Stupp Corporation, Adivision of Stupp Bros., Inc., Ipsco Tubulars Inc., Maverick… v. United States

N OTE: This disposition is nonprecedential.
United States Court of Appeals
for the Federal Circuit
______________________
STUPP CORPORATION, A DIVISION OF STUPP
BROS., INC., IPSCO TUBULARS INC., MAVERICK
TUBE CORPORATION,
Plaintiffs
WELSPUN TUBULAR LLC USA,
Plaintiff-Appellee
v.
UNITED STATES,
Defendant-Appellee
HYUNDAI STEEL COMPANY,
Defendant
SEAH STEEL CORP.,
Defendant-Appellant
______________________
2023-1663
______________________
Appeal from the United States Court of International
Trade in Nos. 1:15-cv-00334-CRK, 1:15-cv-00336-CRK,
1:15-cv-00337-CRK, Judge Claire R. Kelly.
______________________
Decided: April 23, 2025
______________________
Case: 23-1663 Document: 117 Page: 1 Filed: 04/23/2025

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STUPP CORPORATION v. US 2
J EFFREY D AVID G ERRISH , Schagrin Associates, Wash-
ington, DC, argued for plaintiff-appellee. Also represented
by N ICHOLAS J. BIRCH , SAAD Y OUNUS CHALCHAL ,
CHRISTOPHER CLOUTIER, ELIZABETH D RAKE , WILLIAM
ALFRED F ENNELL , L UKE A. MEISNER , ROGER BRIAN
SCHAGRIN.
ROBERT R. K IEPURA , Commercial Litigation Branch,
Civil Division, United States Department of Justice, Wash-
ington, DC, argued for defendant-appellee. Also repre-
sented by CLAUDIA BURKE, P ATRICIA M. MCCARTHY ,
YAAKOV ROTH ; VANIA WANG, Office of the Chief Counsel for
Trade Enforcement and Compliance, United States De-
partment of Commerce, Washington, DC.
J EFFREY M. WINTON, Winton & Chapman PLLC, Wash-
ington, DC, argued for defendant-appellant. Also repre-
sented by MICHAEL J OHN CHAPMAN, VI MAI .
______________________
Before L OURIE, BRYSON, and STARK, Circuit Judges.
Additional views filed by Circuit Judge STARK.
STARK, Circuit Judge.
SeAH Steel Corporation (“SeAH”), a Korean manufac-
turer of welded line pipe, appeals the decision of the Court
of International Trade (“Trade Court”) sustaining the third
remand redetermination by the U.S. Department of Com-
merce (“Commerce”) in its 2015 less-than-fair-value
(“LTFV”) investigation of welded line pipe imported from
the Republic of Korea (“Korea”). The Trade Court judg-
ment affirmed Commerce’s assignment of a 2.53% anti-
dumping duty on SeAH’s imports. J.A. 3. Consistent with
our precedential opinion in Marmen Inc. v. United States
Wind Tower Trade Coalition, No. 23-1877 (“Marmen”), we
vacate and remand for Commerce to have an opportunity
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STUPP CORPORATION v. US 3
to “re-perform a differential pricing analysis” that “may not
rely on Cohen’s d test.” Slip Op. at 23.
I
The facts of this case are set out in detail in our earlier
decision, Stupp Corporation v. United States, 5 F.4th 1341,
1344-45, 1348 (Fed. Cir. 2021). A short summary suffices
for present purposes.
In the course of its LTFV investigation, Commerce de-
termined that SeAH engaged in targeted dumping; that is,
“a pattern of export prices (or constructed export prices) for
comparable merchandise that differ significantly among
purchasers, regions, or periods of time.” 19 U.S.C. § 1677f-
1(d)(1)(B). Such targeted dumping can be “masked,” and
go undetected – and, therefore, unaddressed by imposition
of an anti-dumping duty – “because a respondent’s sales of
low-priced dumped merchandise would be averaged with
(and offset by) sales of higher-priced masking merchandise,
giving the impression that no dumping was taking place.”
Stupp, 5 F.4th at 1345 (internal quotation marks omitted).
“To address the problem of targeted dumping, Congress
created an exception to the use of the average-to-average
[A-to-A] method” Commerce ordinarily uses “for calculat-
ing a dumping margin.” Id. “Commerce refers to the alter-
native method of calculating a weighted average dumping
margin as the ‘average-to-transaction’ [A-to-T] method.”
Id. Commerce sometimes also employs “some hybrid of the
two,” combining the average-to-average and average-to-
transaction methods. Marmen, Slip Op. at 16.
To “implement[] Congress’s directive” to uncover tar-
geted dumping, and determine whether to use the A-to-A,
A-to-T, or hybrid comparison methodology, Commerce uses
a “differential pricing analysis.” Stupp, 5 F.4th at 1346.
“The differential pricing analysis involves three tests . . . :
(1) Cohen’s d test, (2) the ratio test, and (3) the meaningful
difference test.” Marmen, Slip Op. at 16 n.2 (internal quo-
tation marks and citations omitted).
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STUPP CORPORATION v. US 4
This appeal is focused on the first of these steps, Co-
hen’s d test, which is “named after statistician Jacob Co-
hen” and is used “to evaluate whether the test group differs
significantly from the comparison group.” Stupp, 5 F.4th
at 1346. “If the Cohen’s d value is equal to or greater than
0.8 for any test group, the observations within that group
are said to have ‘passed’ the Cohen’s d test, i.e., Commerce
deems the sales prices in the test group to be significantly
different from the sales prices in the comparison group.”
Id. at 1347.
As we set out when this case was before us in 2021,
“Commerce applied its differential pricing analysis to
SeAH’s sales of welded line pipe and selected the hybrid
approach for calculating SeAH’s weighted average dump-
ing margin. That approach resulted in a weighted average
dumping margin of 2.53%.” Id. at 1348 (internal citations
omitted). After the Trade Court affirmed Commerce, SeAH
appealed to us and contended (as relevant here) that “Com-
merce misused the Cohen’s d test in its differential pricing
analysis,” because “the data in this case did not satisfy the
conditions required to achieve meaningful results from the
Cohen’s d test.” Id. at 1357. We “agree[d] that there are
significant concerns relating to Commerce’s application of
the Cohen’s d test in this case and, more generally, in ad-
judications in which the data groups being compared are
small, are not normally distributed, and have disparate
variances.” Id. We expressed concern, in particular, that
“Commerce’s application of the Cohen’s d test to data that
do not satisfy the assumptions on which the test is based
may undermine the usefulness of the interpretive cutoffs.”
Id. Therefore, we remanded “to give Commerce an oppor-
tunity to explain whether the limits on the use of the Co-
hen’s d test prescribed by Professor Cohen and other
authorities were satisfied in this case or whether those lim-
its need not be observed when Commerce uses the Cohen’s
d test in less-than-fair-value adjudications.” Id. at 1360.
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STUPP CORPORATION v. US 5
On remand, Commerce again applied its differential
pricing analysis, including Cohen’s d test, and concluded
that the “statistical criteria do not serve as a basis for Dr.
Cohen’s thresholds.” J.A. 37. Accordingly, in Commerce’s
view, Cohen’s d test can reasonably be used even when the
data being analyzed does not satisfy the three statistical
criteria about which we had raised concern in the earlier
appeal. SeAH again appealed to the Trade Court, which
determined that “Commerce has adequately explained how
its methodology,” including its use of Cohen’s d, “is reason-
able.” J.A. 27. SeAH timely appealed to us. We have ju-
risdiction pursuant to 28 U.S.C. § 1295(a)(5).
II
The Trade Court judgment we are reviewing sustained
Commerce’s imposition of a 2.53% anti-dumping duty on
SeAH. The Trade Court was persuaded that Commerce
had satisfactorily explained why it was reasonable to use
Cohen’s d test under circumstances in which the statistical
requirements for use of Cohen’s d are not met. Before us,
the government defends Commerce’s analysis and asks us
to agree with the Trade Court’s conclusion that limits on
the use of Cohen’s d “are only relevant as a matter of sta-
tistical significance, and do not apply when analyzing a
whole population.” Stupp Corp. v. United States, 619 F.
Supp. 3d 1314, 1323 (Ct. Int’l. Trade Feb. 24, 2023). The
government further argues that the second and third steps
of its differential pricing analysis, namely the ratio test and
meaningful difference test, “compensate for the . . . possible
inaccuracies” that may result from use of Cohen’s d on data
not meeting the statistical requirements of that test. Gov’t
Br. at 13.
The problem for the government is that it made these
precise arguments in Marmen and we rejected them. In
particular, in Marmen we held it is “unreasonable for Com-
merce to use Cohen’s d as part of its differential pricing
analysis when the test is applied to data sets that do not
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STUPP CORPORATION v. US 6
satisfy the statistical assumptions” on which Cohen’s d is
predicated. Slip Op. at 19. The three “required assump-
tions” for Cohen’s d are “normal distributions, equal varia-
bility, and equal and sufficiently numerous data.” Id. at
15. There was “no dispute that Marmen’s data does not
satisfy these assumptions” and, therefore, we held, “Co-
hen’s d cannot be used . . . to determine ‘a pattern of export
prices (or constructed export prices) for comparable mer-
chandise that differ significantly among purchaser, re-
gions, or periods of time.” Id. (quoting 19 U.S.C. § 1677f-
1(d)(1)(B)).
We confront the very same situation here, and we are
compelled to reach the same result. Here, as in Marmen,
it is undisputed that SeAH’s U.S. pricing data fails to sat-
isfy the statistical assumptions necessary to permit a rea-
sonable application of Cohen’s d in a differential pricing
analysis: “normal distributions, equal variability, and
equal and sufficiently numerous data.” Slip Op. at 15.
Commerce’s assertion that these assumptions “need not be
observed,” Gov’t Br. at 14, 16 n.5, is no longer a tenable
position (if it ever was). Accordingly, we hold that it was
unreasonable for Commerce to use Cohen’s d as part of its
differential pricing analysis in this case. We vacate the
judgment of the Trade Court and remand for that court to
remand to Commerce, which may re-perform a differential
pricing analysis without relying on Cohen’s d. 1
1 We reject SeAH’s request that we instruct Com-
merce to apply the average-to-average comparison method-
ology and its resulting 1.97% margin, which would be
considered de minimis and, therefore, result in no duty be-
ing imposed. On remand, Commerce has discretion to do
as SeAH wishes, but it also has the opportunity, if it pre-
fers, to re-perform a differential pricing analysis without
using Cohen’s d, which may result in the use of the aver-
age-to-transaction comparison or a hybrid methodology.
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STUPP CORPORATION v. US 7
III
We have considered the government’s remaining argu-
ments and find them unpersuasive. Thus, we vacate and
remand for proceedings consistent with this opinion.
VACATED AND REMANDED
COSTS
Costs to SeAH.
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N OTE: This disposition is nonprecedential.
United States Court of Appeals
for the Federal Circuit
______________________
STUPP CORPORATION, A DIVISION OF STUPP
BROS., INC., IPSCO TUBULARS INC., MAVERICK
TUBE CORPORATION,
Plaintiffs
WELSPUN TUBULAR LLC USA,
Plaintiff-Appellee
v.
UNITED STATES,
Defendant-Appellee
HYUNDAI STEEL COMPANY,
Defendant
SEAH STEEL CORP.,
Defendant-Appellant
______________________
2023-1663
______________________
Appeal from the United States Court of International
Trade in Nos. 1:15-cv-00334-CRK, 1:15-cv-00336-CRK,
1:15-cv-00337-CRK, Judge Claire R. Kelly.
______________________
STARK, Circuit Judge, additional views.
Case: 23-1663 Document: 117 Page: 8 Filed: 04/23/2025

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STUPP CORPORATION v. US 2
Were we writing on a blank slate, I might well be per-
suaded by Commerce that its use of Cohen’s d test, as one
step in its three-step differential pricing analysis, is
reasonable. See generally Stupp, 5 F.4th at 1353 (“Our
precedents make clear that the relevant standard for
reviewing Commerce’s selection of statistical tests and
numerical cutoffs is reasonableness . . . .”). Moreover, had
Commerce not labelled what it is doing at step one as
“Cohen’s d,” and had it not tried to borrow credibility for
its test by reference to Dr. Cohen’s extensive work and
other literature endorsing Cohen’s d, I might agree it
should be permitted to use something quite like Cohen’s d
as a rough, initial “measur[e] [of] the practical signifi-
cance of price difference[s].” Gov’t Br. at 17. After all,
Commerce has expertise we lack and broad discretion to
decide how to perform its statutory duty to identify tar-
geted dumping. See id. at 1346 (“Congress has not delin-
eated exactly how Commerce is to assess whether there is
a pattern of export prices . . . differ[ing] significantly
among purchasers, regions, or periods of time, or how
Commerce is to explain[] why such differences cannot be
taken into account using the average-to-average or trans-
action-to-transaction methods.”) (internal quotation
marks omitted; alterations in original).
But, of course, we are not addressing a question of
first impression. Quite the contrary. Marmen preceden-
tially holds it is “unreasonable” for Commerce to use
Cohen’s d when the three assumptions underlying it –
“normal distributions, equal variability, and equal and
sufficiently numerous data” – are not satisfied. Slip Op.
at 23. Additionally, the Court remanded this very case
nearly four years ago to give Commerce an opportunity to
explain why meeting these assumptions is not necessary
and, as Marmen well and thoroughly describes, Com-
merce did not do so in a particularly persuasive manner.
See id. at 15-23. And this case does not call on us to
assess the broader question of whether Commerce can
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STUPP CORPORATION v. US 3
ever reasonably rely on rules of thumb that are not statis-
tically grounded.
Thus, I entirely agree with my colleagues that we
must vacate the judgment of the Court of International
Trade and instruct it to remand to Commerce, which may
choose to re-perform a differential price analysis without
using Cohen’s d.
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