., Reference Manual on Scientific Evidence

(“Ref. Manual”) 13 (4th ed. 2025) (recognizing that

amended Rule 702 was “designed to correct

misapplications of the rule”).

2 The amendments to Rule 702 automatically took effect on

December 1, 2023, after Congress did not reject or modify the

proposed amendments. See generally Letters from U.S. Sup. Ct.

C.J. John G. Roberts, Jr. to Hon. Kevin McCarthy, Speaker, U.S.

House of Reps., and Hon. Kamala Harris, President, U.S. Senate

(Apr. 24, 2023), https://tinyurl.com/s82hzvnd (adopting and

transmitting the proposed amendments to Rule 702 to Congress).

6

The issue of courts misapplying the standard was

brought to the committee’s attention after a law

review article demonstrated that “many courts

continue to resist the judiciary’s proper gatekeeping

role, either by ignoring Rule 702’s mandate altogether

or by aggressively reinterpreting the Rule’s

provisions.” David E. Bernstein & Eric G. Lasker,

Defending Daubert: It’s Time to Amend Federal Rule

of Evidence 702, 57 Wm. & Mary L. Rev. 1, 8-9, 48

(2015) (surveying cases and concluding that a number

of courts were not following the 2000 amendments). 3

The reporter to the advisory committee, Daniel J.

Capra, specifically identified a pervasive problem of

“wayward caselaw” in which federal courts had been

“far more lenient about admitting expert testimony

than any reasonable reading of the Rule would

allow.” 4 Professor Capra went on to conclude that

“courts have defied the Rule’s requirements” and he

lamented that the Evidence Rules were being

“disregarded by courts.” 5

3 More recent analyses have identified that the problem persists.

See generally Int’l Ass’n of Def. Couns., New Federal Rule of

Evidence Rule 702: A Circuit-by-Circuit Guide to Overruled

“Wayward Caselaw” (Eric Lasker & Joshua Leader eds., 2024),

https://tinyurl.com/4n3cxax2 (listing cases misapplying Rule 702

in each circuit).

4 Advisory Comm. on Evidence Rules, Memorandum from Daniel

J. Capra, Rep., to Advisory Comm. on Evidence Rules, 262 (Oct.

21, 2016), https://tinyurl.com/9x9jk6ff.

5 Id. at 268, 271.

7

The 2023 amendments to Rule 702 are the product

of the committee’s eight years of extensive analyses,

which revealed that in a “number of federal cases . . .

judges did not apply the preponderance standard of

admissibility to [Rule 702’s] requirements of

sufficiency of basis and reliable application of

principles and methods, instead holding that such

issues were ones of weight for the jury.” 6 This finding

applies to Bresler, upon which the Fourth Circuit

relied here.

The committee advanced to this Court the

“clarifying amendment” to remedy concerns that

“federal cases and comments from members of the

public had revealed a pervasive problem with courts

discussing expert admissibility requirements as

matters of weight.” 7 The minutes indicate that the

drafters intended to reduce the likelihood that trial

courts would “kick difficult Rule 702 questions to the

jury.” 8 The Committee Chair, Hon. Patrick J. Schiltz,

stated that “Circuit court language at odds with the

language of Rule 702 present[ed] a serious concern”

that justified intervention despite initial “trepidation

about sending an unusual amendment clarifying an

existing rule to the Supreme Court.” 9

6 Advisory Comm. on Evidence Rules, Minutes of the Meeting of

Nov. 13, 2020, at 3, https://tinyurl.com/yc59b94b.

7 Id. at 4.

8 Id.

9 Id. at 5.

8

The advisory committee found that the rule should

require the “trial judge [to] make a finding by a

preponderance of the evidence on the admissibility

requirements before allowing the expert to testify, and

that it would be error to permit the testimony if the

judge is not satisfied that the expert’s basis is

sufficient” because “the admissibility requirements in

Rule 702 are clearly governed by Rule 104(a) --- as also

stated in Daubert itself.” 10

The amendment’s purpose is reflected both in the

advisory committee’s notes accompanying the rule and

in the advisory committee’s working papers and

publications. Advisory committee notes are afforded

considerable weight because they provide the most

succinct and readily accessible guide to the proper

application of federal court rules. 11 Published

10 Advisory Comm. on Evidence Rules, Minutes of the Meeting of

April 26-27, 2018, at 11-12, https://tinyurl.com/5n7p9jdm

(addressing hypothetical where an expert “rejects 7 of 10 seminal

studies in an area and [relies] on the 2 or 3 minority studies in

the field as the basis for his opinion” and concluding the opinion

should be excluded).

11 This Court has relied upon such notes to interpret the federal

rules. See, e.g., Waetzig v. Halliburton Energy Servs., 604 U.S.

305, 312 (2025) (relying on “the Federal Rules Advisory

Committee’s Notes, which are a reliable source of insight into the

meaning of a rule”) (citation modified); United States v. Vonn, 535

U.S. 55, 64 n.6 (2002) (“[T]he Advisory Committee Notes provide

a reliable source of insight into the meaning of a rule, especially

when, as here, the rule was enacted precisely as the Advisory

Committee proposed.”); Tome v. United States, 513 U.S. 150, 160

(1995) (similar). Records reflecting the committee’s deliberations

9

alongside the rules themselves, the notes are subject

to the same rule-making process, public notice and

comment, and Supreme Court and congressional

review and approval as the rules themselves. See

Class v. United States, 583 U.S. 174, 188 n.2 (2018)

(Alito, J., dissenting) (“Advisory Committee’s Notes

are adopted by the committee that drafts the rule; they

are considered by the judicial conference when it

recommends promulgation of the rule; they are before

this Court when we prescribe the rule under the Rules

Enabling Act . . . .”).

1. Amended Rule 702 clarifies that the

sufficiency of an expert’s basis and the

application of the expert’s methodology

are questions of admissibility for the

judge to be established by the

preponderance of the evidence

The 2023 amendment eliminates any doubt that

Rule 104(a)’s preponderance standard applies to

expert testimony in its totality by inserting language

on the preponderance-of-the-evidence standard

directly into Rule 702. See Fed. R. Evid. 702 advisory

committee’s notes to 2023 amendments (“[M]ore likely

than not . . . is the preponderance of the evidence

standard that applies to most of the admissibility

requirements set forth in the evidence rules.”). The

amendment served “to clarify and emphasize that

expert testimony may not be admitted unless the

have also been used to guide the Court’s interpretations. See, e.g.,

Amchem Prods. v. Windsor, 521 U.S. 591, 613-20 (1997) (“Courts

are not free to amend a rule outside the process Congress

ordered.”).

10

proponent demonstrates to the court that it is more

likely than not that the proffered testimony meets the

admissibility requirements set forth in the rule.” Id.

The advisory committee note “clarifies that the

preponderance standard applies to the three

reliability-based requirements . . . that many courts

have incorrectly determined to be governed by the

more permissive Rule 104(b) standard,” and further

admonishes the “many courts [that] 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” as “an

incorrect application of Rule 702 and 104(a).” Id.

The amendment also explicitly inserted “the court”

directly into the text of the rule to emphasize that the

court, and not the jury, determines whether reliability

is met. See Fed. R. Evid. 702. The committee included

this clarification to address “confusion about the

respective roles of judge and jury in deciding the

admissibility of expert testimony.” 12

The advisory committee emphasized that the

judicial gatekeeping responsibility “is essential

because just as jurors may be unable, due to lack of

specialized knowledge, to evaluate meaningfully the

reliability of scientific and other methods underlying

expert opinion, jurors may also lack the specialized

knowledge to determine whether the conclusions of an

expert go beyond what the expert’s basis and

12 Advisory Comm. on Evidence Rules, Minutes of the Meeting of

May 6, 2022, at 7, https://tinyurl.com/28k8j9fu.

11

methodology may reliably support.” Fed. R. Evid. 702

advisory committee’s notes to 2023 amendments.

Expert evidence “that does not meet the judicial

standard for scientific validity can mislead, confuse,

and mystify the jury.” 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, 220 (2006) (quoting

State v. O’Key, 899 P.2d 663, 678 n.20 (Or. 1995)).

Allowing expert testimony based on insufficient facts

or data to go before the jury creates the risk that the

jury may nonetheless find it sufficient simply because

it is offered by an expert rather than a lay person. See

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

Legal F. 273, 276-277 (1990). That is impermissible

under Rule 702.

2. Amended Rule 702 clarifies that the

application of an expert’s methodology,

as well as the methodology itself, must

be reliable

Rule 702’s amendments in 2000 required courts to

determine whether an expert had “unjustifiably

extrapolated from an accepted premise to an

unfounded conclusion.” Fed. R. Evid. 702 advisory

committee’s notes to 2000 amendments. 13 In 2023, the

13 The 2000 amendments were enacted in response to Daubert

and Kumho Tire Co. v. Carmichael, 526 U.S. 137 (1999), to

“affirm[] the trial court’s role as gatekeeper[,] . . . provide[] some

general standards that the trial court must use to assess the

12

amended portion of Rule 702(d) resolved any lingering

confusion on these issues by explicitly empowering the

court to evaluate the reliability of the conclusions that

the expert has drawn from her methodology by a

preponderance-of-the-evidence.

The 2023 amendments to Rule 702 make clear that

it is not enough for an expert to have a reliable

methodology to pass muster under Rule 702—the

court also must analyze and determine that the

expert’s opinions support a reliable application of a

reliable methodology “to the facts of the case,” by a

preponderance-of-the-evidence. Fed. R. Evid. 702(d).

Specifically, the amendments instruct the court to

analyze the reliability of both aspects of the

methodology on which the expert’s opinion is based to

safeguard “against overstated conclusions by directing

judges to ensure that experts’ opinions result from

reliable methodologies that are reliably applied.” 14

The Standing Committee further stressed the

importance of reliable application of an expert’s

methodology under Rule 702(d):

The language of the amendment more

clearly empowers the court to pass

judgment on the conclusion that the

reliability and helpfulness of proffered expert testimony,” and

recognize that “the admissibility of all expert testimony is

governed by the principles of Rule 104(a).” Fed. R. Evid. 702

advisory committee’s notes to 2000 amendments.

Colleen Cochran, The Process, Progression, and Potential

Ramifications of the Rule 702 Amendment, A.B.A. (Sep. 5, 2022),

https://tinyurl.com/2rack4tx.

14

13

expert has drawn from the methodology.

Thus the amendment is consistent with

General Electric Co. v. Joiner, 522 U.S.

136 (1997), in which the Court declared

that a trial court must consider not only

the expert’s methodology but also the

expert’s conclusion; that is because the

methodology must not only be reliable, it

must be reliably applied. 15

The advisory committee’s note elaborated that Rule

702(d) was amended “to emphasize that each expert

opinion must stay within the bounds of what can be

concluded from a reliable application of the expert’s

basis and methodology.” Fed. R. Evid. 702 advisory

committee’s notes to 2023 amendments.

B. The standard applied by the Fourth

Circuit is directly at odds with amended

Rule 702

The Fourth Circuit in Sommerville solely relied on

pre-amendment case law, specifically Bresler, 855

F.3d at 195, which directly conflicts with amended

Rule 702. The Chairman of the subcommittee on Rule

702 has expressly identified Bresler as a case that the

revisions were intended to change because it

“effectively vitiated the application of [the

preponderance requirement in] Rule 104(a) to Rule

702(b).” Thomas D. Schroeder, Toward a More

Apparent Approach to Considering the Admission of

15 Hon. Patrick J. Schiltz, Report of the Advisory Comm. on Evid.

Rules, at 6 (May 15, 2022), https://tinyurl.com/yu6f299b.

14

Expert Testimony, 95 Notre Dame L. Rev. 2039, 204344, 2049-50 (2020) (critiquing Bresler among “a

sampling of illustrative cases that have been

identified to the Advisory Committee” that “misstate

and/or misapply” the preponderance standard).

There is no doubt that the drafters of Rule 702 and

the advisory committee notes intended to preclude

further application of Bresler and other cases that

include the same erroneous analysis. See Ref. Manual

at 13 (“Judges and litigants should exercise caution in

relying on pre-amendment cases . . . because the 2023

amendment was designed to correct misapplications of

the rule . . . .”).

The district court below used its gatekeeping

discretion and properly excluded the testimony of

respondent’s expert witness, Dr. Ranajit Sahu, finding

it was not grounded in reliable facts and data. See Pet.

App. 42a-88a. Using an air model, Dr. Sahu calculated

respondent’s potential cumulative exposure to

ethylene oxide from petitioners’ facilities during the

relevant time period. The district court identified

several substantive issues with Dr. Sahu’s selected

inputs for his model—including source data, receptor

data, and meteorological data—and aptly found that

his application of the data to the facts “was

methodologically flawed, full of unsubstantiated

assumptions, and not scientifically sound.” Pet. App.

88a.

On appeal, the Fourth Circuit incorrectly

determined that because the air model itself is a

reliable methodology, the jury, and not the judge,

should then be responsible for issues related to the

15

data variables that Dr. Sahu input into the air model.

This is exactly the type of argument that the advisory

committee rejected during its consideration of the

2023 amendments. The committee made clear that the

court must pass judgment on the validity of the

methodology applied to generate the conclusion that

the expert reached—indeed, this is the Court’s job as

gatekeeper under Rule 702. 16 But in de novo fashion,

the Fourth Circuit rejected the district court’s findings

and substituted its own analysis without engaging in

any way with the plain text or notes of Amended Rule

702. The Supreme Court could reverse the Fourth

Circuit’s decision on this basis alone. See, e.g., Gen.

Elec. Co. v. Joiner, 522 U.S. 136, 141-43 (1997)

(reversing expert admissibility decision that “failed to

give the trial court the deference that is the hallmark

of abuse-of-discretion review”).

The Fourth Circuit held that challenges to the

“factual underpinnings” of an expert’s testimony will

always be a question for the jury to resolve. Pet. App.

20a-21a. This directly contradicts Rule 702 as the

2023 amendments sought to “clarify and emphasize

that expert testimony may not be admitted” unless its

proponent can show, by a preponderance of the

evidence, that it satisfies each of the rule’s

admissibility requirements. Fed. R. Evid. 702 advisory

committee’s notes to 2023 amendments (emphasis

added). The committee recognized that sometimes

such questions could go to the weight of evidence—but

16 See Hon. Patrick J. Schiltz, Report of the Advisory Comm. on

Evid. Rules, at 6 (May 15, 2022), https://tinyurl.com/yu6f299b.

16

they could do so only “once the court has found it more

likely than not that the admissibility requirement has

been met.” Id. 17

To comply with amended Rule 702, the district

court below was required to assess the reliability of the

methodology (i.e., the air model) and Dr. Sahu’s

application of the underlying facts and data to the

methodology (i.e., whether Dr. Sahu reliably selected

data inputs for the model). The district court did just

that. Pet. App. 42a-88a.

C. This Court’s intervention is needed to

correct and end the already-present

trickle-down effect of the Fourth Circuit’s

misapplication of Rule 702

Courts cannot simply choose which rules to follow

and which to ignore. The Fourth Circuit’s decision to

ignore the 2023 amendments cannot be allowed to

stand. All courts should be aligned with the

application of Rule 702 and the accompanying

advisory committee notes approved by this Court and

allowed to become active by Congress. See Pet. at 1225. District courts frequently face challenges to expert

testimony and any misapplication of the admissibility

standard results in serious consequences that can

impact the disposition of the case. Such consequences

are ever present where, as here, the circuit court

17 As Chief Judge Albert Diaz dissented, “an expert who

constructs a model based on faulty assumptions and irrelevant

data shouldn’t be handed a ‘get-out-of-Daubert-free card’ simply

because he uses an otherwise reliable modeling system.” Pet.

App. 35a.

17

creates binding authority that can misguide lower

courts’ application of an incorrect standard while

simultaneously diluting the discretion afforded to the

district court judge on appeal.

As the commentary to Rule 702 continues to be

ignored by the First and Fourth Circuits, this Court

must step in and provide the guidance necessary to

instill consistent application of Rule 702 across

circuits and district courts, and to prevent further

courts from mistakenly admitting unreliable expert

testimony. See Mark A. Behrens & Andrew J. Trask,

Federal Rule of Evidence 702: A History and Guide to

the 2023 Amendments Governing Expert Evidence, 12

Tex. A&M L. Rev. 43, 75 (2024) (recognizing that the

Court must step in if circuit courts do not follow the

law).

Absent Supreme Court intervention, “litigants in

cases involving complex scientific issues . . . may face

expert testimony which does not meet the standard set

out by Rule 702.” Federal Rules of Evidence—Expert

Testimony—Judicial Conference Amends Rule 702—

Federal Rule of Evidence 702, 138 Harv. L. Rev. 899,

906 (2025) (“Judicial Conference Amends Rule 702”)

(explaining that “more than twenty years after

Daubert, the Supreme Court will need to take up the

issue directly if it wishes for lower courts to coalesce

around one approach”).

One of the dangers of the Fourth Circuit’s decision

in Sommerville is its immediate impact on the district

18

court decisions below. 18 Several district courts have

already followed Sommerville and consequently have

refused to consider the reliability and sufficiency of an

expert’s opinions at the admissibility stage. See, e.g.,

In re Camp Lejeune Water Litig., No. 7:23-CV-897,

2025 WL 3565850, at *23 (E.D.N.C. Dec. 12, 2025)

(relying on Sommerville’s holding that questions

regarding the factual basis of an expert’s opinion go to

weight rather than admissibility); Michael’s Fabrics,

LLC v. Donegal Mut. Ins., No. 1:24-CV-01585-JRR,

2025 WL 2624280, at *4 (D. Md. Sep. 11, 2025) (first

citing Bresler, 85 F.3d at 195; then citing

Sommerville, 149 F.4th at 427) (similar); Mincey v. Se.

Farm Equip., Co., No. 4:23-CV-01050-JD, 2025 WL

2450913, at *10 (D.S.C. Aug. 26, 2025) (first quoting

Sommerville, 149 F.4th at 423; then quoting Bresler,

855 F.3d at 195) (similar).

A prompt ruling from this Court is needed to

counteract the immediate negative effects of the

Fourth Circuit’s decision on lower courts. Otherwise,

litigants will continue to face uncertainty in how Rule

702 should be applied, admissibility standards that

vary by circuit, and the same wayward decisions that

necessitated the rule’s amendments.

The Fourth Circuit’s decision in Sommerville also

applied a standard of appellate review that affords no

18 See Lee Mickus, Amended Rule 702 in 2025: Circuit Courts

Embrace the Changed Standard, Wash. Legal Found. (Oct. 8,

2025), https://tinyurl.com/mt9vf4pp (reporting the consequences

of Sommerville’s immediate influence on district courts in the

Fourth Circuit).

19

deference to district courts’ gatekeeping decisions and

contradicts the standard established by this Court. 19

The panel’s decision signals to district courts deciding

to properly apply amended Rule 702 that their

deference will not survive appellate review.

District courts in the Fourth Circuit that have

decided to follow amended Rule 702 are at risk of the

same de novo review and reversal on appeal. See, e.g.,

Williams v. Sig Sauer, Inc., 799 F. Supp. 3d 470, 483–

84 (E.D.N.C. 2025) (applying the preponderance

standard to “questions of the sufficiency of an expert’s

basis, and the application of the expert’s

methodology”) (quoting Fed. R. Evid. 702 advisory

committee’s notes to 2023 amendments); 20 Moore v.

Barnes, 802 F. Supp. 3d 792, 823 (E.D.N.C. 2025)

(same); Alford v. NFL Player Disability & Survivor

Benefit Plan, No. CV JRR-23-358, 2025 WL 3274428,

at *18 (D. Md. Nov. 24, 2025) (finding expert’s lack of

a sufficient basis for his proffered opinions bore

“directly on admissibility, not the weight of the

See Gen. Elec. Co., 522 U.S. at 143 (district courts’ expert

admissibility decisions must be given deference under the abuse

of discretion standard); Kumho Tire Co., 526 U.S. at 152 (“[T]he

trial judge must have considerable leeway in deciding in a

particular case how to go about determining whether particular

expert testimony is reliable.”).

19

20 The district court’s exclusion of two experts has already been

appealed. See Brief of Appellant, Williams v. Sig Sauer, Inc., No.

25-2196, 2026 WL 173025, at *7 (4th Cir. Jan. 21, 2026) (arguing

that the district court erred because the “matters relied upon by

the Court as its basis for excluding… pertain[ed] to the weight of

the evidence and testimony, not its admissibility”).

20

proffered evidence”). Such appeals are already before

the Fourth Circuit.

Without Supreme Court intervention, the Fourth

Circuit’s misapplication of Rule 702 will continue to

poison the well of the circuit’s cases. The Fourth

Circuit’s continued refusal to adhere to amended Rule

702 demonstrates that “the Supreme Court will need

to take up the issue directly if it wishes for lower

courts to coalesce around one approach.” Judicial

Conference Amends Rule 702, 138 Harv. L. Rev. at 906.

21

CONCLUSION

The petition for a writ of certiorari should be

granted.

Respectfully submitted,

LAWRENCE S. EBNER

Counsel of Record

ATLANTIC LEGAL FOUNDATION

1701 Pennsylvania Ave., NW

Washington, DC 20006

(202) 729-6337

lawrence.ebner@atlanticlegal.org

ROBERT E. JOHNSTON

ALEKSANDRA RYBICKI

ALEXA D. HALKIAS

HOLLINGSWORTH LLP

1350 I Street, NW

Washington, DC 20005

(202) 898-5800

RJohnston@Hollingsworthllp.com

ARybicki@Hollingsworthllp.com

AHalkias@Hollingsworthllp.com

Counsel for Amicus Curiae

March 2026