Petition for Writ of Certiorari — Union Carbide Corporation, et al., Petitioners v. Lee Ann Sommerville
Supreme Court briefFeb 2, 2026
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No. _____
IN THE
Supreme Court of the United States
____________________
UNION CARBIDE CORPORATION; COVESTRO LLC,
Petitioners.
v.
LEE ANN SOMMERVILLE, individually, and on behalf
of all others similarly situated,
Respondent.
____________________
On Petition for a Writ of Certiorari to the
U.S. Court of Appeals for the Fourth Circuit
____________________
PETITION FOR A WRIT OF CERTIORARI
____________________
JOHN L. EWALD
SUSANNA MOLDOVEANU
KIRKLAND & ELLIS LLP
601 Lexington Avenue
New York, NY 10022
(212) 446-4800
DAVID A. FUSCO
WESLEY A. PRICHARD
T. NATHAN TOWNSEND
K&L GATES LLP
210 Sixth Avenue
Pittsburgh, PA 15222
(412) 355-6500
DONALD B. VERRILLI, JR.
Counsel of Record
ELAINE J. GOLDENBERG
RACHEL G. MILLER-ZIEGLER
KYLE A. SCHNEIDER
MUNGER, TOLLES & OLSON LLP
601 Massachusetts Ave. NW
Suite 500E
Washington, DC 20001-5369
(202) 220-1100
Donald.Verrilli@mto.com
Counsel for Petitioners
i
QUESTION PRESENTED
Whether, under Federal Rule of Evidence 702,
challenges to the factual basis of an expert witness’s
testimony always go to the weight of the evidence rather than to admissibility, as the First and Fourth Circuits hold, or whether such challenges go to weight
only if a court first finds it more likely than not that
an expert has a sufficient basis to support the testimony, as the Fifth, Sixth, Eighth, Ninth, and Federal
Circuits hold.
ii
PARTIES TO THE PROCEEDINGS
Petitioners Union Carbide Corporation and
Covestro LLC were defendants in the district court
and appellees in the court of appeals.
Respondent Lee Ann Sommerville, individually,
and on behalf of all others similarly situated, was the
plaintiff in the district court and appellant in the court
of appeals.
iii
RULE 29.6 STATEMENT
Petitioner Union Carbide Corporation is a wholly
owned subsidiary of The Dow Chemical Company,
which is a wholly owned subsidiary of Dow Inc. Dow
Inc. is a publicly held company. The Vanguard Group
owns more than 10% of the stock of Dow Inc.
Petitioner Covestro LLC is a wholly owned subsidiary of Covestro (Netherlands) B.V., and that entity is
a wholly owned subsidiary of Covestro Deutschland
AG. Covestro Deutschland AG is a wholly owned subsidiary of Covestro AG, a publicly traded company.
Covestro AG owns more than 10% of Covestro LLC.
ADNOC International Germany Holding AG owns
more than 10% of the stock of Covestro AG. ADNOC
International Germany Holding AG is a wholly owned
subsidiary of ADNOC International UK Limited,
which is a wholly owned subsidiary of XRG P.J.S.C.,
which is a wholly owned subsidiary of Abu Dhabi National Oil Company (ADNOC) P.J.S.C.
iv
RELATED PROCEEDINGS
The proceedings directly related to this petition
are:
•
Sommerville v. Union Carbide Corporation;
Covestro LLC, No. 24-1491 (4th Cir. Aug. 18,
2025)
•
Sommerville v. Union Carbide Corporation,
No. 2:19-cv-00878 (S.D. W. Va. March 20,
2024)
•
Sommerville v. Union Carbide Corporation,
No. 2:19-cv-00878 (S.D. W. Va. May 13, 2024)
v
TABLE OF CONTENTS
Page
QUESTION PRESENTED ........................................... i
PARTIES TO THE PROCEEDINGS .......................... ii
RULE 29.6 STATEMENT ..........................................iii
RELATED PROCEEDINGS....................................... iv
TABLE OF CONTENTS.............................................. v
TABLE OF AUTHORITIES ...................................... vii
OPINIONS BELOW .................................................... 1
JURISDICTION........................................................... 1
PROVISIONS INVOLVED.......................................... 1
INTRODUCTION ........................................................ 1
STATEMENT OF CASE ............................................. 4
REASONS FOR GRANTING THE PETITION ........ 12
I.
The Courts of Appeals Are Divided Over
Whether Challenges to the Factual
Basis of an Expert’s Opinion Always Go
to Weight, Not Admissibility .......................... 12
II.
The Fourth Circuit’s Decision Is
Incorrect .......................................................... 21
III.
The Question Presented Is Exceptionally
Important and Warrants Review in This
Case ................................................................. 25
A.
Resolution of the Question
Presented Is of Overriding
Importance............................................ 25
B.
This Case Is an Ideal Vehicle .............. 30
vi
TABLE OF CONTENTS
(continued)
Page
CONCLUSION .......................................................... 32
APPENDICES
Appendix A: Opinion of the United States
Court of Appeals for the Fourth Circuit
(August 18, 2025) ...................................................... 1a
Appendix B: Opinion of the United States
District Court for the Southern District of
West Virginia (March 20, 2024) ............................. 42a
Appendix C: Opinion of the United States
District Court for the Southern District of
West Virginia (May 13, 2024)................................. 89a
Appendix D: Order of the United States
Court of Appeals for the Fourth Circuit
Denying Rehearing (November 4, 2025) .............. 116a
Appendix E: Provisions Involved ........................ 117a
vii
TABLE OF AUTHORITIES
Page(s)
FEDERAL CASES
Baker v. Blackhawk Mining,
141 F.4th 760 (6th Cir. 2025) ......................... 16, 19
Bliv v. Charter Oak Fire Ins.,
159 F.4th 539 (8th Cir. 2025) ............................... 18
Bresler v. Wilmington Trust,
855 F.3d 178 (4th Cir. 2017) ................. 2, 3, 10, 11,
.............................................................. 18, 22-24, 29
In re Camp Lejeune Water Litig.,
2025 WL 3565850 (E.D.N.C. Dec. 12,
2025)...................................................................... 29
Clark v. Martinez,
543 U.S. 371 (2005) .............................................. 23
Daubert v. Merrell Dow
Pharmaceuticals,
509 U.S. 579 (1993) ................. 2, 4, 5, 21-24, 26, 30
Doucette v. Jacobs,
106 F.4th 156 (1st Cir. 2024) ........................... 4, 21
EcoFactor v. Google,
137 F.4th 1333 (Fed. Cir. 2025) .... 6, 13, 16, 17, 20
Engilis v. Monsanto,
151 F.4th 1040 (9th Cir. 2025) ........... 14, 15, 19, 20
Gen. Elec. v. Joiner,
522 U.S. 136 (1997) ........................................ 11, 26
viii
TABLE OF AUTHORITIES
(continued)
Page(s)
Harris v. FedEx Corp. Servs.,
92 F.4th 286 (5th Cir. 2024) ........................... 17, 19
Kumho Tire v. Carmichael,
526 U.S. 137 (1999) .................................... 1, 26, 27
Michael’s Fabrics v. Donegal Mut. Ins.,
2025 WL 2624280 (D. Md. Sept. 11,
2025)...................................................................... 28
Milward v. Acuity Specialty Products
Group,
639 F.3d 11 (1st Cir. 2011) ....................... 20, 21, 24
Mincey v. Se. Farm Equip.,
2025 WL 2450913 (D.S.C. Aug. 26,
2025)...................................................................... 29
Nairne v. Landry,
151 F.4th 666 (5th Cir. 2025) ......................... 17, 19
In re Onglyza (Saxagliptin) &
Kombiglyze (Saxagliptin &
Metformin) Products Liability
Litigation,
93 F.4th 339 (6th Cir. 2024) ........................... 15, 19
Rodriguez v. Hosp. San Cristobal,
91 F.4th 59 (1st Cir. 2024) ............................... 4, 21
Sprafka v. Medical Device Business
Services,
139 F.4th 656 (8th Cir. 2025) ......................... 17, 18
ix
TABLE OF AUTHORITIES
(continued)
Page(s)
Tome v. United States,
513 U.S. 150 (1995) ................................................ 5
STATE CASE
Bower v. Westinghouse Elec.,
522 S.E.2d 424 (W. Va. 1999)............................. 7, 9
FEDERAL STATUTE
28 U.S.C. 1254(1) ......................................................... 1
FEDERAL RULES
Fed. R. Evid. 104(a) ....................................... 4, 5, 6, 13
Fed. R. Evid. 702....................... 1, 2-6, 11, 13-24, 27-31
Fed. R. Evid. 702(a) ............................................. 4, 5, 6
Fed. R. Evid. 702(b) .......... 2, 4-6, 11, 21, 22, 24, 29, 31
Fed. R. Evid. 702(c) ........................................ 4, 5, 6, 22
Fed. R. Evid. 702(d) ............................................. 4, 5, 6
OTHER AUTHORITIES
Margaret A. Berger, The Admissibility
of Expert Testimony, in Federal
Judicial Center, Reference Manual
on Scientific Evidence (3d ed. 2011) .................... 27
x
TABLE OF AUTHORITIES
(continued)
Page(s)
Stephen G. Breyer, Introduction, in
Federal Judicial Center, Reference
Manual on Scientific Evidence (3d
ed. 2011) ................................................................ 26
Federal Rules of Evidence–Expert
Testimony–Judicial Conference
Amends Rule 702–Federal Rule of
Evidence 702,
138 Harv. L. Rev. 899 (2025) ....... 13, 20, 29, 30, 31
Peter Huber, Junk Science and the Jury,
1990 U. Chi. Legal F. 273 (1990) ................... 23, 27
Lee Mickus, Amended Rule 702 in 2025,
Wash. Legal Found. (Oct. 7, 2025),
https://www.wlf.org/2025/10/07/
publishing/amended-rule-702-in2025-circuit-courts-embrace-thechanged-standard/ ................................................ 29
Christopher R.J. Pace, Admitting and
Excluding General Expert Testimony:
The Eleventh Circuit Construct,
37 Am. J. Trial Advoc. 47 (2013).......................... 27
Jed S. Rakoff, Science and the Law:
Uncomfortable Bedfellows,
38 Seton Hall L. Rev. 1379 (2008) ....................... 26
xi
TABLE OF AUTHORITIES
(continued)
Page(s)
Thomas D. Schroeder, Toward A More
Apparent Approach to Considering
the Admission of Expert Testimony,
95 Notre Dame L. Rev. 2039 (2020) ............... 24, 29
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) .............................. 26
1
Petitioners respectfully petition for a writ of certiorari to review the judgment of the U.S. Court of Appeals for the Fourth Circuit.
OPINIONS BELOW
The opinion of the court of appeals (App., infra, at
1a) is reported at 149 F.4th 408. The order denying
rehearing en banc (App., infra, at 116a) is unpublished. The district court’s order excluding expert
testimony (App., infra, at 42a) is available at 2024 WL
1204094. The district court’s order dismissing the case
(App., infra, at 89a) is available at 2024 WL 2139394.
JURISDICTION
The judgment of the court of appeals was entered
on August 18, 2025. App., infra, at 1a. A timely petition for rehearing en banc was denied on November 4,
2025. Id. at 116a. This Court’s jurisdiction is invoked
under 28 U.S.C. 1254(1).
PROVISIONS INVOLVED
The relevant provisions are reproduced in the appendix to this petition. App., infra, at 117a.
INTRODUCTION
Federal Rule of Evidence 702 imposes an obligation
on federal district judges to ensure that expert testimony meets threshold criteria of reliability before juries may consider that evidence. Faithful discharge of
that obligation is essential. “[E]xpertise that is fausse
and science that is junky” threaten the credibility of
the adjudicatory process. Kumho Tire v. Carmichael,
526 U.S. 137, 158-159 (1999) (Scalia, J., concurring).
Jurors seldom possess the knowledge and experience
necessary to assess the scientific and technical expert
testimony that has come to play such an outsized role
in complex civil litigation. At the same time, jurors
2
are prone to give considerable deference to such expert
testimony. See Daubert v. Merrell Dow Pharmaceuticals, 509 U.S. 579, 595 (1993).
Rule 702’s requirement that “the [expert’s] testimony is based on sufficient facts or data” addresses
those very risks. Fed. R. Evid. 702(b). For years after
this Court’s decision in Daubert, many courts of appeals held that district courts applying this criterion
must determine by a preponderance of the evidence
that sufficient facts or data support an expert’s opinion to render it reliable enough for the jury to consider.
But courts like the First and Fourth Circuits applied
a different rule. Those circuits held that doubts about
the factual underpinnings of an expert’s opinion categorically go to the weight jurors should give to that evidence, not to the threshold question of its admissibility. Needless to say, that approach materially increased the risks that jury verdicts will be the product
of junk science or other misconceived faux expertise.
In 2023, Rule 702 was amended for the express
purpose of repudiating the approach of the First and
Fourth Circuits and clarifying that district courts
should not admit expert testimony unless they first determine by a preponderance of the evidence that an
expert’s opinion is based on sufficient facts and data to
establish its reliability. Judge Schroeder, the Chair of
the Subcommittee that drafted the amendments, specifically pointed to the Fourth Circuit’s decision in
Bresler v. Wilmington Trust, 855 F.3d 178, 195 (4th
Cir. 2017)—which held that questions about an expert’s “factual underpinnings” do not “affect * * * admissibility”—as an exemplar of the error the amendment was trying to correct.
Unfortunately, the Fourth Circuit did not get the
message. In the decision below, a sharply divided
3
panel held that the district court had abused its discretion when it concluded that plaintiff’s proposed expert had not established by a preponderance of the evidence that the factual underpinnings of his analysis
were sufficiently reliable to justify admission of the
testimony.
This case—a putative class action in which the
plaintiff alleges a medical-monitoring claim based on
allegations that the plaintiff breathed in a contaminant allegedly generated by defendants’ operations—
is precisely the kind of case in which faithful application of Rule 702 is particularly important. The plaintiff’s proposed expert attempted to demonstrate community exposure to the contaminant by extrapolating
data from a single year over a 36-year period, using
data relating to a facility that has nothing to do with
plaintiff’s lawsuit, relying on projected emissions for a
single year that were inexplicably more than 100
times greater than for any other year, and using multiple contradictory sets of weather information from
non-representative locations.
Expressly relying on Bresler, one of the very decisions taking the approach that the Advisory Committee repudiated, the court of appeals held that the inadequacy of the factual basis for the expert’s testimony
was a matter for the jury to consider in deciding how
much weight to give that testimony—not a reason to
refuse to admit the evidence in the first place. As
Chief Judge Diaz observed in dissent, the court’s ruling is irreconcilable with Rule 702 and the rule that
most circuits apply. App., infra, at 35a (“an expert
who constructs a model based on faulty assumptions
and irrelevant data shouldn’t be handed a ‘get-out-ofDaubert-free card,’” regardless of whether “he uses an
otherwise reliable modeling system”).
4
At this point, it is clear that the 2023 amendments
have failed to bring the Fourth Circuit into alignment
with the correct understanding of Rule 702 that most
circuits apply. And the First Circuit has taken the
same obdurate approach as the Fourth Circuit. 1 Given
how frequently the question arises and how serious
the consequences of mistaken admission of expert scientific testimony can be in a wide variety of cases, including putative tort class actions like this one, this
Court’s immediate intervention is urgently needed.
STATEMENT OF CASE
1. Federal Rule of Evidence 702 states that an expert witness “may testify in the form of an opinion”
only “if the proponent demonstrates to the [district]
court that it is more likely than not” that several reliability-related requirements are satisfied. Fed. R.
Evid. 702; see Fed. R. Evid. 104(a). The proponent
must persuade the court that “the [expert’s] testimony
is based on sufficient facts or data.” Fed. R. Evid.
702(b). The proponent also must persuade the court
that “the expert’s scientific, technical, or other specialized knowledge will help the trier of fact to understand
the evidence or to determine a fact in issue”; “the testimony is the product of reliable principles and methods”; and “the expert’s opinion reflects a reliable application of the principles and methods to the facts of the
case.” Fed. R. Evid. 702(a), (c)-(d).
The current version of Rule 702 is the product of
two sets of amendments that occurred after this
Court’s landmark decision in Daubert v. Merrell Dow
See Rodriguez v. Hosp. San Cristobal, 91 F.4th 59, 70 (1st Cir.
2024) (applying rule from decision that Judge Schroeder identified as emblematic of the incorrect approach); Doucette v. Jacobs,
106 F.4th 156, 169 (1st Cir. 2024) (same).
1
5
Pharmaceuticals, 509 U.S. 579 (1993). Daubert requires trial courts to take on a “gatekeeping role” to
“ensure that any and all scientific testimony or evidence admitted is not only relevant, but reliable.” Id.
at 589, 597.
In 2000, Rule 702 was amended to “affirm[] the
trial court’s role as gatekeeper.” Fed. R. Evid. 702 advisory committee’s notes to 2000 amendments. 2 The
2000 amendments added reliability requirements now
found in Rule 702(a)-(d), including the requirement in
Rule 702(b) that an expert’s testimony be based on sufficient facts or data. Ibid. At the time, Rule 702 did
not expressly state that the proponent of evidence
must demonstrate to the district court by a preponderance of the evidence that those requirements are satisfied. But the Advisory Committee Notes to the 2000
amendments explained that Rule 104(a) separately required that more-likely-than-not showing.
Rule
104(a) governs the “admissibility of all expert testimony” and gives the “proponent” of such testimony
“the burden of establishing that the pertinent admissibility requirements are met by a preponderance of
the evidence.” Ibid.; see Fed. R. Evid. 104(a) (“The
court must decide any preliminary question about
whether a witness is qualified, a privilege exists, or evidence is admissible.”).
In 2023, Rule 702 was amended again to “clarify
and emphasize that expert testimony may not be admitted unless the proponent demonstrates to the court
This Court has long “relied on th[e] well-considered [Advisory
Committee] Notes as a useful guide in ascertaining the meaning
of the Rules” of Evidence. Tome v. United States, 513 U.S. 150,
160 (1995).
2
6
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. The amendments added
the phrase “the proponent demonstrates to the court
that it is more likely than not that” before the list of
reliability criteria in Rule 702(a)-(d). Ibid. The Advisory Committee explained that “many courts have
held that the critical question[] of the sufficiency of an
expert’s basis” is a “question[] of weight and not admissibility”—and that those holdings “are an incorrect
application of Rules 702 and 104(a)” that “made [it]
necessary” to “emphasiz[e] the preponderance standard in Rule 702” itself. Ibid.; see ibid. (criticizing court
rulings that “arguments about the sufficiency of an expert’s basis always go to weight and not admissibility”).
The 2023 amendments did not change the substantive or procedural requirements imposed by Rule 702.
“Rather, the amendment is simply intended to clarify
that Rule 104(a)’s requirement applies to expert opinions under Rule 702.” Fed. R. Evid. 702 advisory committee’s notes to 2023 amendments; accord EcoFactor
v. Google, 137 F.4th 1333, 1339 n.8 (Fed. Cir. 2025) (en
banc) (“The 2023 amendment did not substantively
change the relevant standard.”).
2. In this putative class action, respondent Lee
Ann Sommerville sued petitioners as operators of two
separate manufacturing facilities located in South
Charleston, West Virginia (collectively, “the Plant”).
App., infra, at 1a-2a. Respondent, who did not work
at or have any special connection to the Plant, asserted
a single claim for medical monitoring under West Virginia common law. She alleged that Plant operations
between 1984 and 2019 emitted ethylene oxide (“EtO”)
7
into the atmosphere, that she breathed in the EtO in
the course of her daily life, and that she faced an increased risk of future harm as a result. Ibid.
Respondent acknowledged that she could not establish liability without admissible expert testimony
showing that she had significant exposure to a “proven
hazardous substance” and that her exposure was
greater than that of the population at large. App., infra, at 19a (quoting Bower v. Westinghouse Elec., 522
S.E.2d 424, 432-433 (W. Va. 1999)). In an effort to
meet that requirement, respondent offered Dr. Ranajit
Sahu as an expert on petitioners’ EtO emissions during the relevant period, including where emissions
traveled geographically, and the “potential exposure
levels of [respondent] and the proposed class members.” Ibid.
Dr. Sahu claimed that he could model EtO emissions and determine an individual’s cumulative EtO
exposure based on a residential address and information about the years the individual lived there.
App., infra, at 33a. But to run the model, he first “had
to select the inputs” that the model would use, which
“included source data, receptor data, and meteorological data.” Id. at 19a. Dr. Sahu conceded that the “accuracy of the model bears a strong positive relationship to the correct inputs being used * * * that represent the actual condition” of the Plant and “its emissions sources.” Id. at 35a.
Dr. Sahu submitted an expert report setting forth
his methodology and findings. App., infra, at 44a. The
report explained that he did not try to assess emissions from the Plant alone—instead, he commingled
“results from both” the Plant and Union Carbide’s separate facility in Institute, West Virginia, even though
that separate facility is not at issue in this case. Id. at
8
44a, 56a. He also listed the emissions sources, emissions data, meteorological data, and data regarding
background levels of EtO that he inputted into his
model. Id. at 45a-49a, 61a-62a. Relying on those inputs, he opined that “persons in the surrounding community were exposed to significant concentrations of
EtO.” Id. at 48a.
3. a. After discovery closed, the district court
granted petitioners’ motions to exclude Dr. Sahu’s testimony. App., infra, at 42a-88a. The court first rejected respondent’s “contention that the instant motions raise questions affecting the weight and credibility of Dr. Sahu’s opinions rather than their admissibility.” Id. at 54a. The court explained that, “[u]pon detailed review of the expert reports, I find that the opinions of Dr. Sahu are not based upon sufficient facts or
data because the inputs he uses in the air model are
speculative and are premised on assumptions that do
not accurately represent [petitioners’] operations.” Id.
at 42a.
The district court identified a number of independent “substantive issues” that cast serious doubt on the
“reliability” of the data that Dr. Sahu used and rendered his testimony inadmissible. App., infra, at 60a.
For instance, Dr. Sahu treated data from a single year
as representative of emissions levels over the entire
36-year period from 1984 to 2019, without any justification for such an assumption and in the face of official
warnings that the data should not be used that way.
Id. at 62a-63a, 67a-75a. He did the same thing with
the “meteorological data” that he used to assess “emissions dispersion characteristics,” while also using
“three different, contradictory sets of meteorological
data taken from different locations” that were not
“representative” of the Plant. Id. at 76a-78a; see id. at
9
62a (explaining that Dr. Sahu relied on data relating
to both the Plant and the separate Union Carbide facility in Institute, even though the latter has nothing
to do with respondent’s suit). And he used emissions
estimates that resulted in projections of “EtO concentrations for the year 1984” that are inexplicably “‘over
100 times greater’ than the estimates for some of the
other years in the potential class period,” without validating his data or adequately explaining the disparity. Id. at 70a.
b. In May 2024, the district court granted petitioners’ motion for summary judgment. App., infra, at
89a-115a. The court explained that respondent “relie[d] entirely” on the expert “to prove her alleged increased risk of cancer development due to the alleged
EtO emissions.” Id. at 104a. But the court had already “excluded * * * Dr. Sahu, because he used patently unreliable data and methods in creating the air
model used to determine the alleged estimated EtO
emissions—and therefore the increased risk of disease.” Id. at 104a-105a. Accordingly, the court concluded, respondent could not establish any injury and
lacked standing to proceed.
4. The Fourth Circuit reversed in a divided opinion. App., infra, at 1a-41a. While agreeing that respondent can pursue her medical-monitoring claim
only if she “put[s] forth admissible expert testimony to
establish” that “she was * * * ‘significantly exposed’
to a proven hazardous substance,” the majority (Ben-
10
jamin, J.) ruled that the district court abused its discretion in excluding Dr. Sahu’s expert testimony. Id.
at 18a-21a (quoting Bower, 522 S.E.2d at 432-433). 3
The majority identified the district court’s error as
“[e]xcluding Dr. Sahu” for his “choice of source [data]
and meteorological data.” App., infra, at 20a. That
was wrong, the majority held, because “questions regarding the factual underpinnings of the [expert witness’] opinion affect the weight and credibility of the
witness’ assessment, not its admissibility.” Id. at 20a21a (citation omitted). In a footnote, the majority purported to acknowledge that “a district court can decide
that an expert’s opinion lacks sufficient support in the
record.” Id. at 27a n.7 (citation omitted). But in the
same breath, the majority reemphasized that a court
cannot exclude expert testimony based on “disagreement with an expert’s choice of data” or “its own assessment of the correctness of an expert’s opinions,”
and quoted Bresler v. Wilmington Trust, 855 F.3d 178,
195 (4th Cir. 2017), for the unqualified proposition
that questions about an expert’s “factual underpinnings” do not “affect * * * admissibility.” Ibid. (emphasis omitted).
The majority repeatedly relied on that principle of
law, referring to Bresler multiple times throughout its
opinion. E.g., App., infra, at 21a, 22a, 27a. For example, the court of appeals deemed the district court’s critique of Dr. Sahu’s “choice of meteorological inputs”
improper on the ground that the court “conflated admissibility with the weight a factfinder might attribute Dr. Sahu’s testimony based on his choice of data.”
The majority also concluded that respondent has Article III
standing because of her alleged “need” to pay “for medical testing
today to mitigate an increased risk of illness.” App., infra, at 16a.
3
11
Id. at 24a-25a. The court of appeals said the same
thing about the district court’s analysis of Dr. Sahu’s
“choice of source parameters” and “emissions data selections,” deeming that analysis a “violat[ion of] Bresler’s holding that ‘questions regarding the factual underpinnings of the [expert witness’] opinion” go only to
“weight and credibility,” not “admissibility.’” Id. at
20a-22a (quoting 855 F.3d at 195). And the court of
appeals ruled that “[e]xcluding Dr. Sahu for failing to
‘validate’ his data” impermissibly rested on “disagree[ment] with Dr. Sahu’s choice of data,” which
Bresler “forbids.” Id. at 21a-22a (citing 855 F.3d at
196).
In dissent, Chief Judge Diaz explained why the district court “correctly excluded” Dr. Sahu’s testimony
and, at minimum, did not abuse its discretion. App.,
infra, at 33a. He emphasized that the majority was
mistaken in holding that district courts may not consider questions about the factual underpinnings of an
expert’s testimony in deciding admissibility. Id. at 36a
(citing Fed. R. Evid. 702(b), and Gen. Elec. v. Joiner,
522 U.S. 136, 146 (1997)).
Under the proper Rule 702 standard, Chief Judge
Diaz reasoned, it is clear that Dr. Sahu’s testimony
“wasn’t well-grounded in the facts and data available”
and that the district court “had good reason to be concerned about Dr. Sahu’s failure to justify the assumptions he made in creating the inputs for the dispersion
model.” App., infra, at 34a, 37a; see id. at 35a (“an
expert who constructs a model based on faulty assumptions and irrelevant data shouldn’t be handed a
‘get-out-of-Daubert-free card,’” regardless of whether
“he uses an otherwise reliable modeling system”). For
instance, Chief Judge Diaz explained, Dr. Sahu “relied
12
on values that expressly didn’t represent actual emissions”; “ignored telltale signs that there might be a
problem with the emissions values he used”; “combined meteorological data from three locations,” including locations “some distance away” from the Plant;
and “held a value (e.g., emissions, operations) from one
year constant over several years (or, for the meteorological data, for the entire thirty-year period at issue)”
without explaining how doing so could possibly make
sense. Id. at 38a-39a.
In Chief Judge Diaz’s view, those type of “concerns”
fall “squarely within the district court’s purview” because they are an important part of fulfilling its “gatekeeping responsibility.” App., infra, at 34a-37a. Because he would have upheld the exclusion of the expert’s testimony, he also would have affirmed the district court’s grant of summary judgment to petitioners
on the ground that respondent failed to “meet her burden * * * to demonstrate an injury in fact.” Id. at
33a. 4
REASONS FOR GRANTING THE PETITION
I.
The Courts of Appeals Are Divided Over
Whether Challenges to the Factual Basis
of an Expert’s Opinion Always Go to
Weight, Not Admissibility
The Fourth Circuit’s decision in this case entrenched a conflict between the First and Fourth Circuits on one side and the Fifth, Sixth, Eighth, Ninth,
and Federal Circuits on the other. Circuits in the for-
Chief Judge Diaz also would have held that “medical monitoring
costs (incurred or anticipated), without more, can’t confer standing to seek damages in federal court.” App., infra, at 30a.
4
13
mer category hold—in the words of the decision below—that challenges to the factual basis of an expert’s
testimony “affect the weight and credibility” of an expert’s testimony and “not its admissibility,” App., infra, at 20a-21a, while circuits in the latter category
hold that such challenges go to the weight of the evidence only if a court first finds it more likely than not
that an expert’s testimony has a sufficient factual basis to render it reliable.
A. That split has been brewing for a number of
years—but recent developments make it intolerable.
In 2023, Rule 702 was amended to address the decisions of “courts” that had “incorrect[ly]” “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. That amendment was intended to “clarify,” not
to change, the existing requirements of the Rules of
Evidence. Ibid.; see EcoFactor v. Google, 137 F.4th
1333, 1339 n.8 (Fed. Cir. 2025) (en banc) (“The 2023
amendment did not substantively change the relevant
standard.”). It did so by adding an express reference
in Rule 702 to the separate requirement in Rule 104(a)
that the proponent of evidence establish admissibility
by a preponderance of the evidence. See Fed. R. Evid.
104(a). As of December 1, 2023, therefore, the
amended Rule 702 provides that expert testimony is
admissible “if the proponent demonstrates to the court
that it is more likely than not that * * * the testimony
is based on sufficient facts or data.” Fed. R. Evid. 702
(emphasis added).
After that amendment, courts of appeals that had
previously required district courts to determine that
expert testimony more likely than not has a sufficient
factual basis before admitting it continued to enforce
14
that requirement. And some courts of appeals that
had not consistently approached admissibility that
way fell into line. But two courts of appeals—the
Fourth Circuit, which issued the decision below, and
the First Circuit—continued to hold fast to their position that questions about an expert’s factual basis go
only to the weight of the expert’s testimony and therefore must be decided by a jury. See Federal Rules of
Evidence—Expert Testimony—Judicial Conference
Amends Rule 702—Federal Rule of Evidence 702, 138
Harv. L. Rev. 899, 903 (2025).
Thus, despite the amendments to Rule 702, there
remains an intractable circuit split over whether a district court must determine whether it is more likely
than not that an expert has a sufficient factual basis
to support an opinion before allowing that opinion to
be admitted as evidence.
B. The Fifth, Sixth, Eighth, Ninth, and Federal
Circuits have hewed to the approach prescribed in the
Rule 702 advisory committee notes.
The Ninth Circuit’s decision in Engilis v. Monsanto, 151 F.4th 1040 (9th Cir. 2025), is illustrative.
That decision traces Rule 702’s history, including the
clarifying 2023 amendments, and holds that,
“[p]roperly applied, Rule 702 requires 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.”
Id. at 1049 (emphasis added); see id. at 1051 (explaining that Rule 702 requires district courts “to screen expert testimony” to ensure, among other things, that it
is “‘based on sufficient facts or data’” (quoting Fed. R.
15
Evid. 702(b))). 5 Applying the more-likely-than-not test
reaffirmed in the 2023 amendments, the court of appeals upheld the district court’s decision to exclude the
expert testimony because the expert had insufficient
facts to conclude that the plaintiff was not obese,
which was a key premise of the expert’s opinion on the
causes of a medical condition. See ibid. The court of
appeals recognized that some evidence—a medical
“fact sheet” stating that the plaintiff was “negative” for
obesity—supported the expert’s premise, but nonetheless upheld the district court’s conclusion that the
plaintiff had not shown a sufficient factual basis by a
“preponderance of the evidence.” Id. at 1051-1052.
The other circuits’ decisions are of a piece. In In re
Onglyza (Saxagliptin) & Kombiglyze (Saxagliptin &
Metformin) Products Liability Litigation, 93 F.4th 339
(6th Cir. 2024), the Sixth Circuit affirmed the district
court’s exclusion of an expert’s testimony, holding
that, “[b]efore admitting expert testimony, the district
court needed to ensure that” the expert’s testimony
was “‘based on sufficient facts or data.’” 93 F.4th at
345 (quoting Fed. R. Evid. 702); see id. at 348 (“competing expert opinions present the classic battle of the
experts and it is up to a jury to evaluate what weight
and credibility each expert opinion deserves,” but “district courts may allow juries to evaluate and weigh
only relevant and reliable expert testimony” (citation
omitted)). The Sixth Circuit noted the clarifying 2023
amendments but explained that its decision “would be
the same under either version of the Rule.” Id. at 345
n.4. The court of appeals concluded that the district
court had not abused its discretion in finding that the
The Ninth Circuit noted that the applicable “version of the Rule”
did not make a difference, consistent with the fact that the 2023
amendments were merely clarifying. 151 F.4th at 1049 n.9.
5
16
expert’s testimony lacked sufficient factual support, as
his attempt to link defendants’ diabetes drug to patients’ heart failure relied on a single trial but set
aside “without an adequate explanation” subsequent
studies reaching the opposite conclusion. Id. at 346.
Notably, the court of appeals upheld the exclusion of
the testimony even though the expert had made some
effort to explain away the later studies, because the
preponderance of the evidence did not establish a sufficient basis for the expert’s opinion. Id. at 345.
The Sixth Circuit later applied the same rule in
Baker v. Blackhawk Mining, 141 F.4th 760 (6th Cir.
2025), which is factually similar to this case. The
Sixth Circuit held that the district court had not erred
in concluding that a causation expert’s report was “not
based upon sufficient facts or data” about the “specific
mining sites” that supposedly caused the plaintiffs’ injury, rendering it unreliable under Rule 702. Id. at
770 (citation omitted). The court of appeals was not
swayed by the fact that the expert looked to studies
about other mining sites nearby; that was not enough
to send the case to a jury to decide how heavily to
weigh the expert’s testimony. See id. at 763-765, 770.
The law is the same in the Federal Circuit. Most
recently, in EcoFactor v. Google, 137 F.4th 1333 (Fed.
Cir. 2025) (en banc), the en banc court concluded that
a lack of support for an expert’s damages opinion
meant that the expert’s testimony should have been
excluded, as there was not “a sufficient factual basis
for [the expert] to provide a reliable opinion” on an estimated reasonable royalty. Id. at 1344. The Federal
Circuit explained that it was not “usurp[ing] the province of the jury”; it was simply exercising “the gatekeeping function of the court to ensure that there are
17
sufficient facts or data” for the expert’s opinion, consistent with the 2023 amendments clarifying Rule 702.
Id. at 1339, 1343; see id. at 1339-1340 (noting the advisory committee’s statement that it is incorrect to
hold that “the critical question[] of the sufficiency of an
expert’s basis” is a “question[] of weight and not admissibility” and emphasizing that “[d]istinguishing
‘the gatekeeping role of the judge’ * * * from the fact
finder’s role” is “essential” (citation omitted)). Again,
the court reached that conclusion even though there
was some factual basis for the expert’s opinion, see id.
at 1343—because the evidence on which the expert relied did not satisfy Rule 702’s “more likely than not”
standard. Id. at 1341-1342, 1344-1346.
The Fifth Circuit similarly recognizes that Rule
702 requires district courts to evaluate whether an expert’s data is sufficiently sound before a jury may consider it. For example, in Nairne v. Landry, 151 F.4th
666 (5th Cir. 2025), the court of appeals affirmed a district court’s exclusion of an expert on the ground that
his testimony regarding voting patterns was not
“based on sufficient data,” as the expert had considered only some elections and inexplicably excluded
others. Id. at 698. In doing so, the Fifth Circuit cited
the 2023 amendments, on which the district court had
relied. See id. at 697-698; see also, e.g., Harris v.
FedEx Corp. Servs., 92 F.4th 286, 303-304 (5th Cir.
2024) (reversing a district court’s refusal to exclude expert testimony because the court “abdicated its role as
gatekeeper” by admitting testimony that was not
“based on sufficient facts or data”).
Finally, in Sprafka v. Medical Device Business Services, 139 F.4th 656 (8th Cir. 2025), the Eighth Circuit
applied the same rule in a design-defect case. See id.
at 661. “After Rule 702’s recent amendment,” the
18
Eighth Circuit stated, “courts continue to have a gatekeeping role” to “discern expert opinion evidence based
on ‘good grounds’ from subjective speculation.” Ibid.
(citation omitted). Applying that rule, the court of appeals concluded that the district court had not abused
its discretion in refusing to admit expert testimony
that a medical-device manufacturer was responsible
for a common side effect of a medical procedure that
the plaintiff had undergone. See id. at 659-661. That
conclusion was based on an examination of the expert’s factual basis, including the expert’s reliance on
only a few small studies and some anecdotal observations. Although those provided some basis for the expert’s opinion, that was not enough to justify putting
the expert’s testimony before a jury to determine its
weight. See id. at 661-662; see also, e.g., Bliv v. Charter Oak Fire Ins., 159 F.4th 539, 544 (8th Cir. 2025)
(affirming district court’s exclusion of expert testimony where there was “a reasoned basis to find” that
the expert “failed to consider or account for critical information when forming his opinions”).
C. The Fourth Circuit, along with the First Circuit,
applies a legal rule that is irreconcilable with the rule
applied by the circuits above. Despite the clear direction provided by the 2023 amendments to Rule 702,
those two circuits continue to treat questions about the
sufficiency of the factual basis for an expert’s testimony as going only to the weight of that evidence—
and thus, invariably, as a jury question rather than as
a threshold admissibility question that courts must
decide.
1. In the decision below, the Fourth Circuit categorically held that “‘questions regarding the factual
underpinnings of [an expert’s] opinion affect the
weight and credibility of the witness’ assessment, not
19
its admissibility.’” App., infra, at 20a-21a (quoting
Bresler v. Wilmington Tr. Co., 855 F.3d 178, 195 (4th
Cir. 2017)). On that basis, the court of appeals rejected
the district court’s many criticisms of the data on
which the expert relied—which included air-quality
data from locations and time periods that are not at
issue in this case—and ruled that the expert’s testimony was admissible. See id. at 20a-27a. But the
court of appeals did not determine whether it was
more likely than not that the expert’s testimony was
supported by sufficient facts or data. See ibid. The
court below thus took exactly the approach that the
advisory committee notes to the 2023 amendments
roundly criticize and that the circuits on the other side
of the split have firmly rejected.
The specific reasoning that the Fourth Circuit employed highlights that split in authority. For example,
the Fourth Circuit ruled that the district court abused
its discretion in holding that the expert used “unreliable” data, stating that the expert “provided reasons for
why” he “believe[d]” the data was accurate that a jury
should “weigh[].” App., infra, at 22a. But the circuits
on the other side of the split have repeatedly recognized that the existence of some factual basis for expert testimony is not enough to satisfy Rule 702; rather, the question is whether the preponderance of the
evidence establishes the likelihood that a sufficient basis exists. See, e.g., Engilis, 151 F.4th at 1050-1051
(Ninth Circuit deeming expert testimony inadmissible
for lack of sufficient factual basis even though expert
had a medical “fact sheet” supporting his factual assertion); Onglyza, 93 F.4th at 345 (Sixth Circuit deeming expert testimony inadmissible for lack of sufficient
factual basis even though the expert “provided reasons” for relying on one clinical trial and discounting
20
others). The decision below is peppered with such conflicts in reasoning, driven by the stark differences between the circuits’ legal rules. 6
2. The First Circuit has long taken the same approach as the Fourth Circuit. See Judicial Conference
Amends Rule 702, 138 Harv. L. Rev. at 903 (“The First
Circuit provides an example of a court that has not
acknowledged the impact the amendments ought to
have had on its approach to Rule 702 inquiries.”).
Milward v. Acuity Specialty Products Group, 639
F.3d 11 (1st Cir. 2011), exemplifies the First Circuit’s
approach. There, the court of appeals held that the
district court’s “challenge[s] [to] the factual underpinnings of [the expert’s] opinion” that exposure to a
chemical substance caused cancer “overstepped the
authorized bounds of its role as gatekeeper” because
“[t]he soundness of the factual underpinnings of the
expert’s analysis” is a “factual matter[] to be determined by the trier of fact.” Id. at 22 (citation omitted).
In the First Circuit’s view, even if—as the district
court had concluded—“the factual underpinning of
[the] expert’s opinion is weak,” that weakness affects
Compare App., infra, at 20a-21a (stating that the expert’s
“choice of which data to input into his model” goes only to “weight
and credibility” and that whether expert failed to validate data is
not relevant to admissibility), with Nairne, 151 F.4th at 698 (expert testimony properly excluded where expert failed to include
relevant data in his model); Harris, 92 F.4th at 303 (same); Onglyza, 93 F.4th at 346 (same); Baker, 141 F.4th at 770 (expert testimony properly excluded where expert relied on improper data);
EcoFactor, 137 F.4th at 1344 (expert testimony properly excluded
where expert did not validate his data but rather relied on only a
fact witness’s unsupported say-so); Engilis, 151 F.4th at 1052 (expert testimony properly excluded where expert relied on data that
the expert failed to validate by “undertak[ing] any evaluation” of
the underlying facts).
6
21
only “the weight and credibility of the testimony” and
is therefore “a question to be resolved by the jury.”
Ibid. (citation omitted); see id. at 23 (“The questions
that the [district] court posed were sensible ones, but
ones for the jury to resolve.”). In deeming the expert’s
testimony admissible, the First Circuit—like the
Fourth Circuit in this case—never asked the critical
question on which the other circuits’ admissibility
analysis rests: whether the plaintiff had established
that it was more likely than not that the expert’s testimony was based on sufficient facts or data. See ibid.
And the First Circuit has repeatedly applied Milward’s rule even after the 2023 amendments to Rule
702. See Rodriguez v. Hosp. San Cristobal, 91 F.4th
59, 70 (1st Cir. 2024); Doucette v. Jacobs, 106 F.4th
156, 169 (1st Cir. 2024).
In short, there is no way to square the rule applied
by the court below and the First Circuit with the rule
applied by the Fifth, Sixth, Eighth, Ninth, and Federal
Circuits. Action by this Court is urgently needed to
bring uniformity to this important area of the law.
II.
The Fourth Circuit’s Decision Is Incorrect
A. The rule that the Fourth Circuit applied below
is at odds with the plain text of Rule 702. Rule 702
assigns to trial court judges “a gatekeeping role” to
“ensure that any and all scientific testimony or evidence admitted is not only relevant, but reliable.”
Daubert, 509 U.S. at 589, 597. The rule expressly provides that “[a] witness who is qualified as an expert
* * * 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 * * * the testimony is based
on sufficient facts or data” and that various other reliability requirements are satisfied. Fed. R. Evid.
702(b).
22
Accordingly, where a party challenges an expert’s
opinion as not “based on sufficient facts or data,” the
court must address such a challenge before it can admit the testimony. Fed. R. Evid. 702(b); see Daubert,
509 U.S. at 590. If the court concludes by a preponderance of the evidence that the testimony is not based
on sufficient facts or data—for example, because the
expert’s predicate facts are wrong, the expert failed to
account for important data, or the expert included irrelevant data—then the court must exclude the testimony. And if the court concludes by a preponderance
of the evidence that the expert’s testimony has a sufficient factual basis, then the court should admit the
testimony so that the jury can hear it and decide how
much weight to give it. That is the same preponderance-of-the-evidence test that courts apply when evaluating the other reliability factors listed in Rule 702,
such as whether “the testimony is the product of reliable principles and methods” and whether “the expert’s
opinion reflects a reliable application of the principles
and methods to the facts of the case.” Fed. R. Evid.
702(c)-(d); see generally Daubert, 509 U.S. at 592-593.
The Fourth Circuit’s approach is irreconcilable
with Rule 702 and with this Court’s explication of it.
The district court in this case excluded the expert’s testimony after identifying a host of reasons why his
opinion was not “based on sufficient facts or data.”
Fed. R. Evid. 702(b). Under Rule 702, reversal would
be appropriate only if the Fourth Circuit concluded
that respondent had “demonstrate[d] * * * that it is
more likely than not that” the expert’s report was
“based on sufficient facts or data.” Ibid. But the
Fourth Circuit never asked that question. To the contrary, it concluded that the district court abused its
discretion for having done so, holding that challenges
to the “factual underpinnings” of an expert’s testimony
23
are always for the jury, not the court, to resolve. App.,
infra, at 20a. And when the dissent challenged that
approach, the majority responded by quoting from the
Fourth Circuit’s earlier decision in Bresler v. Wilmington Trust, 855 F.3d 178 (4th Cir. 2017), articulating
the very same rule that the majority adopted: “questions regarding the factual underpinnings of the [expert witness’] opinion affect the weight and credibility
of the witness’ assessment, not its admissibility.” Id.
at 195 (citation omitted), quoted in App., infra, at 27a
n.7.
That approach is deeply problematic. It inexplicably treats one of the reliability factors in Rule 702—
whether “the testimony is based on sufficient facts or
data”—differently than the others, even though the
Rule uses exactly the same language as to each to describe how a court should conduct its admissibility
analysis. See Clark v. Martinez, 543 U.S. 371, 378
(2005) (“[t]o give these same [statutory] words a different meaning” when applied in different contexts
“would be to invent a statute rather than interpret
one”).
Even more to the point, that approach renders Rule
702’s intended “gatekeeping role” a nullity as to the
factual basis for expert testimony. Daubert, 509 U.S.
at 589, 597. The Fourth Circuit’s approach fails to
screen out expert testimony that lacks adequate rigor
because it is premised on insufficient facts or data, and
thereby creates exactly the risk that Rule 702 exists to
eliminate: that juries may well be swayed by such testimony because of the inherent force of any testimony
that is labeled “expert.” See, e.g., Peter Huber, Junk
Science and the Jury, 1990 U. Chi. Legal F. 273, 276277 (1990).
24
B. The 2023 amendments and accompanying Advisory Committee notes eliminate all doubt that the
decision below is fatally flawed. Those 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). As discussed, that
“clarif[ication]” was necessary because “many courts”
had “incorrect[ly]” “held that the critical question[] of
the sufficiency of an expert’s basis” is “always” a “question[] of weight and not admissibility.” Ibid. The Committee recognized that sometimes such questions could
go to the weight of evidence—but they could do so only
“once the court has found it more likely than not that
the admissibility requirement has been met.” Ibid.
There is no question that the Committee was referring to decisions like the one below. And to the extent
there were any doubt, Judge Schroeder, the Chair of
the Judicial Conference’s Subcommittee on Rule 702
that drafted the 2023 amendments, stated that the
amendments were directed at Bresler, the Fourth Circuit decision from 2017 that articulated the rule that
the court below applied to overturn the district court
in this case, and similar decisions. In cataloging decisions that “appear to be abdicating their charge under
the Federal Rules of Evidence and Daubert and its
progeny to make the hard call on admissibility,” Judge
Schroeder focused specifically on Bresler as “effectively vitiat[ing] the application of” the preponderance
test “to Rule 702(b).” Thomas D. Schroeder, Toward A
More Apparent Approach to Considering the Admission of Expert Testimony, 95 Notre Dame L. Rev. 2039,
2043, 2049-2050 (2020) (discussing Bresler’s holding
that “questions regarding the factual underpinnings”
25
affect “weight and credibility” and not “admissibility”);
see App., infra, at 21a-22a (repeatedly relying on and
quoting Bresler). And Judge Schroeder identified the
First Circuit’s opinion in Milward as “a prime example” of the same error. 95 Notre Dame L. Rev. at 2044.
C. Had the court of appeals properly applied Rule
702, it would have affirmed the district court’s exclusion of respondent’s expert—and that exclusion would
have ended the case, as it is indisputable that respondent’s claims cannot proceed without such expert testimony. See p. 7, supra. As Chief Judge Diaz’s dissent
explains, the district court’s many concerns with the
reliability of the expert’s data were not only well
grounded, but also “squarely within the district court’s
purview” in enforcing its “gatekeeping responsibility”—and the farthest thing from an abuse of discretion. App., infra, at 34a-37a (Diaz, C.J., dissenting). 7
III. The Question Presented Is Exceptionally
Important and Warrants Review in This
Case
A.
Resolution of the Question Presented Is
of Overriding Importance
1. Establishing that trial courts must determine
whether it is more likely than not that an expert’s testimony is supported by sufficient facts or data before
deeming that testimony admissible is a matter of
pressing importance. The issue recurs frequently. It
also is often outcome-determinative—or, at a minimum, powerfully influences how cases progress, what
In no event could the court of appeals properly have concluded
that the expert’s testimony was admissible without even considering whether it was more likely than not that the testimony had
a sufficient factual basis.
7
26
juries decide, and the parties’ incentives for settlement.
Expert testimony is of course ubiquitous in all
types of matters. It plays a particularly important role
in product-liability cases, patent cases, environmental
cases, and other cases in which science is central to
liability determinations. As jurists have observed,
“science in all its forms—hard science, soft science,
even so-called ‘junk’ science—has * * * invaded the
courtroom to an unparalleled extent.” Jed S. Rakoff,
Science and the Law: Uncomfortable Bedfellows, 38
Seton Hall L. Rev. 1379, 1379 (2008); see Stephen G.
Breyer, Introduction, in Federal Judicial Center, Reference Manual on Scientific Evidence 3 (3d ed. 2011)
(explaining that “[s]cientific issues” now “permeate
the law”); see also Joiner, 522 U.S. at 148-149 (Breyer,
J., concurring) (“modern life * * * depends upon the
use of artificial or manufactured substances,” making
it “particularly important * * * 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”).
Expert testimony also is likely to have an outsized
impact, especially when it addresses complex scientific
issues. Often, as here, a plaintiff’s case rests entirely
on expert testimony. See App., infra, at 40a (expert’s
“model is the only evidence that, for example, indicates
that [respondent] was exposed to EtO emitted by [petitioners’] operations”). And even when that is not
true, expert testimony is likely to have a major effect
on a factfinder’s determination. As this Court previously put it, “[e]xpert evidence can be both powerful
and quite misleading.” Daubert, 509 U.S. at 595 (citation omitted). “[E]xpertise that is fausse and science
27
that is junky” is a very real problem. Kumho Tire v.
Carmichael, 526 U.S. 137, 158-159 (1999) (Scalia, J.,
concurring); see 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, 224 (2006) (discussing “misleading junk science”).
The Rules “grant expert witnesses testimonial latitude
unavailable to other witnesses.” Kumho, 526 U.S. at
148-149. And expert “testimony often will rest upon
an experience confessedly foreign in kind to” a jury’s
“own,” ibid. (citation modified)—which means that jurors may well have difficulty, “due to lack of specialized knowledge,” in “evaluat[ing] meaningfully the reliability” of the expert’s data and methodology, Fed. R.
Evid. 702 advisory committee’s notes to 2023 amendments. Thus, even junk science, resting on purported
facts that are incorrect, misleadingly incomplete, or
simply irrelevant, may appear to jurors to “compellingly support[]” an “otherwise unsupportable claim.”
Huber, supra, 1990 U. Chi. Legal F. at 276-277.
Precisely because expert testimony can have such
a powerful effect, whether a court decides to admit an
expert’s testimony not only shapes the substantive decisions made within the litigation itself but also a defendant’s decision whether to settle. And when there
are serious doubts about the factual underpinnings of
an expert’s testimony but a court admits that testimony anyway on the ground that any such doubts go
only to the testimony’s weight, the defendant is often
pressured into a settlement to which it would not otherwise have agreed. See Margaret A. Berger, The Admissibility of Expert Testimony, in Federal Judicial
Center, Reference Manual on Scientific Evidence 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.”);
28
Rakoff, supra, at 1391 (noting that “shortly after” decision permitting plaintiffs to offer some expert testimony, “most of the 800 cases [in an MDL] settled”).
That problem is most acute in class actions and other
mass actions, where a court’s decision to admit the testimony of the plaintiffs’ expert often exerts “irresistible pressure” on a defendant “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.” Christopher R.J. Pace, Admitting
and Excluding General Expert Testimony: The Eleventh Circuit Construct, 37 Am. J. Trial Advoc. 47, 48
(2013).
2. The question presented arises with great frequency, as the many court of appeals decisions from
just the past few years demonstrate. See pp. 12-25,
supra. And scores of district-court decisions addressing that question never result in published appellate
decisions—often because an adverse ruling drives settlement.
In fact, the decision below has already influenced
district courts in the Fourth Circuit to admit expert
testimony without deciding whether it has a sufficient
factual basis, on the ground that any challenge to the
factual basis of an expert’s opinion goes only to weight
and therefore should be decided by a jury. For instance, immediately after the decision below, a Maryland district court invoked it to deny a motion to exclude a plaintiff’s expert testimony 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.” Michael’s
Fabrics v. Donegal Mut. Ins., 2025 WL 2624280, at *4
(D. Md. Sept. 11, 2025) (citation modified). District
29
courts in North Carolina and South Carolina have recently done the same. In re Camp Lejeune Water
Litig., 2025 WL 3565850, at *15 (E.D.N.C. Dec. 12,
2025); Mincey v. Se. Farm Equip., 2025 WL 2450913,
at *10 (D.S.C. Aug. 26, 2025).
3. At this point, it is clear that this Court’s intervention is necessary to ensure that the courts of appeals uniformly apply Rule 702 correctly.
The 2023 amendments to Rule 702 were intended
to “clarify and emphasize that expert testimony may
not be admitted unless the proponent demonstrates to
the court that it is more likely than not that the proffered testimony” is supported by sufficient facts or
data. Fed. R. Evid. 702 advisory committee’s notes to
2023 amendments. Many courts of appeals have taken
that clarification to heart. See pp. 14-18, supra. But
the court below and the First Circuit have defiantly
“doubl[ed] down on” their insistence that factual-basis
questions about expert testimony are not part of the
admissibility analysis—“a sign that the challenge of
achieving consistency is greater than something that
clarifying amendments can fix.” Judicial Conference
Amends Rule 702, 138 Harv. L. Rev. at 899; see Lee
Mickus, Amended Rule 702 in 2025, Wash. Legal
Found. (Oct. 7, 2025), https://www.wlf.org/2025/10/07/
publishing/amended-rule-702-in-2025-circuit-courtsembrace-the-changed-standard/.
The decision below exemplifies that troubling development. As noted, in the run-up to the 2023
amendments, Judge Schroeder specifically critiqued
the Fourth Circuit’s holding in Bresler that “questions
regarding the factual underpinnings of the [expert witness’] opinion affect the weight and credibility of the
witness’ assessment, not its admissibility,” explaining
30
that such an approach “effectively vitiated the application of [the preponderance test] to Rule 702(b).”
Schroeder, 95 Notre Dame L. Rev. at 2049-2050 (citation modified). Yet despite that criticism and the clarity of the 2023 amendments, the decision below continued to hew to Bresler’s erroneous holding, App., infra, at 20a-21a—and, in doing so, rebuffed the arguments in petitioners’ merits brief about the significance of those amendments, see Defendants-Appellees’ Br. 17, 19-20, 23 n.7 (4th Cir.). The Fourth Circuit then refused to grant rehearing en banc to revisit
that holding, even though it quite obviously conflicts
with the rule applied in multiple other circuits.
It is thus plain that this deep fissure in the law over
a critical aspect of Rule 702 will not close on its own.
There is only one way to ensure uniformity and correct
the misapplication of Rule 702: action by this Court.
The secondary literature has recognized as much—for
instance, 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” to the role that challenges
to an expert’s underlying facts or data play in the admissibility analysis. Judicial Conference Amends Rule
702, 138 Harv. L. Rev. at 906. That guidance is especially necessary given that the Court has not decided
on the merits any issue relating to Daubert in more
than 25 years.
B.
This Case Is an Ideal Vehicle
1. This case squarely presents the legal question
whether challenges to the factual basis of expert testimony always go to the weight of the evidence and
never go to admissibility. The decision below emphatically holds that the district court’s decision was an
“abuse of discretion because questions regarding the
31
factual underpinnings of the [expert witness’] opinion
affect the weight and credibility of the witness’ assessment, not its admissibility.” App., infra, at 20a-21a
(citation omitted). The district-court decision in question carefully and thoroughly explains why, under the
correct legal rule, the expert’s testimony does not have
a sufficient factual basis to be admitted. And the majority and dissenting opinions in the court of appeals
thoroughly ventilated the question presented.
2. A ruling in petitioners’ favor also would end this
case—making it an unusually compelling vehicle to
consider the question presented.
As Chief Judge Diaz explained, “[w]ithout [the expert’s] opinion, [respondent] can’t carry her burden to
present evidence sufficient to demonstrate” that she
was injured in any way by petitioners’ alleged actions.
App., infra, at 40a. That conclusion does not turn on
disagreements below about whether medical-monitoring costs constitute a sufficient injury for Article III
standing. Rather, without the challenged expert opinion, respondent simply “can’t establish [an] injury in
fact,” whether based on alleged monitoring costs or
any other alleged harm. Ibid. That is because the expert’s “model is the only evidence that * * * indicates
that [respondent] was exposed to EtO emitted by [petitioners’] operations.” Ibid.; see id. at 103a-105a.
The Fourth Circuit’s mistaken understanding of
Rule 702 was the only basis it gave for displacing the
district court’s careful decision about the flaws in the
facts and data underlying the expert’s opinion. The
Fourth Circuit gave no other reason to conclude that
the district court exceeded its wide latitude under the
abuse-of-discretion standard to assess whether it is
32
likely that the expert’s opinion has a sufficient basis—
and no such reason exists. 8
CONCLUSION
The petition for a writ of certiorari should be
granted.
Respectfully submitted,
JOHN L. EWALD
SUSANNA MOLDOVEANU
KIRKLAND & ELLIS LLP
601 Lexington Avenue
New York, NY 10022
(212) 446-4800
DAVID A. FUSCO
WESLEY A. PRICHARD
T. NATHAN TOWNSEND
K&L GATES LLP
210 Sixth Avenue
Pittsburgh, PA 15222
(412) 355-6500
DONALD B. VERRILLI, JR.
Counsel of Record
ELAINE J. GOLDENBERG
RACHEL G. MILLER-ZIEGLER
KYLE A. SCHNEIDER
MUNGER, TOLLES & OLSON LLP
601 Massachusetts Ave. NW
Suite 500E
Washington, DC 20001-5369
(202) 220-1100
Donald.Verrilli@mto.com
Counsel for Petitioners
February 2, 2026
Regardless, once the Fourth Circuit’s legal error about the scope
of Rule 702 is corrected, the court of appeals’ decision that the
expert’s testimony is admissible cannot survive, because that
court neither concluded itself “that it is more likely than not that
* * * the testimony is based on sufficient facts or data,” Fed. R.
Evid. 702(b), nor remanded to the district court to conduct that
analysis anew in light of some identified flaw. See n.7, supra.
8
APPENDICES
i
APPENDICES
Appendix A: Opinion of the United States
Court of Appeals for the Fourth Circuit
(August 18, 2025) ...................................................... 1a
Appendix B: Opinion of the United States
District Court for the Southern District of
West Virginia (March 20, 2024) ............................. 42a
Appendix C: Opinion of the United States
District Court for the Southern District of
West Virginia (May 13, 2024)................................. 89a
Appendix D: Order of the United States
Court of Appeals for the Fourth Circuit
Denying Rehearing (November 4, 2025) .............. 116a
Appendix E: Provisions Involved ........................ 117a
1a
APPENDIX A
No. 24-1491
UNITED STATES COURT OF APPEALS
FOR THE FOURTH CIRCUIT
Lee Ann SOMMERVILLE, individually, and on
behalf of all others similarly situated,
Plaintiff – Appellant,
v.
UNION CARBIDE CORPORATION; Covestro LLC,
Defendants – Appellees.
American Tort Reform Association; Chamber of
Commerce of the United States of America,
Amici Supporting Appellee.
Argued: January 29, 2025
Decided: August 18, 2025
Opinion
Reversed and remanded by published opinion. Judge
Benjamin wrote the opinion in which Judge Wynn
joined. Chief Judge Diaz wrote a dissenting opinion.
DEANDREA GIST BENJAMIN, Circuit Judge:
Plaintiff Lee Ann Sommerville appeals the district
court’s exclusion of her proposed expert, Dr. Ranajit
Sahu, and its grant of summary judgment to Defendants Union Carbide Corporation and Covestro LLC
for lack of standing. We now reverse.
I.
Sommerville, on behalf of herself and others similarly situated, sued Defendants Union Carbide Corporation and Covestro LLC (collectively “the Plant
Owners”) for alleged exposure to ethylene oxide
(“EtO”), a gas that causes cancer. Sommerville’s law-
2a
suit concerns a plant in South Charleston, West Virginia (“the Plant”), which Union Carbide, and then
Covestro, operated between 1978 and 2019. Sommerville alleges that the Plant emitted EtO into the atmosphere, that she breathed this EtO, and that this
exposure increased her risk of developing specific diseases. Sommerville alleges that she has a present
need to manage this increased risk of illness through
medical monitoring and diagnostic testing, and that
the Plant Owners should foot the bill. Sommerville
brought a single claim for medical monitoring under
West Virginia common law.
Sommerville challenges two orders the district
court issued. The first is an order excluding the opinions of her proffered expert, Dr. Sahu. The second is
an order granting the Plant Owners summary judgment. Sommerville timely appealed and we have jurisdiction. 28 U.S.C. § 1291.
II.
The district court acknowledged that West Virginia law recognizes medical monitoring claims. Nevertheless, it held that because Sommerville lacked a
“manifest” physical injury, she did not have Article
III standing. If the district court is correct, then
whether Dr. Sahu’s testimony was erroneously excluded is beside the point. So we begin with standing.
Our review is de novo. White Tail Park, Inc. v. Stroube, 413 F.3d 451, 459 (4th Cir. 2005).
A.
In Bower v. Westinghouse Electric Corp., 206
W.Va. 133, 522 S.E.2d 424 (1999), the Supreme Court
of Appeals of West Virginia recognized common law
claims for medical monitoring. Id. at 431. Plaintiffs
bringing medical monitoring claims seek “to recover
the anticipated costs of long-term diagnostic testing
3a
necessary to detect latent diseases that may develop
as a result of tortious exposure to toxic substances.”
Id. at 429. The tort is a “well-grounded extension of
traditional common-law tort principles.” See id.; see
also id. (collecting cases). 1
Medical monitoring claims originate from the traditional common law principle that individuals have
“legally protected interest[s] in avoiding physical injury.” See Bourgeois v. A.P. Green Indus., Inc., 716 So.
2d 355, 359 (La. 1998); Bower, 522 S.E.2d at 429–30.
Medical monitoring claims apply this principle to injuries where there is no visible “impact.” Bourgeois,
716 So. 2d at 358 (noting that “modern environmental toxins[ ] affect[ ] the body in ways that often do
not become manifest for many years”) (citing Hansen
v. Mountain Fuel Supply, 858 P.2d 970, 977 (Utah
1993)). “[T]he exposure itself and the concomitant
need for medical testing constitute the injury.” Bower,
522 S.E.2d at 430 (cleaned up and emphasis added)
(citing Hansen, 858 P.2d at 977).
Medical monitoring claims concern exposure to
“hazardous substance[s]” like “asbestos” or, in this
case, EtO and, by their nature, occur “without impact.” See Bourgeois, 716 So. 2d at 358 (“Unlike a car
crash, asbestos exposure is an accident almost always
without impact.”). The fact that exposure to a contaminant happens invisibly—so to speak—does not
sever the tort from its common law roots. The exposure “is still an accident that can have consequences
every bit as real as those sustained in a head-on colliBecause Bower v. Westinghouse Electric Corp., 206 W.Va. 133,
522 S.E.2d 424 (1999), does not articulate explicitly the common
law principles from which West Virginia’s medical monitoring
claim grew, we rely on Bourgeois v. A.P. Green Industries., Inc.,
716 So. 2d 355 (La. 1998), one of the cases which Bower cited.
1
4a
sion. In fact, it is precisely because asbestos”—or
EtO—“can have such deadly consequences that plaintiffs, regardless of whether or not they are currently
suffering from a disease, are often encouraged to
submit to regular diagnostic testing.” See id. at 358–
59.
Put simply, “an individual has an interest in
avoiding expensive diagnostic examinations just as
he or she has an interest in avoiding physical injury.”
Friends for All Child., Inc. v. Lockheed Aircraft Corp.,
746 F.2d 816, 826 (D.C. Cir. 1984). “When a defendant negligently invades this interest, the injury to
which is neither speculative nor resistant to proof, it
is elementary that the defendant should make the
plaintiff whole by paying for the examinations.” Id.;
Bower, 522 S.E.2d at 430 (quoting Friends for All
Child., 746 F.2d at 826, for this proposition). Or in
Bower’s own words, “[a]lthough the physical manifestations of an injury may not appear for years, the reality is that many of those exposed have suffered [a]
legal detriment; the exposure itself and the concomitant need for medical testing constitute the injury.”
522 S.E.2d at 430 (quoting Hansen, 858 P.2d at 977).
Given the injury’s nature—tortious exposure to a
known hazardous substance whose effects won’t appear for years but for which expensive medical testing is required today—Bower “reject[ed] the contention that a claim for future medical expenses must
rest upon the existence of present physical harm.” Id.
Bower quoted at length from Friends for All Children
to support this conclusion. See 522 S.E.2d at 430–31.
We do too:
Jones is knocked down by a motorbike which
Smith is riding through a red light. Jones
lands on his head with some force. Understandably shaken, Jones enters a hospital
5a
where doctors recommend that he undergo a
battery of tests to determine whether he has
suffered any internal head injuries. The tests
prove negative, but Jones sues Smith solely for
what turns out to be the substantial cost of the
diagnostic examinations.
...
[In such circumstances] it is clear that even in
the absence of physical injury Jones ought to
be able to recover the cost for the various diagnostic examinations proximately caused by
Smith’s negligent action. A cause of action allowing recovery for the expense of diagnostic
examinations recommended by competent
physicians will, in theory, deter misconduct,
whether it be negligent motorbike riding or
negligent aircraft manufacture. The cause of
action also accords with commonly shared intuitions of normative justice which underlie
the common law of tort. The motorbike rider,
through his negligence, caused the plaintiff, in
the opinion of medical experts, to need specific
medical services—a cost that is neither inconsequential nor of a kind the community generally accepts as part of the wear and tear of daily life. Under these principles of tort law, the
motorbiker should pay.
Friends for All Child., 746 F.2d at 825. Bower explicitly adopted this logic. 522 S.E.2d at 430–31.
Last, Bower articulated the elements required to
state a medical monitoring claim. To succeed on a
medical monitoring claim, a plaintiff must prove
(1) he or she has, relative to the general population, been significantly exposed; (2) to a
proven hazardous substance; (3) through the
6a
tortious conduct of the defendant; (4) as a
proximate result of the exposure, plaintiff has
suffered an increased risk of contracting a serious latent disease; (5) the increased risk of
disease makes it reasonably necessary for the
plaintiff to undergo periodic diagnostic medical examinations different from what would be
prescribed in the absence of the exposure; and
(6) monitoring procedures exist that make the
early detection of a disease possible.
Id. at 432–33.
B.
We turn to the district court’s standing decision.
The district court correctly recognized that Sommerville sought monetary relief to pay for the future cost
of medical monitoring. And because Sommerville
sought damages—not injunctive relief—the district
court also correctly concluded that Sommerville must
show a “present injury.” See Sommerville v. Union
Carbide Corp., No. 2:19-CV-00878, 2024 WL 2139394,
at *6 (S.D.W. Va. May 13, 2024) (hereinafter Sommerville II); TransUnion LLC v. Ramirez, 594 U.S.
413, 441, 141 S.Ct. 2190, 210 L.Ed.2d 568 (2021)
(“[T]he risk of future harm on its own does not support Article III standing for the plaintiffs’ damages
claim.”).
At this point, however, and as we explain later,
the district court’s analysis went off course. It framed
Sommerville’s injury as an increased risk of “eventually getting cancer.” Sommerville II, 2024 WL
2139394, at *7 (“Here, [Sommerville] seeks monetary
damages based on the premise that because [the
Plant Owners] emit EtO into the air and she, in turn,
breathes that air, [the Plant Owners] have put her
and proposed class members at higher risk of eventu-
7a
ally getting cancer.”); id. at *8 (“[H]er claim is based
entirely on the unsubstantiated possibility of a future
cancer diagnosis.”). Then, relying on TransUnion
LLC v. Ramirez, 594 U.S. 413, 141 S.Ct. 2190, 210
L.Ed.2d 568 (2021), the district court concluded that
because the “possibility of [a] future cancer diagnosis”
was not “concrete,” and because Sommerville did not
have a present physical injury, Sommerville lacked
Article III standing. See id. at *7–8 (“The Supreme
Court’s holding in TransUnion makes clear to me
that claims for medical monitoring seeking damages
without a manifest injury do not satisfy the injury-infact requirement for Article III standing.”) (footnote
omitted). The district court likewise held that Sommerville’s claim was not “ripe” because “not one of
[her] experts can say with any level of certainty that
[Sommerville] ... will develop cancer from [the Plant
Owners’] actions.” Id. at *11.
C.
Article III of the Constitution limits the jurisdiction of federal courts to actual “cases” or “controversies.” U.S. Const. art. III, § 2. Thus, it is a jurisdictional requirement that litigants be parties to a live
case or controversy. This standing requirement “is an
essential and unchanging part of the case-orcontroversy requirement of Article III.” Lujan v. Defenders of Wildlife, 504 U.S. 555, 560, 112 S.Ct. 2130,
119 L.Ed.2d 351 (1992) (citing Allen v. Wright, 468
U.S. 737, 751, 104 S.Ct. 3315, 82 L.Ed.2d 556 (1984)).
To establish standing, a party must establish, as
“the irreducible constitutional minimum,” three elements: (1) that it has suffered an “injury in fact” that
is both “concrete and particularized” and “actual or
imminent, not conjectural or hypothetical”; (2) that
there is “a causal connection between the injury and
the conduct complained of,” i.e., the injury is “fairly
8a
traceable” to the challenged action; and (3) that it is
“likely, as opposed to merely speculative, that the injury will be redressed by a favorable decision.” Id. at
560–61, 112 S.Ct. 2130 (internal quotation marks and
citations omitted); Burke v. City of Charleston, 139
F.3d 401, 405 (4th Cir. 1998). As to ripeness, “[t]he
doctrine ... prevents judicial consideration of issues
until a controversy is presented in clean-cut and concrete form.” Scoggins v. Lee’s Crossing Homeowners
Ass’n, 718 F.3d 262, 270 (4th Cir. 2013) (noting a case
is ripe “when the action in controversy is final and
not dependent on future uncertainties”) (quoting Miller v. Brown, 462 F.3d 312, 319 (4th Cir. 2006)).
TransUnion addressed “the Article III requirement that the plaintiff’s injury in fact be concrete” in
the context of a class action. 594 U.S. at 424, 141
S.Ct. 2190 (cleaned up). The named plaintiff in that
case brought a class action, alleging that TransUnion,
a credit reporting agency, had violated the Fair Credit Reporting Act by failing to use reasonable procedures before placing a misleading alert in his credit
file that labeled him as a potential terrorist, drug
trafficker, or serious criminal. Id. at 419–21, 141
S.Ct. 2190. He also asserted two claims based on
TransUnion’s having sent him two mailings that did
not comply with certain formatting requirements imposed by the statute. Id. at 421–22, 141 S.Ct. 2190.
The district court certified a class of more than
8,000 people who had the same misleading alert added to their credit files and who had also received similar mailings during a certain time period. A jury then
awarded each class member statutory and punitive
damages, and the Ninth Circuit largely affirmed the
judgment. Id. at 422, 141 S.Ct. 2190.
The Supreme Court reversed and remanded, holding that only a subset of the class had established Ar-
9a
ticle III standing to sue TransUnion for its failure to
use reasonable procedures to ensure the accuracy of
their credit files—namely, the 1,853 class members
whose credit reports had been provided to third-party
businesses and who had suffered “concrete reputational harm” as a result. Id. at 417, 141 S.Ct. 2190.
With respect to the two claims relating to the formatting defects in the mailings, the Court held that no
class member other than the named plaintiff had
demonstrated any concrete harm caused by the formatting errors, such that only he had standing to recover on those claims. Id. at 418, 141 S.Ct. 2190.
In explaining its decision, the Court emphasized
that, “under Article III, an injury in law is not an injury in fact” and that “[o]nly those plaintiffs who have
been concretely harmed by a defendant’s statutory violation may sue that private defendant over that violation in federal court.” Id. at 427, 141 S.Ct. 2190.
Put simply, “[n]o concrete harm, no standing.” Id. at
417, 141 S.Ct. 2190. The Court explained that while
“[t]he most obvious” concrete injuries are “tangible
harms, such as physical harms and monetary harms,”
“[v]arious intangible harms can also be concrete,” depending on whether they have “a close relationship to
harms traditionally recognized as providing a basis
for lawsuits in American courts.” Id. at 425, 141 S.Ct.
2190.
Then, the Court applied those principles to class
actions, observing that “standing is not dispensed in
gross.” Id. at 431, 141 S.Ct. 2190. It emphasized that
federal courts lack “the power to order relief to any
uninjured plaintiff, class action or not.” Id. (quoting
Tyson Foods, Inc. v. Bouaphakeo, 577 U.S. 442, 466,
136 S.Ct. 1036, 194 L.Ed.2d 124 (2016) (Roberts, C.J.,
concurring)). As a result, “[e]very class member must
have Article III standing in order to recover individu-
10a
al damages.” Id. Moreover, “plaintiffs must demonstrate standing for each claim that they press and for
each form of relief that they seek.” Id.
Finally, the Court also made clear that the form of
relief sought matters when assessing the sufficiency
of the alleged harm. Thus, while “a person exposed to
a risk of future harm may pursue forward-looking,
injunctive relief to prevent the harm from occurring,”
id. at 435, 141 S.Ct. 2190, “the risk of future harm on
its own does not support Article III standing for [a]
damages claim,” id. at 441, 141 S.Ct. 2190.
Applying these principles to the facts before it, the
Court held that the approximately 6,300 class members who failed to prove that the misleading alerts in
their credit reports were ever provided to a third party “did not suffer a concrete harm,” as necessary for
them to recover damages for the reasonable procedures claim. Id. at 439, 141 S.Ct. 2190. The Court rejected the argument that those class members had
“suffered a concrete injury for Article III purposes because the existence of misleading ... alerts in their internal credit files exposed them to a material risk
that the information would be disseminated in the
future to third parties and thereby cause them
harm.” Id. at 435, 141 S.Ct. 2190 (emphasis added)
(noting plaintiffs, despite seeking damages, tried to
demonstrate standing under the standard applicable
to injunctive relief).
And it was also unpersuaded by the plaintiffs’ argument that it could infer that those class members’
credit reports “were likely also sent to third parties ...
because all of the class members [had] requested copies of their reports, and consumers usually do not request copies unless they are contemplating a transaction that would trigger a credit check.” Id. at 438–39,
141 S.Ct. 2190. Rejecting that contention, the Court
11a
reasoned that “[t]he plaintiffs had the burden to
prove at trial that their reports were actually sent to
third-party businesses” and that “[t]he inferences on
which the argument rests are too weak to demonstrate that the reports of any particular [class member were] sent to third-party businesses.” Id. at 439,
141 S.Ct. 2190.
Finally, the Court concluded that, other than the
named plaintiff, none of the class members had
“demonstrated that the format of TransUnion’s mailings”—even if not in compliance with the statute—
caused them “any harm at all,” let alone “a harm
with a close relationship to a harm traditionally recognized as providing a basis for a lawsuit in American courts.” Id. at 440, 141 S.Ct. 2190.
In sum, TransUnion stands for the proposition
that “a plaintiff does not ‘automatically satisf[y] the
injury-in-fact requirement’ whenever a statute [or
state common law] ... ‘grants a person a [ ] right and
purports to authorize that person to sue to vindicate
that right.’ ” See Fernandez v. RentGrow, Inc., 116
F.4th 288, 294 (4th Cir. 2024) (quoting TransUnion,
594 U.S. at 426, 141 S.Ct. 2190). Article III requires a
“concrete injury.” Id. (quoting Spokeo, Inc. v. Robins,
578 U.S. 330, 341, 136 S.Ct. 1540, 194 L.Ed.2d 635
(2016)). “Accordingly, ‘[o]nly those plaintiffs who have
been concretely harmed by a defendant’s statutory violation [or tortious act] may sue that private defendant over that violation in federal court.’ ” See id.
(quoting TransUnion, 594 U.S. at 427, 141 S.Ct.
2190).
D.
i.
We reverse the district court’s order granting the
Plant Owners summary judgment. Sommerville has
12a
Article III standing.
To begin, the district court misstated the harm for
which medical monitoring plaintiffs like Sommerville
seek recovery. Sommerville’s alleged injury is not an
“increased risk of cancer development due to the alleged EtO emissions.” Sommerville II, 2024 WL
2139394, at *7. Sommerville’s injury is her “exposure
itself” to “environmental toxins” tortiously emitted by
the Plant Owners, “[which] affect the body in ways
that often do not become manifest for several years”
and “the concomitant need [to pay] for medical testing” today to mitigate an increased risk of illness
which Sommerville would not bear but for the Plant
Owners’ actions. See Bower, 522 S.E.2d at 430 (emphasis added); Bourgeois, 716 So. 2d at 358 (cleaned
up); Friends for All Child., 746 F.2d at 825 (“The
[tortfeasor], through his negligence, caused the plaintiff, in the opinion of medical experts, to need specific
medical services—a cost that is neither inconsequential nor of a kind the community generally accepts as
part of the wear and tear of daily life. Under these
principles of tort law, the [tortfeasor] should pay.”).
Framed properly, Sommerville’s injury is concrete
and ripe.
Sommerville alleges that the Plant Owners wrongfully exposed her to EtO in such great quantities that
her chance of contracting a serious latent disease increased to the point that she must, in a qualified physician’s opinion, pay for and undergo periodic diagnostic medical examinations now. See Bower, 522
S.E.2d at 433. West Virginia law permits Sommerville to seek recovery for this harm, which is grounded in the “traditional common-law principle[ ]” of
“avoiding physical injury.” Bourgeois, 716 So. 2d at
359; Bower, 522 S.E.2d at 429–30; see TransUnion,
594 U.S. at 424–25, 141 S.Ct. 2190. Sommerville
13a
might not have a visible injury like a broken arm, but
this does not make her injury any less actual, concrete, or serious. See Bourgeois, 716 So. 2d at 358 (observing that “asbestos exposure is an accident almost
always without impact. Nevertheless, it is still an accident that can have consequences every bit as real as
those sustained in a head-on collision”).
Lest there be any doubt that the injury requisite
to bring a medical monitoring claim is not merely
“conjectural,” Sommerville II, 2024 WL 2139394, at
*8, the Supreme Court of Appeals of West Virginia
has emphasized that the six Bower factors “establish[
] an extremely high bar for a plaintiff to overcome before there can be any recovery for medical monitoring.” In re Tobacco Litig., 215 W.Va. 476, 600 S.E.2d
188, 194 (2004). These factors require Sommerville to
demonstrate such significant exposure to a hazardous
substance as to render monitoring a present medical
necessity. This injury is actual and concrete. So,
Sommerville has Article III standing.
The Plant Owners’ principal argument for affirming the district court’s grant of summary judgment is
unconvincing. The Plant Owners contend that the
district court didn’t hold that medical monitoring
plaintiffs without a manifest physical injury always
lack Article III standing. Appellees’ Br. (ECF No. 24)
at 53 (“[Sommerville] argues against a strawman she
puts forth—that the District Court decided that no
medical-monitoring plaintiff could ever have Article
III standing at any stage of litigation.”). Instead, the
Plant Owners insist that the district court granted
them summary judgment because Sommerville
“lacked admissible evidence [of] her exposure.” Id. at
56 (arguing that the district court’s exclusion, by prior order, of Dr. Sahu’s testimony left Sommerville
without evidence of exposure to EtO). This argument
14a
is counterfactual. 2
The district court explicitly ruled that Sommerville lacked an actual injury because “[t]he Supreme
Court’s holding in TransUnion ma[d]e[ ] clear to [it]
that claims for medical monitoring seeking damages
without a manifest injury do not satisfy the ... requirement[s] for Article III standing.” See Sommerville II, 2024 WL 2139394, at *7. As explained above
and as we reiterate here, this conclusion—along with
the factual assertions on which it rested—was wrong.
Sommerville’s claim is not that the Plant Owners’
EtO emissions may have harmed her by putting her
“at a higher risk of eventually getting cancer.” Sommerville II, 2024 WL 2139394, at *7; see TransUnion,
594 U.S. at 435, 141 S.Ct. 2190 (rejecting argument
that roughly 6,300 class members had “suffered a
concrete injury for Article III purposes because the
existence of misleading ... alerts in their internal
credit files exposes them to a material risk that the
information w[ill] be disseminated in the future to
third parties and thereby cause them harm”). Rather,
Sommerville’s injury is that the Plant Owners exposed her to EtO in such quantities that she must, in
Having previously excluded Dr. Sahu’s testimony, the district
court could have granted the Plant Owners summary judgment
against Sommerville not for “lack of standing,” but for want of
necessary evidence. See Sommerville v. Union Carbide Corp.,
No. 2:19-CV-00878, 2024 WL 2139394, at *12 n.7 (S.D.W. Va.
May 13, 2024) (noting that “if [the district court] had to proceed
to the merits of the action,” it would have granted the Plant
Owners summary judgment due to Sommerville’s failure to meet
Bower’s first element). The district court, however, granted
summary judgment based on standing. Further, even if the district court had granted the Plant Owners summary judgment for
failure to meet Bower’s first element, that conclusion would
have been erroneous—as explained in Section III, Dr. Sahu’s
testimony was wrongfully excluded.
2
15a
a qualified physician’s opinion, pay for and undergo
periodic diagnostic medical examinations now. This
injury is no less concrete than the injury suffered by
the 1,853 class members in TransUnion whose credit
reports had actually been provided to third-party
businesses and who had suffered “concrete reputational harm.” See TransUnion, 594 U.S. at 417, 141
S.Ct. 2190.
ii.
The dissent frames Sommerville’s injury like the
district court—as an increased risk of “develop[ing]
cancer.” See Diss. Op. at 428 (“Sommerville claims
that she’s at an increased risk of developing cancer
and that the risk creates a present need for medical
monitoring. ...Though the future harm here—
cancer—is serious, it’s certainly not impending. The
record doesn’t show who in the putative class (if anyone) will develop cancer or when (if ever).”). Then, relying on Beck v. McDonald, 848 F.3d 262 (4th Cir.
2017), it concludes Sommerville’s injury is too speculative to establish Article III standing. Diss. Op. at
427 – 28.
In Beck, the plaintiffs sued Department of Veterans Affairs officials after their medical records were
stolen from a Veterans Affairs medical center. The
plaintiffs sought damages for two injuries: (1) the “increased risk of future identity theft” and (2) “credit
monitoring services.” Id. at 273, 276. The court held
that both injuries were “too speculative” to confer Article III standing. See id. at 274; id. at 276 (holding
second injury was “a repackaged version” of the first
and that plaintiffs could not establish standing by
seeking “costs they incurred in response to a speculative threat”) (cleaned up).
In holding that the plaintiffs’ claims were too
16a
speculative, Beck emphasized the “attenuated chain
of possibilities” that the plaintiffs relied on to establish their injury. Id. at 275 (quoting Clapper v. Amnesty Intern. USA, 568 U.S. 398, 410, 133 S.Ct. 1138,
185 L.Ed.2d 264 (2013)). This chain included “assum[ing] that the thief targeted the stolen items for
the personal information they contained. And ...
[that] the thieves select[ed], from thousands of others, the personal information of the named plaintiffs
and attempt[ed] successfully to use that information
to steal their identifies.” Id. (emphasis added).
Here, Beck is inapposite. Sommerville’s alleged injury does not rest on an “attenuated chain of possibilities.” Nor does it rest on an unknown third party’s
actions. It exists already. Her injury is a present
physical one—“exposure itself” to “environmental toxins” the Plant Owners tortiously emitted and “the
concomitant need [to submit to and pay] for medical
testing” today to mitigate an increased risk of illness.
See Bower, 522 S.E.2d at 430 (emphasis added). Put
differently, Sommerville is not suing about a “speculative threat” that depends on a third party’s future
acts. Beck, 848 F.3d at 277 (cleaned up). She is suing
about her current need for “specific medical services—a cost that is neither inconsequential nor of a
kind the community generally accepts as part of the
wear and tear of daily life.” Friends for All Child.,
746 F.2d at 825. At bottom then, like the district
court, the dissent misapprehends both the nature and
immediateness of the harm for which Sommerville
seeks redress.
***
For the reasons stated above, we hold that plaintiffs properly alleging the elements of West Virginia’s
medical monitoring tort have Article III standing.
Sommerville has done so, and we reverse the district
17a
court’s order granting the Plant Owners summary
judgment for lack of standing.
III.
We now address the district court’s exclusion of
Sommerville’s proposed expert Dr. Sahu.
A.
Under Fed. R. Evid. 702, trial judges act as gatekeepers to “ensure that any and all scientific testimony ... is not only relevant, but reliable.” Daubert v.
Merrell Dow Pharms., Inc., 509 U.S. 579, 588, 113
S.Ct. 2786, 125 L.Ed.2d 469 (1993). While “Rule 702
was intended to liberalize the introduction of relevant
expert evidence ... court[s] must recognize that due to
the difficulty of evaluating their testimony, expert
witnesses have the potential to ‘be both powerful and
quite misleading.’ ” Westberry v. Gislaved Gummi AB,
178 F.3d 257, 261 (4th Cir. 1999) (quoting Daubert,
509 U.S. at 595, 113 S.Ct. 2786) (internal citation
omitted). Therefore, a trial judge, faced with a proffer
of expert scientific testimony, must conduct “a preliminary assessment of whether the reasoning or
methodology underlying the testimony is scientifically valid and of whether that reasoning or methodology properly can be applied to the facts in issue.”
Daubert, 509 U.S. at 592–93, 113 S.Ct. 2786. The
proponent of the testimony must establish its admissibility by a preponderance of proof. See id. at 592 n.
10, 113 S.Ct. 2786 (citing Bourjaily v. United States,
483 U.S. 171, 175–76, 107 S.Ct. 2775, 97 L.Ed.2d 144
(1987)); Fed. R. Evid. 702.
In Daubert v. Merrell Dow Pharmaceuticals, Inc.,
509 U.S. 579, 113 S.Ct. 2786, 125 L.Ed.2d 469 (1993),
the Supreme Court identified several factors that
may bear on a judge’s determination of the reliability
of an expert’s testimony. See 509 U.S. at 592–94, 113
18a
S.Ct. 2786. Those factors include: (1) whether a theory or technique can be or has been tested; (2) whether
it has been subjected to peer review and publication;
(3) whether a technique has a high known or potential rate of error and whether there are standards
controlling its operation; and (4) whether the theory
or technique enjoys general acceptance within a relevant scientific community. See id at 592–94, 113 S.Ct.
2786.
In Kumho Tire Co. v. Carmichael, 526 U.S. 137,
119 S.Ct. 1167, 143 L.Ed.2d 238 (1999), the Supreme
Court noted that the factors discussed in Daubert
were neither definitive, nor exhaustive. Id. at 150–
51, 119 S.Ct. 1167. The Court explained that particular factors may or may not be pertinent in assessing
reliability, “depending on the nature of the issue, the
expert’s particular expertise, and the subject of his
testimony.” See id. The Court further emphasized
that the objective of Daubert’s gatekeeping requirement is to “make certain that an expert ... employs in
the courtroom the same level of intellectual rigor that
characterizes the practice of an expert in the relevant
field.” See id. at 152, 119 S.Ct. 1167.
Courts of appeals apply an abuse of discretion
standard when reviewing a trial court’s decision to
admit or exclude expert testimony. See Gen. Elec. Co.
v. Joiner, 522 U.S. 136, 138–39, 118 S.Ct. 512, 139
L.Ed.2d 508 (1997). The Supreme Court also has emphasized that “the trial judge must have considerable
leeway in deciding in a particular case how to go
about determining whether particular expert testimony is reliable.” See Kumho Tire, 526 U.S. at 152,
119 S.Ct. 1167.
B.
To establish liability, Sommerville acknowledges
19a
that she must put forth admissible expert testimony
to establish Bower’s first element—that she was, relevant to the general population, “significantly exposed” to a proven hazardous substance. 522 S.E.2d
at 432– 33. Accordingly, Sommerville offered Dr. Sahu to testify about the fate and transport of the
Plant’s EtO emissions between 1984 and 2019. Dr.
Sahu sought to provide “technical expertise, analysis,
methodology, and opinions regarding various environmental and pollutant fate and transport issues
relating to emissions of [EtO] from [the Plant] ... to
ultimately determine the potential exposure levels of
[Sommerville] and the proposed class members.”
Sommerville v. Union Carbide Corp., No. 2:19-CV00878, 2024 WL 1204094, at *2 (S.D.W. Va. Mar. 20,
2024) (hereinafter Sommerville I).
Dr. Sahu modeled EtO emissions using the
“AERMOD” dispersion model, a computer program.
J.A. 524. Before running AERMOD, however, Dr. Sahu had to select the inputs AERMOD would use to
generate his EtO modeling. These inputs included
source data 3, receptor data 4, and meteorological data.
J.A. 524.
Source data means EtO “emissions sources” including “specification and locations of source units, historical emissions rates,
and source parameters.” J.A. 524. “Source parameters” are details describing the locations from which EtO was omitted. Id.
525. “Point source” or “stack emissions” are “air releases that
occur through identifiable confined air streams, such as stacks,
ducts or pipes.” Sommerville v. Union Carbide Corp., No. 2:19CV-00878, 2024 WL 1204094, at *10 n.5 (S.D.W. Va. Mar. 20,
2024) (cleaned up). And “fugitive emissions” are “releases to air
that don’t occur through a confined air stream” such as via
“equipment leaks.” Id.
3
“The AERMOD model allows the user to input a set of receptors, which are locations at which the model will predict hourly
concentrations due to the input source emissions.” J.A. 526.
4
20a
The district court excluded Dr. Sahu’s proposed
testimony. For a plethora of supposedly independently-sufficient reasons, the district court found Dr. Sahu’s testimony was unreliable. The district court did
not question AERMOD itself but took issue with Dr.
Sahu’s choice of source and meteorological data.
First, the district court found that Dr. Sahu’s
choice of source parameters rendered his report unreliable. Sommerville I, 2024 WL 1204094, at *10. To
set his source parameters, Dr. Sahu relied on data
the West Virginia Department of Environmental Protection created. Further, for the years 1985–1989, Dr.
Sahu modeled all emissions as fugitive. The district
court faulted Dr. Sahu for these choices, holding that
both decisions were based on “assumptions ... with
little to no scientific basis.” Id. at *11.
Excluding Dr. Sahu for these choices was an
abuse of discretion. Dr. Sahu presented detailed reasons for his challenged assumptions. See, e.g., id. (acknowledging Dr. Sahu’s assertion that the Plant
Owners’ lack of record keeping limited Dr. Sahu’s
choice of “site-specific data to base his model on”);
J.A. 514 (explaining why Dr. Sahu chose to model all
Plant emissions as fugitive for 1985–1989); id. 568
(further explaining Dr. Sahu’s modeling choices and
assumptions as to fugitive emissions). The district
court, however, simply ignored or discounted Dr. Sahu’s proffered explanations in favor of those that the
Plant Owners’ expert, Dr. Ranjit Machado, offered.
See Sommerville I, 2024 WL 1204094, at *10–11.
At bottom, the district court’s analysis was not a
true critique of Dr. Sahu’s “methodology,” but a veiled
credibility determination based on Dr. Sahu’s choice
of which data to input into his model. This was an
abuse of discretion because “questions regarding the
factual underpinnings of the [expert witness’] opinion
21a
affect the weight and credibility of the witness’ assessment, not its admissibility.” See Bresler v. Wilmington Tr. Co., 855 F.3d 178, 195 (4th Cir. 2017)
(cleaned up); Rappuhn v. Primal Vantage Co., No. 2310050, 2024 WL 2930448, at *4 (11th Cir. June 11,
2024) (“[C]rediting one expert over another ... misapplies Daubert and intrudes on the province of the jury.”).
Second, the district court found Dr. Sahu’s testimony was unreliable because he did not “validate”
Union Carbide’s self-reported emissions data before
inputting them into AERMOD. Sommerville I, 2024
WL 1204094, at *12–13 (Union Carbide self-reported
1984 data); id. at *13–14 (Union Carbide selfreported data 1990–2019). The district court did not
cite controlling case law imposing a “validation” requirement. Nor did it explain, in practical terms, how
Dr. Sahu was supposed to undertake “validation.”
Excluding Dr. Sahu for failing to “validate” his data was a glaring abuse of discretion. Nothing in Rule
702 requires an expert witness to “validate” data.
Fed. R. Evid. 702. The district court’s requirement
that Dr. Sahu do just that, however, was extratextual, an error of law, and thus an abuse of discretion
per se. See New York City Transit Auth. v. Express
Scripts, Inc., 588 F. Supp. 3d 424, 445 (S.D.N.Y.
2022) (rejecting argument that expert failed to validate data and noting “the [c]ourt has not found[ ]
precedent requiring experts to validate the data underlying each source on which they rely in order to
satisfy the reliability threshold for admissibility”); see
also Daubert, 509 U.S. at 596, 113 S.Ct. 2786 (“Vigorous cross-examination, presentation of contrary evidence, and careful instruction on the burden of proof
are the traditional and appropriate means of attacking shaky but admissible evidence.”).
22a
Said differently, the district court again disagreed
with Dr. Sahu’s choice of data and excluded Dr. Sahu’s testimony as a result, even though our caselaw
forbids as much. See Baxter v. Comm’r of I.R.S., 910
F.3d 150, 158 (4th Cir. 2018) (affirming admission of
expert and rejecting challenge to his selection of certain data finding that “to the extent that Taxpayers[ ]
disagree with Kolbe’s estimates of the costs of obtaining a ‘good’ or ‘normal’ loan, ‘such challenges ... affect
the weight and credibility of [Kolbe’s] assessment, not
its admissibility’ ”) (citing Bresler, 855 F.3d at 196).
The district court made further related errors concerning its critique of Dr. Sahu’s emissions data selections. For the year 1984, Dr. Sahu relied on data
Union Carbide reported to the West Virginia Air Pollution Control Commission. When Union Carbide reported this data to authorities, it included a letter
claiming its figures should not be taken at face value
because they were “drastically overstated.” Sommerville I, 2024 WL 1204094, at *12. In the district
court’s opinion, because Union Carbide had cast
doubt on its own data, Dr. Sahu’s use of the data rendered his opinion unreliable.
This conclusion was an abuse of discretion for two
reasons. First, Dr. Sahu provided reasons for why he
did not believe Union Carbide’s claim that its 1984
data were inaccurate. Second, and more fundamentally, excluding Dr. Sahu on this basis again 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.” See Bresler, 855 F.3d at
195 (cleaned up).
The district court committed a similar error when
it held that Dr. Sahu’s report was unreliable because
of the data Dr. Sahu based emissions on for the years
23a
1985–1989. For this period, Dr. Sahu based EtO
emissions on the “Toxic Air Pollutant Facility Registration Summary Sheets” the Plant Owners provided
to regulatory authorities. The district court took issue
with this choice because it believed that the “values
listed [on the summary sheets were] estimates for
maximum toxic air pollutant emissions, not actual
emissions.” Sommerville I, 2024 WL 1204094, at *13
(cleaned up). The district court, however, ignored Dr.
Sahu’s testimony justifying his contrary interpretation of the summary sheets.
While Dr. Machado argued that the summary
sheets were only potential emissions, Dr. Sahu testified that the “substantial variation” over time in the
reported figures led him to infer Union Carbide was
reporting actual emissions. J.A. 261–62. Such a “factual dispute is best settled by a battle of the experts
before the fact finder, not by judicial fiat.” See City of
Pomona v. SQM N. Am. Corp., 750 F.3d 1036, 1048–
49 (9th Cir. 2014); see also Johnson v. Mead Johnson
& Co., LLC, 754 F.3d 557, 562 (8th Cir. 2014) (“The
district court in the instant case violated these liberal
admission standards by resolving doubts in favor of
keeping the testimony out and relying upon its own
assessment of the correctness of the expert opinions.”); Westberry, 178 F.3d at 261 (“[T]he court need
not determine that the expert testimony a litigant
seeks to offer into evidence is irrefutable or certainly
correct. As with all other admissible evidence, expert
testimony is subject to being tested by ‘[v]igorous
cross-examination, presentation of contrary evidence,
and careful instruction on the burden of proof.’ ”)
(quoting Daubert, 509 U.S. at 596, 113 S.Ct. 2786)
(alteration adopted); see also McCullock v. H.B. Fuller
Co., 61 F.3d 1038, 1044 (2d Cir. 1995) (noting that
perceived faults in doctor’s differential diagnosis were
24a
matters for cross-examination that did not affect admissibility).
Third, the district court took issue with Dr. Sahu’s
choice of meteorological inputs for AERMOD. To
model dispersion patterns around the Plant, Dr. Sahu
had to input wind speed and direction data. Dr. Sahu
inputted data from various sites and elevations to
create his model. The district court concluded Dr. Sahu’s testimony was unreliable because “[w]ind directions are highly variable ... [and] a single location—
such as [Sommerville’s] residence—cannot have multiple wind speeds coming from various directions at
one specific time.” Sommerville I, 2024 WL 1204094,
at *16. The district court further found Dr. Sahu’s
testimony unreliable because Dr. Sahu used 1985–
1986 onsite meteorological data from the Plant for
the years 1984–2019.
These conclusions were abuses of discretion. Beyond possibly misstating the science of wind 5—and
unnecessarily attempting to make scientific findings
to justify its exclusion of Dr. Sahu 6—the district court
Multiple wind speeds from different directions at the same
time at a single geographic location is not only possible but
widely accepted. See, e.g., What Causes Tornadoes?, NOAA (describing how tornadoes are created and noting that “[c]onditions
are ripe for tornadoes when the air becomes very unstable, with
winds at different altitudes blowing in different directions or at
different speeds—a condition called wind shear”) (emphasis added), https://perma.cc/9MYS-P7CK.
5
We agree with the dissent that the district court should not
have fashioned itself as an “amateur scientist[ ],” and excluded
Dr. Sahu’s testimony on the basis that “a single location ... cannot have multiple wind speeds coming from various directions at
one specific time.” Sommerville I, 2024 WL 1204094, at *16;
Diss. Op. at 432 n.9; cf. Daubert, 509 U.S. at 601, 113 S.Ct. 2786
(Rehnquist, C.J., concurring in part and dissenting in part)
(“[Rule 702] imposes on [courts] [n]either the obligation [n]or the
6
25a
again conflated admissibility with the weight a factfinder might attribute Dr. Sahu’s testimony based on
his choice of data. Simultaneously, the district court
ignored Dr. Sahu’s testimony as to why using wind
data from various altitudes was proper given South
Charleston’s mountainous geography and why Dr.
Sahu chose to use onsite data from 1985–1986 to
model 1984–2019. See J.A. 532–33 (explaining that
because of the “elevated point source[s]” of certain
“flare emissions,” Dr. Sahu used data from Yeager
Airport, roughly 285 meters elevation); id. 572 (explaining that the only onsite data available at the
Plant was from 1985–1986, that the Plant Owners
had supplied no other data and, in Dr. Sahu’s professional experience, any variation would not be significant); see also Daubert, 509 U.S. at 596, 113 S.Ct.
2786 (“Vigorous cross-examination, presentation of
contrary evidence, and careful instruction on the
burden of proof are the traditional and appropriate
means of attacking shaky but admissible evidence.”).
Fourth, the district court faulted Dr. Sahu for how
he chose to calculate “background” EtO levels. “Background” refers to exposure levels experienced by the
general population as opposed to the levels Sommerville alleges she was exposed to due to the Plant
Owners’ negligence. The district court found Dr. Sahu’s testimony was unreliable because Dr. Sahu used
data produced by the United States Environmental
Protection Agency (EPA) instead of data from the
West Virginia Department of Environmental Protection—data the district court described as being more
“local.” Sommerville I, 2024 WL 1204094, at *19. The
authority to become amateur scientists”). We include the information in the preceding footnote only to emphasize the danger
trial courts run when, as the district court did here, they attempt to exclude expert testimony in this fashion.
26a
district court found Dr. Sahu was “cherry-picking”
data. Id. at *18–19. This finding was an abuse of discretion.
Dr. Sahu didn’t “cherry-pick data.” Cherry-picking
data means engaging in a “[r]esult-driven analysis”
that “undermines principles of the scientific method.”
See In re Lipitor (Atorvastatin Calcium) Mktg., Sales
Pracs. & Prods. Liab. Litig. (No II) MDL 2502, 892
F.3d 624, 634 (4th Cir. 2018). In Lipitor, this court
affirmed the trial court’s exclusion of the plaintiffs’
expert where he “cho[se] to include in his report the
results of some tests he performed (which supported
the plaintiffs’ argument) but exclude the results of
another (which did not).” Id. at 634–35.
Dr. Sahu did nothing of the sort. Instead, Dr. Sahu chose to use the EPA’s data because he found it
more representative of Sommerville’s claims. True,
the EPA had reservations about aspects of its data
set. See J.A. 814 (stating that while the EPA was
“confident” in EtO data collected “downwind of facilities,” the EPA had also detected EtO levels close to
the detection limit, implying “greater uncertainty in
its measurement and ... less confiden[ce] in [its] accuracy”). But the West Virginia data the district court
held Dr. Sahu should have used came with disclaimers too. Id. 1786 (“The project involved four (4) 24hour sampling events. Four days of data cannot be
used to calculate risk over a 70-year period.”). Put
simply, the weight to give Dr. Sahu’s choice of EtO
background data had nothing to do with the admissibility of his testimony. Though framed as a “reliability” question, the district court again waded into
credibility determinations. Excluding Dr. Sahu on
this basis was an abuse of discretion.
Last, the district court abused its discretion when
it concluded that Dr. Sahu’s report was unreliable be-
27a
cause Dr. Sahu had wrongly maintained Covestro’s
emissions rates constant from 1984–2019 in AERMOD. To so find, the district court ignored Dr. Sahu’s
testimony that while he had erroneously held
Covestro’s emissions constant in his initial report, he
had corrected this error in his supplemental report.
Id. 1188–93 (“I ... reran the model using the varying
emission rates for the Covestro sources. In this supplemental report I show the results of this revised
modeling and also comparisons to the prior constant
emission rate results.”) (cleaned up). Therefore, the
district court’s exclusion of Dr. Sahu on this basis
was likewise an abuse of discretion.
In sum, none of the reasons for which the district
court excluded Dr. Sahu’s testimony were proper.
And in accordance with Federal Rules of Evidence
104(a) and 702, Sommerville has established by a
preponderance of evidence that Dr. Sahu’s testimony
is admissible. Therefore, Dr. Sahu’s exclusion was an
abuse of discretion. 7
The dissent is unclear “what line” we “intend to draw.” Diss.
Op. at 431. We do not question that a district court can decide
“that an expert’s opinion lacks sufficient support in the record”
or that “there is simply too great an analytical gap between [an
expert’s] data and the opinion proffered.” Id.; Gen. Elec. Co. v.
Joiner, 522 U.S. 136, 146, 118 S.Ct. 512, 139 L.Ed.2d 508 (1997).
Rather, we underscore that a district court may not exclude expert testimony based on (1) its mere disagreement with an expert’s choice of data or (2) its own assessment of the correctness
of an expert’s opinions. See Bresler v. Wilmington Tr. Co., 855
F.3d 178, 195 (4th Cir. 2017) (noting “questions regarding the
factual underpinnings of the [expert witness’] opinion affect the
weight and credibility of the witness’ assessment, not its admissibility”) (cleaned up); Rappuhn v. Primal Vantage Co., No. 2310050, 2024 WL 2930448, at *4 (11th Cir. June 11, 2024)
(“[C]rediting one expert over another ... misapplies Daubert and
intrudes on the province of the jury.”). These errors permeate
7
28a
IV.
For the reasons stated above, we reverse the district court’s grant of summary judgment to the Plant
Owners and its exclusion of Dr. Sahu.
REVERSED AND REMANDED
the district court’s order excluding Dr. Sahu and dictate reversal.
29a
DIAZ, Chief Judge, dissenting:
West Virginia courts have opened their doors to
claims for damages, like Sommerville’s, in which the
only claimed injury is a present need for medical
monitoring. In my view, Article III standing principles prevent us from doing the same. Because my colleagues conclude otherwise, I respectfully dissent.
I.
West Virginia allows plaintiffs to bring medical
monitoring claims “to recover the anticipated costs of
long-term diagnostic testing necessary to detect latent diseases that may develop as a result of tortious
exposure to toxic substances.” Bower v. Westinghouse
Elec. Corp., 206 W.Va. 133, 522 S.E.2d 424, 429
(1999). Plaintiffs must show—as relevant here—that
an exposure to a hazardous substance put them at a
“significantly increased risk of contracting a particular disease” that makes diagnostic testing “reasonably necessary.” Id. at 433. They don’t need to show
that they’ve experienced any physical harm, nor any
certainty (or even likelihood) that a disease will occur. Id.
But to get into federal court, a state law injury
isn’t enough. As my colleagues agree, Sommerville
(who alleges she was exposed to a carcinogen emitted
from Defendants’ operations at a manufacturing facility in South Charleston, West Virginia near her
home) must show that she’s suffered an injury in fact
sufficient for Article III.
Sommerville doesn’t claim that she’s been physically harmed. Nor does she claim that her injury in
fact is an increased risk of developing cancer. And for
good reason, because a “risk of future harm ... cannot,
by itself, establish concrete injury to have standing to
seek damages.” Penegar v. Liberty Mut. Ins. Co., 115
30a
F.4th 294, 302 (4th Cir. 2024) (citing TransUnion
LLC v. Ramirez, 594 U.S. 413, 436, 141 S.Ct. 2190,
210 L.Ed.2d 568 (2021)).
Instead, Sommerville’s asserted injury is the “necessary medical monitoring costs resulting from toxic
exposure.” Appellant’s Br at 12. For the majority,
that’s enough for standing. 1 I disagree and would instead hold that medical monitoring costs (incurred or
anticipated), without more, can’t confer standing to
seek damages in federal court.
Our decision in Beck v. McDonald, 848 F.3d 262
(4th Cir. 2017), explains why. There, plaintiffs sued
after their medical records were stolen from a Veterans Affairs medical center. Id. at 267–68. They
brought data privacy claims seeking damages and declaratory and injunctive relief. Id. They claimed two
injuries in fact: (1) “the increased risk of future identity theft,” id. at 273, and (2) “the cost of measures to
guard against identity theft, including the costs of
credit monitoring services,” that they had incurred or
would incur, id. at 276.
But we rejected the first because, under the circumstances of the data breaches, the risk that the
plaintiffs’ identities would be stolen was too speculaNeither the Bower court, in its assessment of the common-law
principles underlying medical monitoring claims, nor the majority, in its injury-in-fact analysis, disaggregate the exposure from
the costs of medical monitoring. Though both mention the exposure, both focus on the economic harm of medical monitoring
costs stemming from the exposure. So the asserted injury in fact
here appears to be the costs of medical monitoring, not the exposure that creates the need for those costs.
1
I don’t read the majority opinion to hold that exposure alone is
an injury in fact. Nor could I join such a novel holding without
substantially more analysis than what the majority offers.
31a
tive. 2 Id. at 274. And the second was “merely a repackaged version” of the first. Id. at 276 (cleaned up).
It too failed because “costs ... incurred in response to
a speculative threat” can’t confer standing. 3 Beck, 848
F.3d at 276–77 (quoting Clapper v. Amnesty Int’l
USA, 568 U.S. 398, 416, 133 S.Ct. 1138, 185 L.Ed.2d
264 (2013)); see also Remijas v. Neiman Marcus Grp.,
LLC, 794 F.3d 688, 694 (7th Cir. 2015) (“Mitigation
expenses do not qualify as actual injuries where the
harm is not imminent.”).
So too here. Sommerville claims that she’s at an
increased risk of developing cancer and that the risk
creates a present need for medical monitoring—the
costs of which are her injury in fact. But to confer Article III standing, these costs must be based on a future harm that is “certainly impending.” Clapper, 568
U.S. at 409, 416, 133 S.Ct. 1138.
Recall that Sommerville doesn’t press that her injury in fact is
an increased risk of developing cancer.
2
The plaintiffs in Clapper v. Amnesty International USA, 568
U.S. 398, 133 S.Ct. 1138, 185 L.Ed.2d 264 (2013), sought injunctive relief, and Sommerville seeks damages. Still, Clapper’s reasoning with respect to the mitigation injury asserted there applies here. Id. at 415, 133 S.Ct. 1138 (costs incurred to protect
confidentiality of communications based on risk of surveillance).
3
In each case, plaintiffs claimed to be suffering “present injury”
because the risk of a harm in the future created the need to incur certain costs now and in the future (and, in Clapper, it had
forced them to incur such costs already). Id. at 401, 133 S.Ct.
1138. That type of injury can be addressed by eliminating the
risk that the future harm will occur (via injunction) or by shifting the costs to the defendant (via damages). A plaintiff who
lacks standing to seek an injunction because the underlying “future harm ... is not impending” shouldn’t have standing to seek
damages for costs incurred based on that same speculative
harm. Id.
32a
Though the future harm here—cancer—is serious,
it’s not certainly impending. The record doesn’t show
who in the putative class (if anyone) will develop cancer or when (if ever). Because the risk of this harm
coming to pass, even if heightened, is uncertain, monitoring costs based on such a risk aren’t enough for
Article III standing.
According to the majority, I “misapprehend[ ]” the
injury it recognizes. Majority Opinion at 421. I think
not.
I don’t rely on Beck because I see here a similarly
“attenuated chain of possibilities.” Id. (quoting Beck,
848 F.3d at 275). Nor is that alone what Beck relied
on to decide the case. And I would know—I wrote it!
Beck instructs that for costs stemming from a potential future harm to be an injury in fact, the underlying future harm must be a non-speculative one. The
future harm underlying the credit-monitoring-cost
injury asserted in Beck was not that the plaintiffs’
medical records had been stolen—it was the risk of
identity theft. Similarly, the future harm underlying
the medical-monitoring-cost injury asserted here is
not the EtO exposure—it’s the risk of developing cancer. In each case, plaintiffs seek to “monitor” something that may occur, not the event that’s already occurred.
Here and in Beck, the future harm underlying the
monitoring-cost injury is speculative. It doesn’t matter that the future harm in Beck isn’t speculative in
precisely the same manner as here. Because the underlying future harm is speculative, costs needed or
incurred based on that harm can’t be an injury in
fact.
33a
II.
There’s yet another reason Sommerville lacks
standing. The district court, in my view, correctly excluded Dr. Ranajit Sahu’s expert testimony. And
without Sahu’s testimony, Sommerville can’t meet
her burden at summary judgment to demonstrate an
injury in fact.
A.
Sommerville hired Dr. Sahu to reconstruct ethylene oxide, or “EtO,” 4 emissions from the Defendants’ South Charleston industrial facility between
1984 and 2019 and to create an air dispersion model 5
to estimate cumulative EtO exposure levels at points
near the facility.
According to Sahu, this model could estimate an
individual’s cumulative EtO exposure based on where
they lived and the years they lived there. Sommerville’s other experts would use these cumulative exposure estimates and background EtO levels—which
Dr. Sahu also estimated—to calculate each class
EtO is a human carcinogen. Our Current Understanding of
Ethylene Oxide (EtO), EPA, https://www.epa.gov/hazardous-airpollutants-ethylene-oxide/our-current-understanding-ethyleneoxide-eto [https://perma.cc/F53C-JPUV]. Long-term exposure to
EtO increases the risk of certain cancers, while “[s]hort-term
inhalation exposure to high amounts of EtO can cause headache,
dizziness, nausea, fatigue, respiratory irritation[,] ... and, in
some cases, ... gastrointestinal distress.” Id.
4
Air dispersion modeling uses mathematical formulas to simulate “the atmospheric processes that disperse [an air] pollutant
emitted by a source.” Air Quality Dispersion Modeling, EPA
(Nov.
21,
2024),
https://www.epa.gov/scram/air-qualitydispersion-modeling [https://perma.cc/F7C6-L6C6]. An air dispersion model “can be used to predict concentrations” of an air
pollutant at locations around the source. Id.
5
34a
member’s relative risk of developing certain cancers.
When faced with expert testimony, the district
court’s gatekeeping responsibility is to “ensur[e] that
[the] testimony both rests on a reliable foundation
and is relevant to the task at hand.” Daubert v. Merrell Dow Pharms., Inc., 509 U.S. 579, 597, 113 S.Ct.
2786, 125 L.Ed.2d 469 (1993) (emphases added). To
be reliable, an expert’s opinion must be “based on scientific, technical, or other specialized knowledge and
not on belief or speculation,” and any “inferences
must be derived using scientific or other valid methods.” Nease v. Ford Motor Co., 848 F.3d 219, 229 (4th
Cir. 2017) (emphasis omitted) (quoting Oglesby v.
Gen. Motors Corp., 190 F.3d 244, 250 (4th Cir. 1999)).
The question isn’t whether we would have admitted Dr. Sahu’s testimony in the first instance, but
whether the district court abused its discretion in excluding it. The Supreme Court has cautioned us
against being “overly stringent” in answering this
question. Gen. Elec. Co. v. Joiner, 522 U.S. 136, 143,
118 S.Ct. 512, 139 L.Ed.2d 508 (1997). After all, “[i]t
is very much a matter of discretion with the court
whether to receive or exclude the evidence,” so we
should not reverse “unless the ruling is manifestly
erroneous.” McKiver v. Murphy-Brown, LLC, 980
F.3d 937, 962 (4th Cir. 2020) (quoting Gen. Elec. Co.,
522 U.S. at 142, 118 S.Ct. 512).
Here, the district court concluded that Sahu’s expert testimony wasn’t well-grounded in the facts and
data available and was thus unreliable. Sommerville
v. Union Carbide Corp., No. 19-CV-00878, 2024 WL
1204094, at *1 (S.D. W. Va. Mar. 20, 2024). The district court didn’t abuse its discretion. In fact, the
court was right.
1.
35a
The majority faults the district court for focusing
on Dr. Sahu’s justifications for his inputs into the
“AERMOD” modeling system, rather than on the system itself. According to the majority, this flouts
Daubert, which directs courts to focus on methodology. Not so.
The AERMOD modeling system and Sahu’s model
aren’t the same. The fact that the AERMOD modeling system could (in theory) produce a sufficiently reliable dispersion model 6 doesn’t settle whether Sahu’s
dispersion model was sufficiently reliable. Instead,
the reliability of Sahu’s model depends on the reliability of the inputs, as Dr. Sahu himself agreed. 7 E.g.,
J.A. 219 (agreeing that “the accuracy of the model
bears a strong positive relationship to the correct inputs being used ... that represent the actual condition
in the facilities in its emissions sources”).
True, Daubert directs us to focus on “principles
and methodology, not on the conclusions that they
generate.” 509 U.S. at 595, 113 S.Ct. 2786. But 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. In re Lipitor
(Atorvastatin Calcium) Mktg., Sales Pracs. & Prods.
Liab. Litig. (No II) MDL 2502, 892 F.3d 624, 641 (4th
Cir. 2018); see also id. at 643–44.
A modeling expert’s methodology doesn’t end with
selecting a modeling system. The expert must also
develop the inputs and assumptions used to create
The Defendants don’t challenge the reliability of the AERMOD
modeling system. So I assume that the system doesn’t introduce
any separate Daubert concerns here.
6
7
Put more bluntly, garbage in, garbage out.
36a
the model. 8 Here, the district court had to consider
whether those inputs and assumptions are supported
by “scientifically valid” “reasoning or methodology,”
Daubert, 509 U.S. at 592–93, 113 S.Ct. 2786, such
that the resulting model is “based on sufficient facts
or data,” Fed. R. Evid. 702(b). And that’s precisely
what the district court did.
But, says the majority, “questions regarding the
factual underpinnings of the expert witness’[s] opinion affect the weight and credibility of the witness’[s]
assessment, not its admissibility.” Majority Opinion
at 423, 424 (cleaned up) (quoting Bresler v. Wilmington Tr. Co., 855 F.3d 178, 195 (4th Cir. 2017)).
I can’t tell what line my colleagues intend to draw
here, especially because Daubert inquiries are inherently “tied to the facts of a particular case.” Kumho
Tire Co. v. Carmichael, 526 U.S. 137, 150, 119 S.Ct.
1167, 143 L.Ed.2d 238 (1999) (cleaned up). Yet they
can’t possibly mean that district courts may not decide that an expert’s opinion lacks sufficient support
in the record, cf. Fed. R. Evid. 702(b), or conclude
“that there is simply too great an analytical gap between [an expert’s] data and the opinion proffered,”
Gen. Elec. Co., 522 U.S. at 146, 118 S.Ct. 512.
We’ve faulted district courts for “abdicat[ing]
[their] responsibility” with respect to expert testimony based on the belief “that the question of whether
an expert’s opinion had an adequate basis in fact
should be handled by opposing counsel through cross
examination and in jury argument.” Tyger Constr. Co.
Even Dr. Sahu considered developing these inputs to be his
methodology. The “Methodology” section of his expert report focuses exclusively on how he “reconstruct[ed] operations and
identif[ied] emission and waste sources.” J.A. 467–68; see also
J.A. 494.
8
37a
v. Pensacola Constr. Co., 29 F.3d 137, 143 (4th Cir.
1994); see also Sardis v. Overhead Door Corp., 10
F.4th 268, 281–82 (4th Cir. 2021).
The district court recognized its duty here and
honored it. We should commend the court, not reverse its ruling.
2.
Nor can I agree with the majority that the district
court’s concern about a lack of validation was misplaced. See Sommerville, 2024 WL 1204094, at *12,
*14. Validation (as in “data validation”) can refer to
specific protocols used to confirm data quality. But I
take the district court to have used “validate” in a
more colloquial sense—as in “substantiate” or “support.”
The district court had good reason to be concerned
about Dr. Sahu’s failure to justify the assumptions he
made in creating the inputs for the dispersion model.
See Daubert, 509 U.S. at 590, 113 S.Ct. 2786 (“Proposed testimony must be supported by appropriate
validation—i.e., ‘good grounds,’ based on what is
known.” (emphases added)). Here again, the district
court was simply doing its job as the “gatekeeper[ ] of
expert testimony.” Sardis, 10 F.4th at 275 (cleaned
up).
3.
What’s left are a series of concerns squarely within the district court’s purview—that the inputs were
“speculative” and “premised on assumptions that
[did] not accurately represent the Defendants’ operations in South Charleston.” Sommerville, 2024 WL
1204094, at *1; see, e.g., In re Lipitor, 892 F.3d at
633–35 (unrepresentative data set, flawed logic, unsound assumptions); EEOC v. Freeman, 778 F.3d 463,
38a
466–67 (4th Cir. 2015) (unexplained discrepancies in
data set, analytical fallacies); Belville v. Ford Motor
Co., 919 F.3d 224, 229 (4th Cir. 2019) (unsupported
assumptions). I can’t agree with the majority’s attempt to recast these problems as a “mere disagreement with [Sahu’s] choice of data” or an “assessment
of the correctness” of his ultimate opinions. Majority
Opinion at 427 n.7 (emphases omitted).
Sahu’s model purports to estimate actual emissions. Yet he relied on values that expressly didn’t
represent actual emissions. Sommerville, 2024 WL
1204094, at *13. Sahu himself “identified inconsistencies in [the] reported EtO emissions,” J.A. 1188,
but he “[n]onetheless ... used [those] emissions for ...
various years in updating [his] modeling,” J.A. 1190.
And Sahu ignored telltale signs that there might
be a problem with the emissions values he used. For
example, his model shows that in 1984 the cumulative EtO exposure at a point a half mile from the
South Charleston facility was 100 times greater than
in other years, J.A. 535, yet that outlier raised no red
flags for Sahu—at least none that warranted an explanation.
The model also required meteorological inputs. To
develop them, Sahu combined meteorological data
from three locations—one year of hourly wind speed
and wind direction data from near the South Charleston facility (which he supplemented with data from
an airport five miles away); twice-daily upper air data from a town fifty miles away; and other meteorological parameters also from the airport. But Sahu
never explained why the data from some distance
away was representative of the conditions near the
39a
facility. 9 See Tyger Constr. Co., 29 F.3d at 143.
Sahu filled in gaps in the emissions and meteorological data with assumptions. That isn’t problematic
on its own. “Trained experts commonly extrapolate
from existing data.” Gen. Elec. Co., 522 U.S. at 146,
118 S.Ct. 512. But those assumptions must be “connected to existing data” by more than just “the ipse
dixit of the expert.” Id.
Sahu justified some of his assumptions in his initial report, but he simply identified others. And his
rebuttal report and deposition testimony provided little support beyond his say-so.
In many instances, Sahu held a value (e.g., emissions, operations) from one year constant over several
years (or, for the meteorological data, for the entire
thirty-year period at issue). But as the district court
correctly recognized, he failed to explain why such
values were unlikely to change significantly from
year to year.
The district court “identified and articulated clear
... concerns it had about the manner in which [Dr.
Sahu] reached his conclusions.” In re Lipitor, 892
F.3d at 638. I’m not left with “a definite and firm conIt strikes me as unwise for courts to opine on “the science of
wind”—whatever that entails—unless absolutely necessary. Majority Opinion at 425 & n.5; cf. Daubert, 509 U.S. at 601, 113
S.Ct. 2786 (Rehnquist, C.J., concurring in part and dissenting in
part) (“[Rule 702] imposes on [courts] [n]either the obligation
[n]or the authority to become amateur scientists.”). That’s especially true here, where we’re unaided by briefing or record evidence. Whatever direction the science of wind blows, Dr. Sahu
failed to support his meteorological assumptions. And whatever
the district court’s “scientific finding[s],” Majority Opinion at
425, it acted well within its discretion to conclude as much,
Sommerville, 2024 WL 1204094, at *17.
9
40a
viction that the [district] court ... committed a clear
error of judgment” in carrying out its gatekeeping responsibility. Freeman, 778 F.3d at 466. To the contrary, the district court’s decision to exclude Dr. Sahu’s
opinion is right on the merits.
In holding otherwise, the majority wrongly invites
district courts to “delegate [their] gatekeeping responsibility to the jury.” Nease, 848 F.3d at 231.
B.
Without Dr. Sahu’s opinion, Sommerville can’t
carry her burden to present evidence sufficient to
demonstrate Article III standing.
At summary judgment, Sommerville “cannot rest
on mere allegations but must set forth evidence
which ... would establish the elements of Article III
standing.” Fernandez v. RentGrow, Inc., 116 F.4th
288, 295 (4th Cir. 2024). Though we view the evidence in Sommerville’s favor, id., we “may not consider inadmissible evidence” at summary judgment,
Giles v. Nat’l R.R. Passenger Corp., 59 F.4th 696, 704
(4th Cir. 2023).
So even if the need for and costs of medical monitoring is an injury in fact, Sommerville can’t establish
that injury in fact without Dr. Sahu’s opinion. His
model is the only evidence that, for example, indicates that Sommerville was exposed to EtO emitted
by the Defendants’ operations. And without Sahu’s
estimates of her cumulative exposure, Sommerville’s
other experts couldn’t calculate her relative risk of
developing certain cancers, or opine on the significance of that risk, or her need for medical monitoring.
III.
I have no quarrel with the West Virginia Supreme
Court of Appeals’ reasons for recognizing a medical
41a
monitoring cause of action, which the majority aptly
recounts. But the need for and costs of medical monitoring—without more—isn’t an injury in fact sufficient for Article III standing. Even if it were, Sommerville can’t demonstrate such an injury without
Dr. Sahu’s expert testimony, which the district court
properly excluded.
Because the majority holds otherwise, I dissent.
42a
APPENDIX B
UNITED STATES DISTRICT COURT
FOR THE SOUTHERN DISTRICT OF
WEST VIRGINIA
CHARLESTON DIVISION.
Lee Ann SOMMERVILLE, et al., Plaintiffs,
v.
UNION CARBIDE CORPORATION, Defendant.
CIVIL ACTION NO. 2:19-cv-00878
Signed March 20, 2024
MEMORANDUM OPINION AND ORDER
JOSEPH R. GOODWIN,
DISTRICT JUDGE
UNITED
STATES
Pending before the court are two motions to limit
the opinions and testimony of Dr. Ranajit (Ron) Sahu
filed by Defendants Union Carbide Corporation
(“UCC”), [ECF No. 309], and Covestro LLC
(“Covestro”), [ECF No. 327], respectively. Plaintiff
Lee Ann Sommerville (“Plaintiff”) filed a response to
UCC’s motion, [ECF No. 343], and a response to
Covestro’s motion, [ECF No. 342], on July 10, 2023.
For the reasons discussed below, I GRANT both motions, [ECF Nos. 309, 327], and ORDER that the testimony and reports of Dr. Ranajit Sahu be excluded
as unreliable.
Upon detailed review of the expert reports, I find
that the opinions of Dr. Sahu are not based upon sufficient facts or data because the inputs he uses in the
air model are speculative and are premised on assumptions that do not accurately represent the Defendants’ operations in South Charleston. As such,
there are serious doubts about whether such opinions
43a
are the product of reliable principles and methods,
which have also not been reliably applied to the facts
of this case. For these reasons, which I discuss in
greater detail below, I GRANT both motions, [ECF
Nos. 309, 327], and ORDER that the testimony and
reports of Dr. Ranajit Sahu be excluded as unreliable.
I. Background
The named Plaintiff brought this proposed medical monitoring class action against Defendants UCC
and Covestro, as owners and operators of a manufacturing facility located in South Charleston, West Virginia, for their alleged “dangerous and reckless emission of ethylene oxide (“EtO”),” a known human carcinogen, between 1984 and 2019. [ECF No. 85, ¶¶ 1–
2].
A. Ethylene Oxide Exposure
EtO is a colorless, odorless gas produced in large
volumes at some chemical manufacturing facilities.
See Our Current Understanding of Ethylene Oxide
(EtO), U.S. Env’t Prot. Agency, https://www.epa.gov/
hazardous-air-pollutants-ethylene-oxide/our-currentunderstanding-ethylene-oxide-eto#what (last visited
Mar. 11, 2024). According to the Environmental Protection Agency (“EPA”), EtO is a known human carcinogen, and regular, long-term exposure to EtO can
cause certain cancers of the white blood cells, including non-Hodgkin lymphoma, myeloma, and lymphocytic leukemia. Id. Because the primary way EtO enters the environment is by release into the air, individuals who live near facilities that release EtO into
the outdoor air may be exposed to EtO. Id.
According to Plaintiff, UCC is “the world’s leading
producer of EtO,” and “the South Charleston Plant is
one of the only facilities in the [United States] that
manufactures EtO.” [ECF No. 85, ¶ 28]. UCC has
44a
“owned and operated the South Charleston Plant
since at least 1978,” and in 2015, Covestro began “operat[ing] polyols facilities” at the South Charleston
plant. Id. ¶¶ 41, 44. Plaintiff claims that UCC and
Covestro “operated without sufficient pollution controls to limit and/or eliminate the emissions of toxic
EtO and, as a result, exposed thousands of residents
in neighboring areas” to the carcinogen “for at least
41 years.” Id. ¶¶ 48, 53. As a result of the allegedly
“negligent and tortious” emissions of EtO, Plaintiff
claims that she and the proposed class members
“have suffered significant exposure to hazardous EtO
gases relative to the general population in the [United States],” id. ¶ 59, and are, therefore, “at an increased risk of developing cancer,” making “periodic
diagnostic medical examinations [ ] reasonably necessary,” id. ¶ 62. Plaintiff seeks an award of “the quantifiable costs” of medical monitoring for the benefit of
all proposed class members due to their alleged exposure. Id. ¶¶ 84–86.
B. Expert Opinion of Dr. Ranajit Sahu
Plaintiff relies upon a number of expert opinions
in seeking to establish the elements of her claim. One
such opinion is offered by Dr. Ranajit Sahu, a mechanical engineer, who was engaged to provide “technical expertise, analysis, methodology, and opinions
regarding various environmental and pollutant fate
and transport issues relating to emissions of [EtO]
from Union Carbide’s Institute and [the] South
Charleston facilities” (collectively, the “Facilities”) to
ultimately determine the potential exposure levels of
Plaintiff and the proposed class members. [ECF No.
309-3, at 6]. Dr. Sahu provided his Expert Report on
February 17, 2023. [ECF No. 309-3]. Defendants seek
to exclude the opinions in this report, as well as Dr.
Sahu’s related testimony.
45a
1. Dr. Sahu’s Background and Experience
Dr. Sahu is “a mechanical engineer with over thirty years of experience in the fields of environmental,
mechanical, and chemical engineering.” Id. After obtaining a Bachelor of Technology in mechanical engineering from the Indian Institute of Technology in
Kharagpur, India in 1983, Dr. Sahu attended the California Institute of Technology in Pasadena, California from 1984 to 1988, where he received a Master of
Science and Doctorate degree in mechanical engineering. Id. at 7. Dr. Sahu also has over twenty-seven
years of “project management experience” and has
“provided consulting services to numerous private
sector, public sector, and public interest group clients” over the past twenty-five years. Id. His experiences include “design and specification of pollution
control equipment for a wide range of emissions
sources,” “multimedia environmental regulatory
compliance,” “transportation air quality impact analysis,” “air quality ... permitting,” “multimedia/multipathway human health risk assessment for toxics,”
and “air dispersion modeling.” Id. at 6–7. Dr. Sahu
has also taught numerous university courses in air
pollution, process hazard analysis, air pollution controls, transportation and air quality, and engineering.
Id. at 7.
2. Dr. Sahu’s Summary of Opinions
In his February 17, 2023, report, Dr. Sahu outlines his findings related to the EtO emissions from
operations at the Facilities. His summary of opinions
is listed below:
(i) There were numerous sources of EtO air
emissions from Union Carbide’s West Virginia
Operations (WVO). EtO was used extensively
in various production processes. EtO was
46a
brought into the [Facilities] from elsewhere,
and subsequently distributed, stored, and processed. This handling and use of EtO created
significant opportunities for EtO releases into
the ambient air. Examples include: EtO emissions from various storage tanks, where EtO
was present in the materials being stored, and
therefore emitted from such tanks; EtO emissions from various fugitive components—such
as valves, pump seals, connectors, flanges, and
others—which were present throughout the
[Facilities], including in all handling, storage,
distribution, and processing areas; EtO emissions from so-called extended cookout operations at the reactors; and EtO emissions from
flaring of waste gases containing EtO.
(ii) In spite of the many sources of EtO at the
[Facilities], there was no direct testing of EtO
mass emissions to the ambient air from any of
the sources under representative conditions
over the many years of EtO-related operations.
While direct monitoring of the open-flame
stack flares at the [Facilities] would have been
problematic, no efforts were made to use other
types of thermal combustion devices (such as
enclosed stack flares, thermal oxidizers, etc.)
for waste gas disposal, which could have been
tested and monitored.
There was no direct testing of the many fugitive components that emitted EtO. The Leak
Detection and Repair (LDAR) program that
was used for some period of time relied on assumed emission factors and effectiveness of
the program with no verification.
47a
There was no testing of EtO emissions from
any of the tanks that stored EtO containing
materials.
There was little direct testing of EtO from extended cookout operations, which were
claimed to be appropriate regulatory controls
for various hazardous air pollutants, including
EtO.
(iii) Since there was no direct testing of EtO
emissions from the many sources of EtO, and
certainly therefore no testing under representative conditions, all emissions of EtO developed and/or reported by Defendants used
engineering estimates. However, for engineering estimates to be proper, they needed to be
grounded by site specific data.
Site specific data is not constant at chemical
manufacturing operations such as at the operations in question. Union Carbide’s estimates
of EtO emissions relied on sporadic and unsupported assumptions; and, crucially, in the
case of flares, on “surrogate” parameters that
bore no relation to actual operating conditions
or actual emissions.
As such it is my opinion that EtO emissions
were underestimated significantly from all
sources. In this report, I have highlighted the
example of underestimation of the EtO emissions from the flares, via the use of an unrealistically high flare control efficiency, which did
not and could not have represented every-day
operations of the flares.
(iv) The few verification tests that were conducted at the facilities in order to meet regulatory requirements showed that actual opera-
48a
tions deviated considerably from regulatory
requirements. In the case of the flares, preliminary tests conducted prior to the required
compliance tests, showed significant failures.
Due to the lack of prior testing at the facilities,
these significant failures indicate that inadequate conditions existed for persistent periods
of time prior to the failed tests. This is supported by internal discussions among Union
Carbide managers explicitly acknowledging
that the control efficiencies they reported to
regulators rarely matched reality.
(v) Failed tests were remedied for regulatory
compliance demonstrations in order to make
them “pass.” However, the failed tests were
never reported to regulators as required. Once
a “passing” test was obtained, there is no record that Union Carbide monitored subsequent
flare operating conditions, or had any policies
or procedures to ensure that necessary passing
conditions were maintained. Thus, the compliance tests were unrepresentative of usual or
normal operations and were meaningless.
Worse, it is my opinion, that by conducting
sham compliance tests, Defendants were in violation of applicable regulatory requirements,
such as the need to conduct testing under representative conditions and to keep proper records demonstrating continuous compliance.
(vi) Based on conservative (i.e., still likely underestimated emissions) recalculation of emissions and by modeling such emissions using
appropriate and standard air dispersion modeling, it is my opinion that persons in the surrounding community were exposed to significant concentrations of EtO.
49a
(vii) Collectively, it is my opinion that Defendants’ conduct relating to the emissions of EtO
was irresponsible and exhibited a knowing and
willful disregard of both their regulatory requirements and the health and safety of persons in the surrounding community.
Id. at 8–10.
C. Defendant UCC’s Motion to Exclude [ECF
No. 309]
UCC asserts that Dr. Sahu should be excluded as
a witness for four primary reasons. First, UCC argues that Dr. Sahu’s air modeling opinions do not
“fit” the facts of the case. [ECF No. 310, at 3–4]. 1 Second, UCC asserts that Dr. Sahu’s air modeling opinions suffer from “serious methodological flaws” which
render them unreliable because they do not rely on
an accurate historical reconstruction and were formulated using “patently unreliable emissions data” that
Dr. Sahu failed to validate. Id. at 11, 13, 15. Third,
UCC contends that Dr. Sahu’s source configurations
do not reliably represent historical conditions. Id. at
19. Finally, UCC claims that Dr. Sahu did not employ
a reliable method to estimate background levels of
EtO in the community and combined contradictory
meteorological data that leads to impossible results.
Id. at 20. For these reasons, UCC argues that “Dr.
Sahu’s work ... falls far short of the standard set by
this [c]ourt,” id. at 3, and should be excluded pursuant to Rule 702 of the Federal Rules of Evidence and
Daubert v. Merrell Dow Pharm., Inc., 509 U.S. 579
(1993).
Unless otherwise stated, the page numbers cited correspond to
CM/ECF page numbers.
1
50a
Plaintiff rebuts these arguments, arguing that
UCC “does not mount a true Daubert challenge.”
[ECF No. 343, at 3 (quoting TWFS, Inc. v. Shaefer,
325 F.3d 234, 240 (4th Cir. 2003))]. Rather, Plaintiff
claims that UCC “mounts an attack on the data inputs to Dr. Sahu’s air model by disputing the accuracy of the data and the assumptions that are required
to fill gaps in the data, while failing to offer any different conclusions that might be reached with different data.” Id. She argues that the court should deny
UCC’s motion because “questions regarding the factual underpinnings of an expert’s opinion affect the
weight and credibility of the opinion, not admissibility.” Id. (citing Bresler v. Wilmington Tr. Co., 855
F.3d 178, 195 (4th Cir. 2017)).
D. Defendant Covestro’s Motion to Exclude
[ECF No. 327]
Likewise, Defendant Covestro asserts that the
court should exclude the testimony and reports of Dr.
Sahu because they are irrelevant to Plaintiff’s claims
against Covestro and are also fatally unreliable. [ECF
No. 327, at 1]. Specifically, Covestro contends that (1)
the opinions are “irrelevant as to Covestro” because
Dr. Sahu is “unfamiliar” with Covestro’s operations in
South Charleston; (2) the air model is “irrelevant and
unreliable as to Covestro because its inputs do not
reflect the reality” of its operations in South Charleston; (3) the figures produced by Dr. Sahu’s air model
are “irrelevant and unreliable because they do not
represent exposure or dose;” and (4) the opinions “regarding the exposure of the general population” are
“irrelevant and unreliable because Dr. Sahu does not
know the background levels of [EtO] in the air.” Id.
In response, Plaintiff argues that Covestro, too,
fails to “mount a true Daubert challenge,” but instead, “challenges the factual underpinnings, data
51a
inputs, and relevancy of Dr. Sahu’s opinions.” [ECF
No. 342, at 3]. She claims that Dr. Sahu had properly
considered Covestro’s South Charleston operations
and that his opinions are based on those operations.
Id. She also argues that Dr. Sahu’s opinions on “significant EtO exposure are relevant,” that the “meteorological inputs are reliable,” and that the EPA’s
National Air Toxics Assessment (“NATA”) database—
which Dr. Sahu used as a data source—“provides the
most appropriate background level.” Id. Further,
while Plaintiff concedes that there was a “minor error
with a data input” related to Covestro’s operations,
she asserts that “Dr. Sahu properly updated his expert report” to correct the issue, 2 and that regardless,
the “minor error” was not sufficient grounds to exclude his opinions. Id. For these reasons, Plaintiff
asks the court to deny Covestro’s motion. Id. at 12.
II. Legal Standard
Under Federal Rule of Evidence 702, expert testimony is admissible if it (1) will “help the trier of fact
to understand the evidence or to determine a fact in
issue” (2) is “based upon sufficient facts or data,” and
(3) is “the product of reliable principles and methods,”
which (4) have been “reliably appli[ed] ... to the facts
of the case.” Fed. R. Evid. 702. A two-part test governs the admissibility of expert testimony: evidence is
admissible if “it rests on a reliable foundation and is
relevant.” Daubert, 509 U.S. at 597 (1993). The proponent of expert testimony does not have the burden
to “prove” anything. He must, however, “come forward with evidence from which the court can determine that the proffered testimony is properly admisThere is currently pending a motion filed by Covestro to strike
this supplemental expert report as untimely under Federal Rule
of Civil Procedure 26(e). See [ECF No. 300].
2
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sible.” Md. Cas. Co. v. Therm-O-Disc., Inc., 137 F.3d
780, 783 (4th Cir. 1998).
The district court has an important role as the
gatekeeper of expert opinions and testimony. Because
“expert witnesses have the potential to be both powerful and quite misleading,” the court must “ensure
that any and all scientific testimony ... is not only relevant, but reliable.” Cooper v. Smith & Nephew, Inc.,
259 F.3d 194, 199 (4th Cir. 2001) (internal markings
omitted) (citing Westberry v. Gislaved Gummi AB,
178 F.3d 257, 261 (4th Cir. 1999) and Daubert, 509
U.S. at 588, 595). I “need not determine that the proffered expert testimony is irrefutable or certainly correct”—“[a]s with all other admissible evidence, expert
testimony is subject to testing by ‘[v]igorous crossexamination, presentation of contrary evidence, and
careful instruction on the burden of proof.’ ” United
States v. Moreland, 437 F.3d 424, 431 (4th Cir. 2006)
(quoting Daubert, 509 U.S. at 596) (alteration in original); see also Md. Cas. Co., 137 F.3d at 783 (noting
that “[a]ll Daubert demands is that the trial judge
make a ‘preliminary assessment’ of whether the proffered testimony is both reliable ... and helpful”).
Daubert outlines specific factors to guide the overall relevance and reliability determinations that apply to all expert evidence. They include “(1) whether
the particular scientific theory can ‘be (and has been)
tested’; (2) whether the theory ‘has been subjected to
peer review and publication’; (3) the ‘known or potential rate of error’; (4) the ‘existence and maintenance
of standards controlling the technique’s operation’;
and (5) whether the technique has achieved ‘general
acceptance’ in the relevant scientific or expert community.” United States v. Crisp, 324 F.3d 261, 266
(4th Cir. 2003) (quoting Daubert, 509 U.S. at 593–94).
With respect to relevancy, Daubert explains:
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Expert testimony which does not relate to any
issue in the case is not relevant and, ergo, nonhelpful. The consideration has been aptly described by Judge Becker as one of “fit.” “Fit” is
not always obvious, and scientific validity for
one purpose is not necessarily scientific validity for other, unrelated purposes....Rule 702‘s
“helpfulness” standard requires a valid scientific connection to the pertinent inquiry as a
precondition to admissibility.
Id. at 591–92 (internal citations omitted).
Despite these factors, “[t]he inquiry to be undertaken by the district court is ‘a flexible one’ focusing
on the ‘principles and methodology’ employed by the
expert, not on the conclusions reached.” Westberry,
178 F.3d at 261 (quoting Daubert, 509 U.S. at 594–
95); see also Kumho Tire Co. v. Carmichael, 526 U.S.
137, 150 (1999) (“We agree with the Solicitor General
that ‘[t]he factors identified in Daubert may or may
not be pertinent in assessing reliability, depending on
the nature of the issue, the expert’s particular expertise, and the subject of his testimony.’ ”) (citation
omitted); see also Crisp, 324 F.3d at 266 (citing Kumho for the proposition “that testing of reliability
should be flexible and that Daubert’s five factors neither necessarily nor exclusively apply to every expert”). However, “conclusions and methodology are
not entirely distinct from one another.” Gen. Elec. Co.
v. Joiner, 522 U.S. 136, 146 (1997).
Additionally, some scholars have opined that
“[Daubert] has proven especially inappropriate and
inadequate in evaluating model reliability. The problems that plague all models—namely uncertainty and
a lack of transparency—are exacerbated in environmental-tort litigation.” Matthew W. Swinehart, Remedying Daubert’s Inadequacy in Evaluating the Ad-
54a
missibility of Scientific Models Used in Environmental-Tort Litigation, 86 Tex. L. Rev. 1281, 1283 (2008)
[hereinafter Remedying Daubert’s Inadequacy]; see
also Wendy Wagner et al., Misunderstanding Models
in Environmental and Public Health Regulation, 18
N.Y.U. Envt’l L.J. 293, 324 (2010) [hereinafter Misunderstanding Models] (“There are significant conflicts between the Supreme Court’s deterministic test
for admissibility of expert testimony (embodied in
Daubert v. Merrell Dow Pharmaceuticals) and the
true nature of models.”). Ultimately, a district court
has broad discretion in determining whether to admit
or exclude expert testimony, and “the trial judge
must have considerable leeway in deciding in a particular case how to go about determining whether
particular expert testimony is reliable.” Cooper, 259
F.3d at 200 (quoting Kumho Tire, 526 U.S. at 152);
see also United States v. Hankey, 203 F.3d 1160, 1167
(9th Cir. 2000) (“A trial court not only has broad latitude in determining whether an expert’s testimony is
reliable, but also in deciding how to determine the
testimony’s reliability.”) (internal quotation marks
and citations omitted).
III. Discussion
Before reaching the analysis of Dr. Sahu’s expert
opinions, I will first address Plaintiff’s contention
that the instant motions raise questions affecting the
weight and credibility of Dr. Sahu’s opinions rather
than their admissibility and the inference that the
issues are, thus, a matter for the jury, not the court.
See [ECF No. 343, at 3].
As part of its “gatekeeping function,” the court
must “ensure[ ] that expert evidence is sufficiently
relevant and reliable when it is submitted to the jury.” Nease v. Ford Motor Co., 848 F.3d 219, 231 (4th
Cir. 2017) (emphasis in original). “Thus, the trial
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court must probe the reliability and relevance of expert testimony any time ‘such testimony’s factual basis, data, principles, methods, or their application are
sufficiently called into question.’ ” EEOC v. Freeman,
778 F.3d 463, 472 (4th Cir. 2015) (Agee, J., concurring) (quoting Kumho, 526 U.S. at 149). “[T]he fact
that an expert witness [is] ‘subject to a thorough and
extensive examination’ does not ensure the reliability
of the expert’s testimony; such testimony must still
be assessed before it is presented to the jury.” Nease,
848 F.3d at 231 (quoting McClain v. Metabolife Int’l,
Inc., 401 F.3d 1233, 1238 (11th Cir. 2005) (emphasis
added)). Therefore, “[a]lthough the jury ultimately
decides the ‘weight’ of the evidence, the judge ensures
there is sufficient probative value ... to justify submitting the issue in the first instance.” Daniel D. Blinka,
Expert Testimony and the Relevancy Rule in the Age
of Daubert, 90 Marq. L. Rev. 173, 191 (2006). Here,
the issues presented to the court deal not only with
the validity of the underlying data used by Dr. Sahu
but also with Dr. Sahu’s methods in applying that data to the facts of the case. I will now proceed to Defendants’ arguments regarding relevance and reliability.
A. Relevance Challenge: The “Fit” of Dr. Sahu’s Opinions to the Facts of the Case
First, both UCC and Covestro argue that Dr. Sahu’s opinions are irrelevant or do not “fit” the facts of
the case, because this case deals solely with EtO
emissions from the Defendants’ operations at South
Charleston, and Dr. Sahu’s model consists of combined emissions sources from operations at both Institute and South Charleston. See [ECF No. 310, at
12]; [ECF No. 328, at 4]. According to UCC, this failure to disaggregate the emissions sources and resulting exposure estimates makes it “impossible to dis-
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cern the impacts of EtO emissions” from just the
South Charleston facility. [ECF No. 310, at 3]. And
Defendants argue that this same issue plagues the
jury’s ability to discern the alleged impacts from each
of their separate operations at that facility. As a result, Defendants claim that Dr. Sahu’s model and
opinions are irrelevant and should be excluded. Id. at
12; see [ECF No. 328 at 13 (“Dr. Sahu’s opinions are
irrelevant and unreliable because he does not ... separate alleged impacts between the defendants.”)].
Plaintiff, conversely, argues that while Dr. Sahu’s
model presents combined results from both Institute
and South Charleston, it is “entirely capable of
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