                                In the

       United States Court of Appeals
                  For the Seventh Circuit
                      ____________________
No. 14-3448
C.W. and E.W., by Guardians and Next Friends
ADELE A. WOOD and JASON A. WOOD,
                                       Plaintiffs-Appellants,

                                   v.

TEXTRON, INC.,
                                                  Defendant-Appellee.
                      ____________________

          Appeal from the United States District Court for the
          Northern District of Indiana, South Bend Division.
            No. 3:10 CV 87 — Philip P. Simon, Chief Judge.
                      ____________________

       ARGUED MAY 18, 2015 — DECIDED AUGUST 26, 2015
                  ____________________

   Before KANNE and SYKES, Circuit Judges, and Ellis, District
Judge.*
    KANNE, Circuit Judge. Government regulators and scien-
tists agree: exposure to vinyl chloride poses serious health

*TheHonorable Sara L. Ellis, of the United States District Court for the
Northern District of Illinois, sitting by designation.
2                                                            No. 14-3448

risks to humans. Vinyl chloride is a known carcinogen, mu-
tagen, and genotoxin.1 But in what quantity and for how
long must a human—in this case, two infant children—be
exposed to vinyl chloride before those health risks material-
ize? The experts for C.W. and E.W., the minor children of Ja-
son and Adele Wood, attempted to answer these difficult
questions in this toxic-tort case.
    Unfortunately for the Woods, their attempts fell short.
The district court excluded each of the appellants’ experts,
observing they did not use reliable bases to support their
opinions. Having excluded the appellants’ experts, the dis-
trict court then granted summary judgment in favor of Tex-
tron. It found that, without the experts’ opinions, the appel-
lants could not prove general and specific causation—
required elements under Indiana law in a toxic-tort case.
Although we disagree with the district court’s rationale re-
garding causation, we nevertheless affirm.
                           I. BACKGROUND
    A. Preliminary History
   Textron began operations at its fastener manufacturing
plant in Rochester, Indiana, in 1954. The Torx plant, as it
came to be known, proved to be successful; it remained in
operation through 2006. During its operations, however, the


1 For the sake of clarity (primarily our own), we define scientific terms as
the need arises. This occasion presents such a need. In reverse order: a
genotoxin is a poisonous substance that damages DNA; a mutagen is
something that is capable of causing mutations to DNA; and a carcino-
gen is something that causes cancer. MedicineNet.com Home Page, avail-
able at search.medicinenet.com (last visited Aug. 5, 2015).
No. 14-3448                                                       3

plant released vinyl chloride—a toxic gas. That vinyl chlo-
ride eventually seeped into the ground water, contaminating
nearby residential wells.
   One of those wells belonged to the Woods. Both Textron
and the Indiana Department of Environmental Management
performed testing on the Woods’ well. Their tests revealed
varying levels of vinyl chloride—from 5.00 and 8.40 parts
per billion to 8.60 and 9.00 parts per billion.2
    Once the Woods learned that this toxic substance had
contaminated their well, they understandably left immedi-
ately. Jason and Adele believed the health risks to their chil-
dren were simply too high to remain at the Rochester house.
But in the Woods’ opinion, there was more at stake than the
future risk of cancer; there was the present risk of illness.
While living at the Rochester house, C.W. and E.W. experi-
enced gastrointestinal issues (vomiting, bloody stools), im-
munological issues, and neurological issues.
   The Woods adopted their son, C.W., when he was eleven
weeks old. He came home on May 11, 2007. The Woods
adopted their daughter, E.W., when she was eleven days old.
She came home on April 25, 2008. Both children were
younger than two years old when the entire family left the
Rochester house in November 2008. Their illnesses coincided
with their time spent in that house.
   After the Woods moved from that house, C.W.’s and
E.W.’s health improved. But the parents’ concerns did not
abate. Fearful that vinyl chloride caused C.W.’s and E.W.’s

2The appellants’ experts later estimated that C.W. and E.W. ingested
water contaminated by vinyl chloride at 3 parts per billion.
4                                                    No. 14-3448

conditions (and mindful of the known cancer risks), Jason
and Adele sued Textron on behalf of their children in Fulton
County Circuit Court. There, they advanced a three-count
complaint, alleging negligence, negligence per se, and negli-
gent infliction of emotional distress.3 The crux of these Indi-
ana tort-law claims was that Textron exposed C.W. and E.W.
to vinyl chloride, which caused their illnesses and substan-
tially increased their risk of cancer and other adverse health
effects. Just one week after the filing of the complaint, Tex-
tron successfully removed the case to federal court. 28 U.S.C.
§§ 1332, 1441, 1446. The appellants then filed a Second
Amended Complaint, this time in federal court, to add a
fourth count for willful and wanton misconduct.
    The case proceeded through discovery and the marshal-
ing of experts until, nearly four years after the appellants
filed their original complaint, Textron filed a motion in
limine to exclude the appellants’ three expert witnesses. As
we noted above, that motion was successful; the district
court granted it in its entirety. The district court then found
that, without the experts, the appellants could not prove
general or specific causation. It granted summary judgment
in favor of Textron on all of the appellants’ claims.
    Before we turn our attention to the experts, we note that
there are a number of contested facts that are not at issue in
this appeal. For example, this appeal is not about whether, or
with what frequency, Jason and Adele used bottled instead
of tap water to make formula for their infant children. Nor is


3 In their Second Amended Complaint, the appellants added a fourth
count for willful and wanton misconduct.
No. 14-3448                                                     5

this appeal about whether Jason and Adele’s reverse-
osmosis-water-filtration system sufficiently guarded the
children against unacceptable levels of vinyl chloride.
    Instead, this appeal is about whether the district court
abused its discretion in excluding the appellants’ experts
based on the reliability of their methodology, and if it did not
abuse its discretion, whether we should affirm its grant of
summary judgment in favor of Textron. See Anderson v. Liber-
ty Lobby, Inc., 477 U.S. 242, 248 (1986) (“Only disputes over
facts that might affect the outcome of the suit under govern-
ing law will properly preclude the entry of summary judg-
ment.”).
   B. The Experts
    Because our jurisdiction is based on diversity of citizen-
ship, we apply federal procedural law and state substantive
law. Allen v. Cedar Real Estate Grp., LLP, 236 F.3d 374, 380 (7th
Cir. 2001) (citing Erie R.R. v. Tompkins, 304 U.S. 64, 78 (1938)).
The parties do not dispute that Indiana substantive law ap-
plies here. To prove their toxic-tort claims under Indiana law,
the appellants needed to present evidence of general and
specific causation. 7-Eleven, Inc. v. Bowens, 857 N.E.2d 382,
389 (Ind. Ct. App. 2006). General causation examines wheth-
er the substance—in this case, vinyl chloride—“had the ca-
pacity to cause the harm alleged[.]” Id. (emphasis added).
Specific causation, by contrast, examines whether the sub-
stance did, in fact, cause the harm alleged. Id. (emphasis
added). To satisfy this bifurcated burden, the plaintiffs of-
fered the testimony of three experts: (1) Dr. James G.
Dahlgren; (2) Dr. Vera S. Byers; and (3) Dr. Jill E. Ryer-
Powder.
6                                                             No. 14-3448

    Both parties agree that these experts are well-qualified.
So we can set that issue to the side. The dispute before us
concerns the reliability of the methodology they employed in
generating their expert opinions. The following section high-
lights their methodology as well as the district court’s ra-
tionale in rejecting it. We begin with Dr. Dahlgren.
        1. Dr. James G. Dahlgren
    Dr. Dahlgren offered opinions on both general and spe-
cific causation, testifying that, in his judgment, vinyl chlo-
ride can cause and did cause the children’s illnesses. He also
opined that it is highly likely that both children will develop
cancer at some point in the future. He based these opinions
on a differential etiology4 and the fact that levels of vinyl
chloride detected in the appellants’ water supply exceeded
the regulatory levels set by the United States Environmental
Protection Agency (“EPA”) and the Indiana Department of
Environmental Management, among other government
agencies. Dr. Dahlgren also based his opinions on timing, or
in his words, “temporality.” In his view, the fact that the ap-
pellants’ symptoms began after exposure to vinyl chloride

4 “Etiology is the study of causation.” Myers v. Ill. Cent. R.R. Co., 629 F.3d
639, 644 (7th Cir. 2010) (citations omitted). A differential etiology is a
process-of-elimination approach to determining a subject’s cause of inju-
ry. Under this method, an expert “considers all relevant potential causes
of the symptoms and then eliminates alternative causes.” Federal Judicial
Center, Reference Manual on Scientific Evidence 214 (1994). Although the
parties and the district court below refer to this method as a “differential
diagnosis,” that term is really a misnomer. A “diagnosis” is concerned
only about naming the condition or ailment, not establishing its cause.
Id.; see also Happel v. Walmart Stores, Inc., 602 F.3d 820, 825 n.7 (7th Cir.
2010).
No. 14-3448                                                      7

and lessened after removal helps demonstrate that vinyl
chloride is the cause.
    As for Dr. Dahlgren’s differential etiology, it is largely
based on the findings (or lack thereof) of other doctors who
have examined C.W. and E.W. To be sure, Dr. Dahlgren con-
ducted physical examinations of both C.W. and E.W. He also
reviewed their medical records. But his differential etiology
is silent on these matters. According to Dr. Dahlgren, “[t]he
scientific studies … demonstrate that damage to the immune
system and the nervous system are known to be caused by
[vinyl chloride] exposure. The thorough evaluations by the chil-
drens’ [sic] doctors have not found an alternative explanation … .”
(emphasis added).
    Thus, to accept Dr. Dahlgren’s approach to differential
etiology, one must accept both the scientific studies upon
which Dr. Dahlgren relied and the care taken by the doctors
who examined C.W. and E.W. One must also accept that vi-
nyl chloride should be ruled in as a possible cause at all—a
point we address below.
    The district court found Dr. Dahlgren’s methodology to
be unreliable. Citing Cunningham v. Masterwear Corp., 569
F.3d 673, 674–75 (7th Cir. 2009), it first found that Dr.
Dahlgren could not rely on regulatory exceedances to
demonstrate causation. Second, the district court found that
Dr. Dahlgren failed to connect the dots between the scientific
studies that he analyzed and the opinions that he offered.
This is a Joiner problem. In Gen. Elec. v. Joiner, 522 U.S. 136,
138 (1997), the Supreme Court decided to apply the abuse of
discretion standard in reviewing the admission or exclusion
of expert testimony. Affirming the district court’s exclusion
of the experts there, the Court held that “nothing in either
8                                                  No. 14-3448

Daubert or the Federal Rules of Evidence requires a district
court to admit opinion evidence which is connected to exist-
ing data only by the ipse dixit of the expert. A court may con-
clude that there is simply too great an analytical gap be-
tween the data and the opinion proffered.” Id. at 146 (cita-
tions omitted).
    In the case before us, the district judge found fault in the
studies that Dr. Dahlgren relied upon. “These articles … fail
to establish that [vinyl chloride] at the dose and duration
present in this case could cause the problems that the
[p]laintiffs have experienced or claim that they are likely to
experience.” C.W. v. Textron, 2014 U.S. Dist. LEXIS 34938, at
*53 (N.D. Ind. Mar. 17, 2014) (“Textron I”). The district judge
then rejected Dr. Dahlgren’s efforts to apply those studies to
this case. Id. at *45 (“The problem again, however, is that …
Dahlgren fails to bridge [the] gap by explaining how he is
able to extrapolate” from those studies).
       2. Dr. Vera S. Byers
   Like Dr. Dahlgren, Dr. Byers also offered opinions on
both general and specific causation. In her view, exposure to
vinyl chloride can cause and did cause the children’s illnesses.
She traced the children’s exposure to vinyl chloride to their
ingestion of contaminated drinking water, inhalation of va-
pors from bathing, and dermal contact. She then linked that
exposure to their gastrointestinal and immune-system prob-
lems. “The GI problems suffered by both children,” Dr.
Byers wrote, “are consistent with the adverse events associ-
ated with vinyl chloride exposure.” As for the appellants’
immune-system issues, she noted that C.W. and E.W. have a
“very similar pattern of elevated … immune complexes … .
Given that these two children are genetically unrelated, the
No. 14-3448                                                                9

most probable cause of this acquired immune complex com-
plement activation is the Vinyl Chloride exposure.” Dr.
Byers admitted that she knew little about C.W.’s and E.W.’s
family medical histories. She further opined that both chil-
dren are now at a heightened risk level for developing can-
cer.
   Like Dr. Dahlgren, Dr. Byers based her opinion, in part,
on a differential etiology. For E.W., Dr. Byers ruled in:
                  Congenital structural abnormalities
                  Infectious agents including viral
                  Degenerative
                  Neoplastic
                  Toxicity including allergies or in this case exposure
                   to vinyl chloride
                  Metabolic disorders
                  Psycho-social issues
She then ruled out each alternative explanation until siding
with vinyl chloride as the specific cause.5 To buttress her
conclusion, Dr. Byers also relied on timing. “Vinyl Chloride
exposure is the most probable cause of [E.W.’s] acute symp-
toms[,]” she opined. “Both children suffered these symp-
toms, most seriously by [E.W.], and both childrens’ [sic]
symptoms subsided when the exposure ceased.”
    Once again, to accept Dr. Byers’s approach, one must ac-
cept as relevant the scientific studies upon which Dr. Byers
relied. One must also accept that vinyl chloride should be

5   Dr. Byers’s report does not discuss a differential etiology for C.W.
10                                                 No. 14-3448

ruled in as a possible cause in the first place. The district
court accepted neither. It excluded Dr. Byers based on her
attenuated studies and on her failure to adequately extrapo-
late from them.
       3. Dr. Jill E. Ryer-Powder
    That brings us to Dr. Ryer-Powder. In her initial report of
August 17, 2011, she addressed the issue of general causa-
tion. Dr. Ryer-Powder claimed that the children’s exposure to
vinyl chloride was “at levels sufficient to cause harm” dur-
ing the applicable time period. She further claimed that this
same level of exposure was “sufficient to present an unac-
ceptable risk of cancer in the future.” Like Dr. Byers, she tied
the appellants’ exposure to ingestion, inhalation, and dermal
contact with vinyl chloride.
    For largely the same reasons the district court excluded
the testimony of Doctors Dahlgren and Byers, the district
court also excluded the testimony of Dr. Ryer-Powder. For
example, Dr. Ryer-Powder relied on regulatory exceedances
to formulate her opinion as to causation: “One means by
which the health risks from exposures to chemicals can be
assessed is by comparison to government standards and
regulations.” She found that in this case, the Woods’ drink-
ing water exceeded the standards set by relevant govern-
ment agencies. So in her view, that meant vinyl chloride was
within the realm of possible causes for the appellants’ inju-
ries.
   Dr. Ryer-Powder also relied on attenuated studies con-
cerning much higher exposure levels of vinyl chloride than
the ones experienced here. As with Doctors Dahlgren and
Byers, the district court found that she did not do the neces-
No. 14-3448                                                       11

sary work of extrapolating from those studies to C.W. and
E.W. In sum, the district court found that Dr. Ryer-Powder
did not offer a reliable basis to support her proffered opin-
ion.
   With this overview in mind, we turn to the merits.
                           II. ANALYSIS
   A. Principles of Law
      1. Admissibility of Expert Testimony
    Federal Rule of Evidence 702 and Daubert v. Merrell Dow
Pharmaceuticals., Inc., 509 U.S. 579 (1993), govern the admis-
sion of expert testimony in federal courts, even when our ju-
risdiction rests on diversity. See Wallace v. McGlothan, 606
F.3d 410, 419 (7th Cir. 2010) (holding “standards for admit-
ting expert evidence” are “matters that fall on the procedural
side of the Erie divide,” and are thus governed by federal
law) (citations omitted). Daubert itself commenced as a state
court action before it was removed to the Southern District
of California on diversity grounds. 509 U.S. at 582.
   Rule 702 provides:
      A witness who is qualified as an expert by
      knowledge, skill, experience, training, or education
      may testify in the form of an opinion or otherwise
      if: (a) the expert’s scientific, technical, or other spe-
      cialized knowledge will help the trier of fact to un-
      derstand the evidence or to determine a fact in is-
      sue; (b) the testimony is based on sufficient facts or
      data; (c) the testimony is the product of reliable
      principles and methods; and (d) the expert has reli-
      ably applied the principles and methods to the facts
      of the case.
12                                                           No. 14-3448

Fed. R. Evid. 702. Under this rule, expert testimony must not
only assist the trier of fact. It must also demonstrate suffi-
cient reliability—a key concern of the district court below. Id.
    The district court is the gatekeeper of expert testimony.6
We stress that “the key to the gate is not the ultimate cor-
rectness of the expert’s conclusions. Instead, it is the sound-
ness and care with which the expert arrived at her opin-
ion[.]”Schultz v. Akzo Nobel Paints, LLC, 721 F.3d 426, 431 (7th
Cir. 2013) (citations omitted).
    Daubert provides several guideposts for determining reli-
ability. These guideposts examine (1) whether the scientific
theory has been or can be tested; (2) whether the theory has
been subjected to peer-review and/or academic publication;
(3) whether the theory has a known rate of error; and (4)
whether the theory is generally accepted in the relevant sci-
entific community. Schultz v. Akzo Nobel Paints, LLC, 721 F.3d
426, 431 (7th Cir. 2013) (citing Daubert, 509 U.S. at 593–94).
    Importantly, this list is neither exhaustive nor mandatory.
Chapman v. Maytag Corp. (In re Chapman), 297 F.3d 682, 687
(7th Cir. 2002). In some cases it may also be appropriate to
examine, as the district court did here, whether there is “too
great an analytical gap between the data and the opinion
proffered.” Joiner, 522 U.S. at 146. Ultimately, reliability is
determined on a case-by-case basis. Ervin v. Johnson & John-
son, 492 F.3d 901, 904 (7th Cir. 2007).


6 We stress that “the key to the gate is not the ultimate correctness of the
expert’s conclusions. Instead, it is the soundness and care with which the
expert arrived at her opinion[.]”Schultz v. Akzo Nobel Paints, LLC, 721
F.3d 426, 431 (7th Cir. 2013) (citations omitted).
No. 14-3448                                                   13

       2. Standard of Review
    We employ a two-step standard of review in cases chal-
lenging a district court’s admission or exclusion of the testi-
mony of an expert. First, we review de novo a district court’s
application of the Daubert framework. United States v. Brum-
ley, 217 F.3d 905, 911 (7th Cir. 2000). If the district court
properly adhered to the Daubert framework, then we review
its decision to exclude (or not to exclude) expert testimony
for abuse of discretion. Id. (citing Walker v. Soo Line R.R. Co.,
208 F.3d 581, 590 (7th Cir. 2000)).
   B. The District Court’s Adherence to Daubert
    The district court properly adhered to the Daubert
framework. The court began its exhaustive review of the ap-
pellants’ three proposed experts by accurately outlining the
Daubert framework. Textron I, 2014 U.S. Dist. LEXIS 34938, at
*6–10. During that outline, the court aptly noted the need for
flexibility in applying Daubert, particularly given “the vari-
ous types of potentially appropriate expert testimony.” Id. at
*9 (citing Deputy v. Lehman Bros., Inc., 345 F.3d 494, 505 (7th
Cir. 2003)) (additional citations omitted).
    The court then conducted an in-depth review of the rele-
vant studies that the experts relied upon to generate their
differential etiology. Textron, supra, at *11–53. This careful
approach stands in stark contrast to other cases where we
concluded that courts did not adhere to the Daubert frame-
work. See, e.g., Metavante Corp. v. Emigrant Sav. Bank, 619 F.3d
748, 760 (7th Cir. 2010) (declining to apply abuse of discre-
tion standard where the district court’s one-sentence expert
determination did not satisfy Daubert); Naeem v. McKesson
Drug Co., 444 F.3d 593, 608 (7th Cir. 2006) (same). And on a
14                                                      No. 14-3448

much larger scale, the district court’s approach follows the
same path blazed by the Supreme Court in Joiner. 522 U.S. at
145 (reviewing four epidemiological studies advanced by the
respondent in support of the experts’ conclusions).
    According to the appellants, however, the district court
imposed an unachievable requirement that “published liter-
ature exist on the topic of vinyl chloride poisoning in small
children.” It did so, allegedly, despite the Supreme Court’s
admonition that “[p]ublication (which is but one element of
peer review) is not a sine qua non of admissibility.” Daubert,
509 U.S. at 593. The argument that the district court errone-
ously inflated the importance of publications is unavailing.
    The appellants misread the district court’s decision. The
district court imposed no such requirement. Instead, it fault-
ed the appellants’ experts for failing to adequately extrapo-
late from the studies they had. To be sure, the district court
also rejected some of the studies as too attenuated from the
appellants’ case. But its rejection of these studies is not tan-
tamount to a requirement of absolute precision. Instead, its
rejection is a recognition of an analytical gap too wide to be
bridged.
   Take, for example, the rejected study that analyzed the
carcinogenic effect of vinyl chloride on lab rats.7 Cesare Mal-
toni, et al., Carcinogenity Bioassays of Vinyl Chloride Monomer:
A Model of Risk Assessment on an Experimental Basis, 41 Envtl.
Health Persp. 3 (1981). This study found no statistically sig-


7For the sake of economy, we pull two studies as a representative sam-
ple of the whole—one that deals with animals and one that deals with
humans.
No. 14-3448                                                   15

nificant increase in the number of tumors developed by rats
that were fed 0.03 milligrams of vinyl chloride per kilogram
of bodyweight, (0.03 mg/kg), of vinyl chloride per day (4 to 5
days per week, for 59 weeks), over the control group of rats
that were fed only olive oil. Id. at 16, 21. Remarkably, 0.03
mg/kg is ten times higher than the amount the appellants
allegedly ingested—Dr. Ryer-Powder estimates they ingest-
ed 0.003 mg/kg. And the rats ingested it over a period of
time much longer, at least in rat years, than the children’s
exposure here. Given these facts, Dr. Ryer-Powder’s conclu-
sion that this study shows that C.W. and E.W. are now at an
increased risk of developing cancer was an inferential leap
that the district court was rightly unwilling to make.
    This second rejected study, which analyzed the effect of
vinyl chloride on French workers, fares no better. See Steven
J. Smith, et al., Molecular Epidemiology of p53 Protein Mutations
in Workers Exposed to Vinyl Chloride, 147 Am. J. Epidemiology
302 (1998). It drew from a group of adults over the course of
five years. Id. at 302. Yet C.W. and E.W. were exposed to vi-
nyl chloride for less than seventeen and seven months, re-
spectively. As for the levels of exposure, the workers were
divided into exposure groups with the average level set at
3,735 parts per million. Id. at 304. That amount is over 1,000
times greater than the 3 parts per billion to which the chil-
dren were exposed. Nevertheless, Dr. Byers offered it in
support of her opinion that the children are at an increased
risk of developing cancer.
    In rejecting these studies and others like it, the district
court properly exercised its role as gatekeeper under Daub-
ert. And the district court acknowledged that studies need
not be precisely analogous to meet the Daubert reliability
16                                                    No. 14-3448

standard. Textron I, supra, at *53 (“I am mindful that an ex-
pert’s opinion does not have to be unequivocally supported
by epidemiological studies in order to be admissible under
Daubert.”) (internal quotations and citations omitted). Ac-
cordingly, it is entitled to deferential review in the second
stage of our analysis.
     C. The District Court’s Exclusion of the Experts’ Testimony
    Under the second step in our analysis, we apply the
abuse of discretion standard of review. Brumley, 217 F.3d at
911. This standard demands that we “not disturb the district
court’s findings unless they are manifestly erroneous.” Laps-
ley v. Xtek, Inc., 689 F.3d 802, 809 (7th Cir. 2012) (citations
omitted). A deferential standard, it flows from the “wide lati-
tude and discretion” that district courts enjoy when deciding
whether to admit or exclude expert testimony. Ervin, 492
F.3d at 904 (quoting Wintz by & Through Wintz v. Northrop
Corp., 110 F.3d 508, 512 (7th Cir. 1997)).
    Here, the district court did not abuse its discretion in ex-
cluding the appellants’ experts. The district court’s primary
concern, and ours on appeal, is the failure of the experts to
connect the dots from the studies to the illnesses endured by
the children. This is the Joiner problem to which we referred
earlier. When a district court “conclude[s] that there is simp-
ly too great an analytical gap between the data and opinion
proffered” such that the opinion amounts to nothing more
than the ipse dixit of the expert, it is not an abuse of discre-
tion under Daubert to exclude that testimony. Joiner, 522 U.S.
at 146. That is what happened here.
   The appellants counter with a reasonable argument. They
note that there are no studies available on the impact of vi-
No. 14-3448                                                   17

nyl chloride on children. These studies are unavailable be-
cause of the ethical and moral concerns of introducing toxins
to children. This point is well taken and, we note, the district
court recognized as much. Textron I, supra, at *44 (“[I]t’s
wholly unsurprising that Dahlgren was unable to cite a
study at the precise dose and duration that the … children
were subject to, and nothing in the case law says that he
must do so.”).
    But there is a scientific end-around to make up for this
dearth in literature. Scientists have developed computer-
based models to extrapolate from animal data to human sub-
jects, and from high doses to lower doses. Bernard D.
Goldtsein & Mary Sue Henifin, Reference Guide on Toxicology
in Federal Manual on Scientific Evidence 646 (3d ed. 2011)
(“The mathematical depiction of the process by which an ex-
ternal dose moves through various compartments in the
body until it reaches the target organ is often called physio-
logically based pharmokinetics or toxicokinetics.”). Gold-
stein and Henifin recognize that “[a]dvances in computa-
tional toxicology” have facilitated this approach. Id. at 646–
47. The EPA recognizes this and other methods of extrapola-
tion as valid approaches to bridging the gap between the
studies and the general public. U.S. Envtl. Prot. Agency, Toxi-
cological Review of Vinyl Chloride 37–63 (2000) (discussing
methods to extrapolate to low doses and to humans, general-
ly). The appellants’ experts do not mention or refer to this
model of extrapolation.
    As for the district court’s rejection of the attenuated stud-
ies themselves, that too falls within the ambit of Joiner. See
522 U.S. at 144–45 (“The studies were so dissimilar to the
facts presented in this litigation that it was not an abuse of
18                                                  No. 14-3448

discretion for the District Court to have rejected the experts’
reliance on them.”). The district court’s decision fell within
its wide scope of discretion, and we will not upset it here.
    The district court also found fault in the experts’ differen-
tial etiology because, in its view, the etiology was not relia-
ble. We agree. Dr. Dahlgren’s differential etiology does not
present the reliability that Daubert demands. An example is
helpful here. After ruling in the alternative causes of “inher-
itance, allergy, infection or another poison,” Dr. Dahlgren
then ruled them out because, in his view, these causes
“would have been detected by [the appellants’] doctors and
treated accordingly.”
    This approach is not the stuff of science. It is based on
faith in his fellow physicians—nothing more. The district
court did not abuse its discretion in rejecting it. As for Dr.
Byers’s differential etiology, it showcases a rigor missing in
Dr. Dahlgren’s. But it nevertheless contains a fatal flaw: rul-
ing in vinyl chloride as a cause in the first place. Without the
benefit of analogous studies and an acceptable method of
extrapolation, Dr. Byers, like the other experts, is forced to
take a leap of faith in pointing to vinyl chloride as having the
capacity to cause the injuries (and risk of injury) to C.W. and
E.W. The district court ably performed its gatekeeper role in
shielding a jury from this leap.
    Dr. Ryer-Powder seeks a boost from government regula-
tion. Recall her report: “One means by which the health risks
from exposure to chemicals can be assessed is by compari-
son to government standards and regulation.” But exceed-
ance of government regulation, as we’ve held before, does
not by itself prove causation. See Cunningham, 569 F.3d at 675
(rejecting this approach because the expert would have to
No. 14-3448                                                            19

know “the specific dangers” that caused the regulatory
agency “to pick the safe level it did”). The district court did
not abuse its discretion in rejecting this methodology. To the
extent the experts also based their opinions on the timing of
C.W.’s and E.W.’s injuries, the district court properly rejected
this methodology as well. Ervin, 492 F.3d at 904–05 (7th Cir.
2007) (“The mere existence of a temporal relationship be-
tween taking a medication and the onset of symptoms does
not show a sufficient causal relationship.”).
   In sum, the district court did not abuse its discretion in
excluding the appellants’ experts. We now turn to the final
question on appeal: whether that exclusion was fatal to the
appellants’ toxic-tort case.
    D. Summary Judgment
    We review a district court’s grant of summary judgment
de novo. Hanover Ins. Co. v. N. Bldg. Co., 751 F.3d 788, 791 (7th
Cir. 2014). Summary judgment is appropriate where the ad-
missible evidence reveals no genuine issue of any material
fact. Fed. R. Civ. P. 56(c).
    Given the complex nature of this case, and considering
the appellants make no argument that their case can survive
without the excluded experts,8 this final issue can be re-
solved more simply. With no experts to prove causation—be
it general or specific, see Bowens, 857 N.E.2d at 389—the ap-


8 Before the district court, the appellants’ argued that the opinions of
their treating physicians, Doctors Claude Ruffalo and Jerrod Feldman,
along with Textron’s expert, Dr. Thomas McHugh, were sufficient to es-
tablish causation to survive summary judgment. Textron II, supra, at *5–6.
These arguments are not advanced here.
20                                                            No. 14-3448

pellants cannot prove their toxic-tort case under Indiana law.
Accordingly, we hold that summary judgment in this case
was proper.
    Before concluding, however, we must part ways with the
district court’s rationale in granting summary judgment. For
we think the court unnecessarily foreclosed an issue better
left open for future litigants in other cases. The district court
held that differential etiology “cannot be used to support
general causation.” C.W. v. Textron, 2014 U.S. Dist. LEXIS
141593, at *11 (N.D. Ind. Oct. 3, 2014) (“Textron II”). It reiter-
ated this holding in a footnote: “Differential [etiology] is
admissible only insofar as it supports specific causation,
which is secondary to general causation … .” Id. at *12 n.3.
    We disagree with the district court’s categorical exclusion
of differential etiology as a method to establish general cau-
sation. Indiana recognizes the important role that differential
etiology plays in toxic-tort cases. Hannan v. Pest Control
Servs., 734 N.E.2d 674, 682 (Ind. Ct. App. 2000). And there
may be a case where a rigorous differential etiology is suffi-
cient to help prove, if not prove altogether, both general and
specific causation.9 The Second Circuit already takes this ap-


9 The Federal Rules of Evidence contemplate using one piece of evidence
to help prove multiple facts in issue. That is why, in appropriate circum-
stances, Rule 105 allows a district court to restrict the scope of evidence
and instruct a jury accordingly. Fed. R. Evid. 105. For this reason, among
others, at least one scholar believes differential etiology “should be ad-
missible on general causation.” Edward J. Imwinkelreid, The Admissibility
and Legal Sufficiency of Testimony About Differential Diagnosis (Etiology): Of
Under–and Over–Estimations, 56 Baylor L. Rev. 391, 406 (2004) (“[A]n etio-
logical opinion expressly addressing specific causation is also relevant to
general causation; a plausible finding that a factor was the cause in a
                                                               (continued…)
No. 14-3448                                                              21

proach. See Ruggiero v. Warner-Lambert Co., 424 F.3d 249, 254
(2d Cir. 2005) (“There may be instances where, because of
the rigor of differential diagnosis performed, the expert’s
training and experience, the type of illness or injury at issue,
or some other … circumstance, a differential diagnosis is suf-
ficient to support an expert’s opinion in support of both gen-
eral and specific causation.”). And we adopt it today.
                           III. CONCLUSION
    For the foregoing reasons, the district court properly ap-
plied the Daubert framework to the appellants’ experts. It did
not abuse its discretion in excluding their testimony. With-
out expert testimony to prove general and specific causation,
the appellants could not prove their case. Although we disa-
gree with the district court that differential etiology can nev-
er be used to establish general causation, we nevertheless
AFFIRM its final judgment.




(…continued)
specific case slightly strengthens the inference that the factor in question
is capable of causing illness which the plaintiff developed.”).
