In the

       United States Court of Appeals
                     For the Seventh Circuit
                         ____________________
No. 17-1990
CHERYL DALTON,
                                                      Plaintiff-Appellant,

                                      v.

TEVA NORTH AMERICA, et al.,
                                                   Defendants-Appellees.
                         ____________________

            Appeal from the United States District Court for the
             Southern District of Indiana, Evansville Division.
              No. 3:15-cv-00162 — Richard L. Young, Judge.
                         ____________________

       ARGUED FEBRUARY 13, 2018 — DECIDED JUNE 4, 2018
                         ____________________

   Before SYKES and BARRETT, Circuit Judges, and GRIESBACH,
Chief District Judge. *
   BARRETT, Circuit Judge. Cheryl Dalton appeals the sum-
mary judgment entered against her in this products liability
case. The district court held that Dalton’s claims failed under
Indiana law because she did not provide expert evidence on


   *   Of the Eastern District of Wisconsin, sitting by designation.
2                                                    No. 17-1990

the issue of causation. Dalton contends that she did not have
to provide expert evidence because the cause of her injuries
would be readily apparent to a lay juror. Because the district
court correctly applied Indiana law, we affirm.
                                I.
    In 2007, Dalton’s doctor implanted a ParaGard Intrauter-
ine Device (“IUD”) in her uterus. An IUD is a form of long-
term birth control, and the one Dalton used is manufactured,
marketed, and distributed by a group of corporate affiliates
whom we will collectively call “Teva.” It is not clear what
role each of those corporate affiliates plays in relation to this
IUD, but this appeal does not require us to sort that out.
    Dalton became dissatisfied with the IUD in 2013 and
asked her doctor to remove it. The doctor did so by grasping
the IUD’s strings with a ring forcep and pulling the IUD
down. The procedure, however, removed only part of the
IUD. A piece had broken off either before or during the re-
moval, and that piece was now lodged in her uterus. Dal-
ton’s doctor advised her that removing the remaining por-
tion of the IUD would require a hysterectomy.
    Dalton sued Teva in federal court. She asserted three
products liability claims, which she styled as “strict liability,”
“strict products liability failure to warn,” and “manufactur-
er’s defect.” Under the case-management plan submitted by
the parties and adopted by the district court, Dalton had un-
til November 18th to disclose any expert witness and serve
the expert witness report required by Federal Rule of Civil
Procedure 26(a)(2). When Dalton made no expert disclo-
sures, Teva moved for summary judgment. It argued that
Indiana law requires expert testimony to show causation in
No. 17-1990                                                       3

products liability actions, and Dalton’s failure to procure any
meant that she could not prove an essential element of her
claims. Dalton responded that the causation issue was so
straightforward that expert testimony was unnecessary. The
district court granted summary judgment to Teva.
                                II.
    It has been a struggle to get the information we need to
determine whether subject matter jurisdiction exists in this
case. Because the claims in this suit arise under state law,
Dalton relied on the diversity jurisdiction statute, 28 U.S.C.
§ 1332, to bring her case in federal court. That statute re-
quires complete diversity among the parties, and proving
the citizenship of each party is Dalton’s burden. 1 Craig v. On-
tario Corp., 

, 876 (7th Cir. 2008). There is no prob-
lem with the five defendants whom Dalton sued under the
name “John Doe.” Those defendants were nominal parties
who served as placeholders in the event that Dalton found
additional people to sue, and we have held that the citizen-
ship of such defendants can be disregarded for diversity ju-
risdiction. Moore v. Gen. Motors Pension Plans, 

, 850
(7th Cir. 1996). But Dalton must establish the citizenship of
the eight other defendants who are purportedly within the
Teva corporate family—Teva Pharmaceuticals USA Inc., Teva
Neuroscience Inc., Teva Women’s Health LLC, and so on.
   Dalton’s complaint did not allege the citizenship of these
defendants. It asserted that the defendants as a group “are
incorporated and have their headquarters in the state of
Pennsylvania or another state different from the Plaintiff.”

   1 Dalton’s complaint satisfied the amount-in-controversy require-
ment because it sought more than $75,000 in damages.
4                                                 No. 17-1990

But a complaint may not merely allege diversity of citizen-
ship without identifying the defendants’ states of citizenship,
McCready v. eBay, Inc., 

, 890–91 (7th Cir. 2006),
and it is difficult to perceive any material difference between
that practice and the bare assertion that the defendants are
citizens of “another state different from the Plaintiff.” And
even if we assume that all eight named defendants are cor-
porations, what matters for the citizenship of a corporation
is its state of incorporation and its principal place of busi-
ness, not its “headquarters.” Hertz Corp. v. Friend, 

, 93 (2010). Unfortunately, the citizenship of the Teva de-
fendants was never clarified in the district court.
    Dalton’s opening brief on appeal was similarly deficient.
In any case premised upon diversity jurisdiction, Circuit
Rule 28(a)(1) requires the appellant to include a jurisdiction-
al statement identifying “the jurisdictional amount and the
citizenship of each party to the litigation.” Even though we
have clearly stated that “an appellant’s naked declaration
that there is diversity of citizenship is never sufficient,”
Thomas v. Guardsmark, LLC, 

, 533 (7th Cir. 2007),
Dalton stated only that the case “involves a diversity of citi-
zenship.” After we ordered her to file a new jurisdictional
statement, she asserted her own citizenship (Indiana), the
citizenship of three corporate defendants (Pennsylvania),
and the fact that two other corporate defendants were just
prior names of those three Pennsylvania citizens. Teva’s brief
clarified that the three Pennsylvania citizens identified by
Dalton are actually citizens of both Pennsylvania and Dela-
ware. But rather than stating the citizenship of the remaining
three defendants, Teva merely asserted that they were never
served and did not appear in the district court. That may be,
but because those parties were not dismissed from the case,
No. 17-1990                                                   5

we must still account for their citizenship. By failing to ad-
dress it, Teva violated Circuit Rule 28, which obligates an
appellee to provide a complete and correct jurisdictional
statement when the appellant’s statement falls short.
   We raised these problems at oral argument, and in post-
argument supplemental briefing, the parties finally account-
ed for the three remaining defendants. We now know that
one unserved defendant is just the past name of another un-
served defendant, who is a citizen of Delaware and Kansas,
and that the final unserved defendant does not exist and has
never existed. Having confirmed that no defendant is a citi-
zen of Indiana, we are finally able to conclude that subject-
matter jurisdiction exists. It should not have taken us two
rounds of jurisdictional statements, oral argument, and sup-
plemental briefing to extract this basic information from the
parties.
                              III.
    Dalton’s claims arise under the Indiana Products Liability
Act, which governs all consumer actions against a manufac-
turer for physical harm caused by a product, “regardless of
the substantive legal theory or theories upon which the ac-
tion is brought.” Ford Motor Co. v. Rushford, 

,
809 (Ind. 2007) (quoting IND. CODE § 34-20-1-1); see also Piltch
v. Ford Motor Co., 

, 632 (7th Cir. 2015) (applying
the Indiana Products Liability Act to claims alleging “a de-
sign defect, a manufacturing defect, or a failure to warn”).
Under any of those theories, she must prove that her injury
was proximately caused by whatever defect or breach of du-
ty underlies her claim. Id.; see also 

. Dalton lost below because, believing it was unnecessary,
she chose not to rely on expert testimony to prove the causa-
6                                                   No. 17-1990

tion element in this case. Whether she is right about that de-
pends on what the Indiana Products Liability Act requires.
   The Act insists upon expert testimony when an issue “is
not within the understanding of a lay person.” 

. Causation is often such an issue. See, e.g., 

U-Haul Int’l, Inc. v. Nulls Mach. & Mfg. Shop, 

, 285 n.3 (Ind. Ct. App. 2000); Daub v. Daub, 

, 877–78 (Ind. Ct. App. 1994). If the circumstantial evi-
dence in a case would require a lay juror to engage in “pure
speculation” to find causation, then expert evidence is neces-
sary under Indiana law. 

.
   Dalton contends that “proximate cause is obvious” in this
case because it involves “uncomplicated facts that lead to
only on[e] conclusion.” In Dalton’s view, a juror could look
at a broken IUD and plainly see that some error of Teva’s
caused the break. But as the district court held, that is exactly
the sort of speculation that is insufficient to sustain a prod-
ucts liability action under the Indiana law. Dalton provides
no explanation for how a lay juror faced with a broken IUD
could identify the cause of the break—maybe the IUD was
damaged after coming into the possession of the physician,
maybe human error resulted in damage or some other prob-
lem during implantation or removal, or maybe there’s an-
other explanation entirely.
    This case is far removed from situations in which a cau-
sation issue is so obvious that a plaintiff may forgo expert
testimony. See, e.g., Higgins v. Koch Dev. Corp., 

,
702 (7th Cir. 2015) (“[W]hen a plaintiff suffers from a broken
leg or a gash when hit by a vehicle, he doesn’t need to pro-
duce expert testimony.” (quoting Myers v. Ill. Cent. R.R. Co.,

, 643 (7th Cir. 2010)). It is far more like Piltch, a
No. 17-1990                                                   7

products liability case in which we held that a similarly
sparse set of facts was insufficient to override the need for
expert evidence to show defect and causation. There, the
plaintiffs suffered serious injuries when their SUV crashed.

. They contended that a manufacturing
or design defect had prevented their airbags from deploying,
which increased the severity of their injuries. 

plaintiffs designated no expert witness; instead, they chose
to rely on their experience in the accident and the owner
manual’s statement that the airbags were supposed to de-
ploy in a crash. 

that the plaintiffs could not show
the existence of a design defect without having an expert
witness testify about potential alternative designs, and they
could not show the existence of a manufacturing defect
without expert testimony (or some other, more persuasive
circumstantial evidence) showing that the airbags as de-
signed should have deployed in the crash. 

    Just as in Piltch, a judgment for the plaintiff in this case
would require the jurors to speculate about the existence of a
defect, the reason for the proven defect, and that the proven
defect caused the break. Contrary to Dalton’s contention, the
issue of causation in her case is not obvious. The district
court was therefore correct to hold that Dalton could not
prove her tort claims without expert testimony.
                              IV.
    Dalton’s remaining argument is difficult to parse. She
appears to contend that even if expert testimony is necessary
on her manufacturing-defect claim, it is unnecessary on her
claims that are denominated as “strict liability” and “failure
to warn.” Her argument on this point is only one sentence,
8                                                  No. 17-1990

and inadequately briefed arguments are forfeited. See Puffer
v. Allstate Ins. Co., 

, 718 (7th Cir. 2012).
    Dalton shifts gears in her reply brief. This argument is al-
so unclear, but she seems to fault the district court’s opinion
for failing to address why it was entering summary judg-
ment on her failure-to-warn and strict-liability claims. She
has misunderstood the district court’s opinion. The court
discussed Dalton’s wholesale failure to provide evidence of
causation, and all of her claims require proof of causation.
Kovach v. Caligor Midwest, 

, 199 (Ind. 2009)
(holding that a plaintiff in a failure-to-warn case must estab-
lish causation); 

(“[W]ith respect
to strict liability actions, the plaintiff must prove that … the
defective condition was the proximate cause of the plaintiff’s
injuries.”). Even if we were to consider an argument raised
for the first time in a reply brief, there would be no cause for
second-guessing here.
    The district court’s judgment is AFFIRMED.