                This opinion is subject to revision before final
                       publication in the Pacific Reporter
                                2020 UT 21


                                   IN THE

      SUPREME COURT OF THE STATE OF UTAH

              RICHARD TAYLOR and DEANNE TAYLOR,
                          Petitioners,
                                      v.
  UNIVERSITY OF UTAH, UNIVERSITY HOSPITAL, and UNIVERSITY OF
     UTAH PHYSICAL MEDICINE AND REHABILITATION CLINIC,
                         Respondents.


                           No. 20190127
                       Heard January 13, 2020
                         Filed May 8, 2020

           On Certiorari to the Utah Court of Appeals


                     Third District, Salt Lake
                  The Honorable Robert P. Faust
                         No. 140903769

                                Attorneys:
  James W. McConkie, Bradley H. Parker, W. Alexander Evans,
               Salt Lake City, for petitioners
 Curtis J. Drake, Parker A. Allred, Salt Lake City, for respondents


  JUSTICE HIMONAS authored the opinion of the Court, in which
      CHIEF JUSTICE DURRANT, ASSOCIATE CHIEF JUSTICE LEE,
          JUSTICE PEARCE, and JUSTICE PETERSEN joined.

   JUSTICE HIMONAS, opinion of the Court:
                          INTRODUCTION
    ¶1 Utah Rule of Evidence 702 requires district courts to
exclude expert testimony that fails to satisfy any one of several
threshold requirements. These requirements include ―a threshold
showing that the principles or methods that are underlying in the
testimony . . . are based upon sufficient facts or data.‖ UTAH R.
EVID. 702(b)(2). We are asked whether such a threshold showing is
                  TAYLOR v. UNIVERSITY OF UTAH
                       Opinion of the Court

present where a method of logical deduction is based upon broad
and attenuated facts. We hold that it is not.
                         BACKGROUND1
   ¶2 Richard and Deanne Taylor‘s daughter, Ashley, was
diagnosed at a young age with a neurological disorder that
caused her to suffer from spasticity. To control this effect, Ashley
received baclofen2 through a catheter and an implanted baclofen
pump that delivered it into the thecal sac around her spinal cord.
    ¶3 On April 17, 2013, Ashley woke up suffering from severe
shaking in her legs. She saw a physician at the University of Utah
Hospital, where she received an oral dose of baclofen. The
physician performed several tests, gave Ashley more oral
baclofen, and instructed her to return the next day. Although the
following day‘s tests did not show an obvious sign of a problem,
the physician thought there might still be a problem with the
pump. During that period of time, Ashley kept vomiting and had
difficulty keeping down oral doses of baclofen. After further
consultation, the physician recommended surgery to replace the
pump and the catheter connected to it. The surgery was
performed the following day, April 19, 2013. Ashley‘s sister later
agreed with the statement that Ashley was ―back to herself‖ a day
after the surgery.
   ¶4 Two to three weeks later, however, Ashley began
exhibiting unusual behavioral symptoms. The Taylors consulted
Dr. Judith Gooch, who had been Ashley‘s treating physician in the
past. Dr. Gooch initially concluded that Ashley suffered from
__________________________________________________________
    1 The issue before us is not affected materially by the case facts

or by disputes the parties have about them. We provide the facts
only to give the reader the context of our opinion. And their
recitation here should not be viewed as an endorsement of either
party‘s version.
   2  The University of Utah, University Hospital, University of
Utah Physical Medicine and Rehabilitation Clinic, and the agents,
employees, and staff employed with those institutions
(collectively, the Hospital) defined baclofen in its motion at the
district court as a ―muscle relaxer that helps to control spasticity
(clonus) in the legs.‖ The Taylors have not challenged this
definition.


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baclofen overdose and completely stopped the administration of
baclofen to Ashley. Later, Dr. Gooch concluded that Ashley‘s
change in behavior was due to baclofen withdrawal—not an
overdose as she had initially found. She further concluded that
although Ashley had returned to a stable condition, she suffered,
and still suffers, from permanent cognitive injuries.
   ¶5 The Taylors brought suit against the Hospital on Ashley‘s
behalf. They alleged that the Hospital‘s treatment of Ashley‘s
baclofen withdrawal between April 17 and April 19, 2013, caused
her permanent injuries.
    ¶6 The Taylors retained Dr. Gooch as a causation expert. The
district court summarized Dr. Gooch‘s proximate cause theory as
follows: ―Baclofen withdrawal caused a metabolic disturbance,
which caused encephalopathy, which produced months-long
hallucinations and other abnormal behavior, resulting in or
causing permanent memory and cognitive function damage to
[Ashley].‖
    ¶7 After deposing Dr. Gooch, the Hospital filed a motion in
limine to exclude her testimony. The Hospital argued that the
testimony ―should be barred under Rule 702 of the Utah Rules of
Evidence because Dr. Gooch‘s opinion is not based upon
sufficient facts or data.‖ In its motion, the Hospital relied on Dr.
Gooch‘s concession in her deposition that ―there is not a single
reported case of baclofen withdrawal in which the patient
remained stable throughout the episode and went on to suffer
permanent neurological injury.‖ Dr. Gooch also conceded that she
had ―never seen a patient experience the injuries that [Ashley]
claims to have suffered.‖
    ¶8 The Taylors opposed the motion. With their
memorandum, they attached a declaration from Dr. Gooch where
she again conceded the facts mentioned by the Hospital but
contended they were irrelevant. Dr. Gooch declared that her
personal experience allowed her to logically deduce that baclofen
withdrawal can cause encephalopathy with permanent injuries,
although she had not witnessed such an occurrence, and could
not point to it in the medical literature. Dr. Gooch further
explained that she had performed a differential diagnosis to
determine proximate cause.
   ¶9 The district court agreed with the Hospital and excluded
Dr. Gooch‘s testimony. It concluded that ―Dr. Gooch [did] not

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have facts and data sufficient upon which to base her opinions or
to employ her method for evaluating the causal connection in this
case,‖ that ―she present[ed] no medical information or reports
supporting her position,‖ and that ―her personal experience‖
likewise failed to provide a basis for her testimony.
    ¶10 The Taylors appealed. In their appeal, they outlined a
similar argument to the one they had made at the district court.
The court of appeals was unpersuaded and affirmed. Taylor v.
Univ. of Utah, 2019 UT App 14, ¶ 1, 438 P.3d 975. The court of
appeals explained that although logical deduction was not per se
an ―unreliable method,‖ in this case, Dr. Gooch lacked ―sufficient
facts and data to employ such a method.‖ Id. ¶ 10 n.1; see also id.
¶ 16.
  ¶11 The Taylors petitioned for certiorari, which we granted.
We exercise jurisdiction under Utah Code section 78A-3-102(3)(a).
                    STANDARD OF REVIEW
   ¶12 On certiorari, ―we review the decision of the court of
appeals and not that of the district court.‖ State v. Hansen, 2002 UT
125, ¶ 25, 63 P.3d 650 (citation omitted) (internal quotation marks
omitted). And ―we review the decision of the court of appeals for
correctness.‖ Id. (citation omitted) (internal quotation marks
omitted).
    ¶13 But ―[t]he correctness of the court of appeals‘ decision
turns, in part, on whether it accurately reviewed the [district]
court‘s decision under the appropriate standard of review.‖ State
v. Apodaca, 2019 UT 54, ¶ 25, 448 P.3d 1255 (citation omitted). In
this case, the issue is the admission of evidence. ―With regard to
the admission of evidence, most decisions involve a threshold
statement of the legal principle governing admission or exclusion,
findings of facts pertinent to a determination, and the application
of the legal principle to the facts at hand with regard to
admissibility.‖ Arnold v. Grigsby, 2018 UT 14, ¶ 9, 417 P.3d 606.
―We review the legal questions to make the determination of
admissibility for correctness.‖ State v. Workman, 2005 UT 66, ¶ 10,
122 P.3d 639 (citation omitted). ―We review the questions of fact
for clear error.‖ Id. (citation omitted). And finally, ―we review the
district court‘s ruling on admissibility for abuse of discretion.‖ Id.
(citation omitted).




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                            ANALYSIS
   ¶14 We granted certiorari on the question of whether the
court of appeals erred in affirming the district court‘s exclusion of
Dr. Gooch‘s expert testimony. We find no error and,
consequently, we affirm.
    ¶15 We hold that given the gaps between the facts Dr. Gooch
relied on and her logical deduction, it was not an abuse of
discretion for the district court to exclude her testimony. Further,
we address two arguments the Taylors make. First, we reject their
argument about our case law regarding Utah Rule of Evidence
702 and clarify that the district court and court of appeals
properly applied it. Second, we refuse to consider a new
argument the Taylors raise in their reply brief, offering differential
diagnosis testimony from Dr. Gooch, because it was untimely
made.
  I. BECAUSE DR. GOOCH‘S METHOD WAS NOT BASED ON
  SUFFICIENT FACTS OR DATA, THE DISTRICT COURT DID
       NOT ABUSE ITS DISCRETION IN EXCLUDING IT
    ¶16 Utah Rule of Evidence 702 ―assigns to trial judges a
‗gatekeeper‘ responsibility to screen out unreliable expert
testimony.‖ UTAH R. EVID. 702 advisory committee notes; see also
State v. Lopez, 2018 UT 5, ¶ 20, 417 P.3d 116; Eskelson v. Davis Hosp.
& Med. Ctr., 2010 UT 59, ¶ 12, 242 P.3d 762. The applicable
standard of review for a decision about admissibility, abuse of
discretion, reflects the respect we have for a district court‘s
determination in these preliminary issues. See State v. Jones, 2015
UT 19, ¶ 12, 345 P.3d 1195; State v. Workman, 2005 UT 66, ¶ 10, 122
P.3d 639.
    ¶17 The rule provides trial judges the framework to fulfill this
assignment. Relevant to this case are subsections (b) and (c).
Subsection (b) requires the party seeking admission of the expert
testimony to make a ―threshold showing that the principles or
methods that are underlying in the testimony‖ are ―reliable,‖
―based upon sufficient facts or data,‖ and ―have been reliably
applied to the facts.‖ UTAH R. EVID. 702(b). Subsection (c) allows
satisfaction of subsection (b)‘s ―threshold showing‖ if the
―underlying principles or methods, including the sufficiency of
facts or data and the manner of their application to the facts of the
case, are generally accepted by the relevant expert community.‖
Id. 702(c).

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                  TAYLOR v. UNIVERSITY OF UTAH
                       Opinion of the Court

    ¶18 The parties dispute whether the principles or methods
underlying Dr. Gooch‘s expert testimony are based on sufficient
facts or data, and whether these facts or data are generally
accepted by the relevant expert community as a sufficient basis
for the principles or methods underlying her testimony. They are
not. The analytical gaps between the facts used as ―principles‖ in
Dr. Gooch‘s opinion and her proximate cause logical deduction
from them are too great to be sustained. In other words, the
method Dr. Gooch used—logical deduction—is not based on
sufficient facts or data. Given these gaps, it cannot be said, and
there is no showing, that the relevant expert community generally
accepts the sufficiency of such facts as a basis for logical
deduction. Under these circumstances, the district court did not
abuse its discretion when it excluded the testimony.
    ¶19 We start by analyzing Utah Rule of Evidence 702(b).3 The
Taylors argue that Dr. Gooch‘s testimony is a logical deduction
based on three undisputed facts she has personally experienced as
a treating physician. The three facts are that (1) baclofen
withdrawal can cause a metabolic disturbance, (2) metabolic
disturbance can cause encephalopathy, and (3) encephalopathy
can result in permanent rather than merely temporary deficits.
Based on these facts, Dr. Gooch deduced that she knows ―through
[her] personal experience . . . that baclofen withdrawal can cause
encephalopathy and that the symptoms associated with the
encephalopathy can be permanent.‖ Dr. Gooch also stated that the
literature is ―consistent with [her] personal experience.‖
   ¶20 This court has previously acknowledged that ―even
highly technical or scientific testimony may be based on simple
inductive or deductive reasoning that the average person uses
every day.‖ State v. Rothlisberger, 2006 UT 49, ¶ 34, 147 P.3d 1176.
But merely invoking a logical deduction method does not make
expert testimony admissible. The logical deduction must still be
__________________________________________________________
   3 The Taylors also make arguments about subsection (c), as

they did in the court of appeals. Neither the district court nor the
court of appeals based their decision to exclude the evidence on
subsection (c), so its analysis is not relevant here. However, as we
explain below, the facts or data Dr. Gooch used are not generally
acceptable in the relevant expert community as a basis for logical
deduction.


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based on sufficient facts or data, as rule 702(b)(2) orders. Here it is
not.
    ¶21 The Taylors‘ counsel explained at the district court
hearing that logical deduction is appropriate only so long as ―each
step is a reliable step that takes you logically from one point to the
next.‖ But logical deduction is not appropriate where ―[t]he
analytical gap between the evidence presented and the inferences
to be drawn . . . is too wide.‖ Turpin v. Merrell Dow Pharms., Inc.,
959 F.2d 1349, 1360–61 (6th Cir. 1992). Indeed, ―[a] court may
conclude that there is simply too great an analytical gap between
the data and the opinion proffered, i.e., whether the expert has
unjustifiably extrapolated from an accepted premise [or data] to
an unfounded conclusion.‖ Nelson v. Enid Med. Assocs., Inc., 376
P.3d 212, 222 (Okla. 2016) (alterations in original) (internal
quotation marks omitted) (quoting Hollander v. Sandoz Pharms.
Corp., 289 F.3d 1193, 1205 (10th Cir. 2002)).
   ¶22 Dr. Gooch derives her logical deduction from three
extremely broad facts. See supra ¶ 19. It is undisputed that two of
the terms she uses in these facts, ―metabolic disturbance‖ and
―encephalopathy,‖ can encompass numerous situations.
    ¶23 The Hospital explained (and the Taylors have not refuted)
that a ―metabolic disturbance is a type of brain dysfunction that is
usually caused by toxic exposure (drugs, alcohol, toxic chemicals)
or by a deficiency in a hormone or vitamin (e.g., B12) in the
body.‖ The Taylors‘ counsel referred to metabolic disturbances at
the district court hearing as situations where ―your [body is] kind
of freaking out.‖ Dr. Gooch said in her deposition that
encephalopathy ―is a term used to describe a problem in the
brain.‖ She added that it ―[t]ypically‖ appears ―in a relatively
acute onset of a structural or functional problem in the brain‖
resulting from ―a multitude of causes,‖ such as ―toxic metabolic‖
or ―other things.‖
   ¶24 Dr. Gooch explained that from her three facts she
deduced a specific plausibility. However, this deduction suffers
from the fallacy of equivocation. The fallacy of equivocation is an
argument that ―exploits the ambiguity of a term or phrase which
has occurred at least twice in an argument, such that on the first
occurrence it has one meaning and on the second another
meaning.‖ Fallacies, STANFORD ENCYCLOPEDIA OF PHILOSOPHY,
https://plato.stanford.edu/entries/fallacies/#CorFal (last visited
May 1, 2020).
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                  TAYLOR v. UNIVERSITY OF UTAH
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    ¶25 The gap this ambiguity creates often stems from
contextual differences. See, e.g., United States v. Brawner, 471 F.2d
969, 988 (D.C. Cir. 1972) (en banc)4 (―There may be a tug of appeal
in the suggestion that law is a means to justice and the jury is an
appropriate tribunal to ascertain justice. This is a simplistic
syllogism that harbors the logical fallacy of equivocation, and fails
to take account of the different facets and dimensions of the
concept of justice.‖); In re Ohio Execution Protocol Litig., No. 2:11-
CV-1016, 2018 WL 2118817 *20 (S.D. Ohio May 8, 2018) (―The
paper begins with Judge Frost‘s description of the use of the two-
drug protocol in the McGuire execution as an ‗experiment.‘ . . . [I]t
is the fallacy of equivocation to take that word from Judge Frost‘s
decision and apply it in other contexts where the word
‗experiment‘ is used.‖ (citation omitted)); United Servs. Auto. Ass’n.
v. Baggett, 209 Cal. App. 3d 1387, 1396 (1989) (rejecting an
argument that the word ―accident‖ was ambiguous as used in a
specific insurance policy simply because ―accident‖ has many
meanings in the abstract, and explaining that the court ―would
commit the fallacy of equivocation to conclude such abstract
ambiguity renders the word ambiguous as used in insurer‘s
policy‖).
   ¶26 Here, the attenuation is in the terms‘ broad meanings.
Dr. Gooch committed the fallacy of equivocation by failing to
account for whether the types of ―metabolic disturbances‖ that
can be caused by baclofen withdrawal are the same types of
metabolic disturbances that can cause encephalopathy. Similarly,
she has not supported the analytical leap to the conclusion that
the types of encephalopathy caused by metabolic disturbances


__________________________________________________________
    4 Legal search engines suggest that Brawner was superseded by

statute, alleging that the United States Supreme Court stated so in
Shannon v. United States, 512 U.S. 573, 575 (1994). After reading the
Shannon opinion, and reviewing cases that cited to Brawner after
Shannon, we disagree with this suggestion. Shannon refers to
Brawner only when explaining the District of Columbia law
regarding successful insanity defense. But even if Shannon
somehow implicitly stated that Brawner was superseded by
statute, this has no significance for our use of the opinion, as a
mere example of a fallacy of equivocation.


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(whether caused by baclofen withdrawal or not) can cause
permanent injuries, as the Taylors argue happened here.5
    ¶27 Additionally, in her syllogism, Dr. Gooch makes an
implicit sub-conclusion that ignores the impact of baclofen
restoration on metabolic disturbances and encephalopathy. 6 For
example, her deduction skips over a plausible difference between
metabolic disturbances whose effects are typically alleviated
when baclofen is restored, and metabolic disturbances whose
effects are not thus alleviated. The same is true for her use of the
term encephalopathy.
__________________________________________________________
    5 Both the district court and the court of appeals focused on the

fact that Dr. Gooch could not show, from personal experience or
the literature, any case of encephalopathy, caused by baclofen
withdrawal that resulted in permanent injury where baclofen was
restored within forty-eight hours. Dr. Gooch argued that several
cases of baclofen withdrawal had resulted in death, which is a
permanent injury, and therefore other permanent injuries are
plausible. That argument is perhaps an even more apropos
example of the fallacy of equivocation than the examples cited
above. Further, the cases Dr. Gooch relied on are all significantly
distinguishable. Most importantly, all involved situations where
baclofen was not restored prior to death. Ashley‘s baclofen was
restored.
    Additionally, the Taylors argued in their reply brief that
Ashley‘s condition during the baclofen withdrawal was not stable,
and the cases that had resulted in death also had non-stable
baclofen withdrawals, and therefore are applicable to her case.
Although Dr. Gooch raised this point in her declaration, it was not
presented in this court until the Taylors reply brief. We therefore
decline to address it. See infra ¶ 50.
   6 At the district court hearing, the Taylors‘ counsel argued that
once metabolic disturbances and encephalopathies occur, they
―work[] according to [their] own rules,‖ and therefore their effects
should be evaluated without considering their origin. The Taylors
did not repeat this argument to this court, and Dr. Gooch
contradicted this argument in her deposition. She stated that ―the
ultimate outcome depends on how quickly intrathecal Baclofen
withdrawal is managed,‖ connoting a connection between the
baclofen withdrawal and the resulting encephalopathy effects.


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   ¶28 Because courts ―require inferences to be sound logically,
and refuse to allow a jury of laymen to engage in guesswork,
speculation and conjecture,‖ Hamilton v. Kirson, 96 A.3d 714, 730
(Md. 2014) (citation omitted) (internal quotation marks omitted),
we hold that the facts Dr. Gooch relied on are insufficient to
support her method of logical deduction.
    ¶29 Analyzing these facts under Utah Rule of Evidence 702(c)
leads to the same conclusion.7 Because of the gaps outlined above,
it cannot be said that the three facts Dr. Gooch used are generally
accepted by the relevant expert community as sufficient to
employ a legal deduction method that yields her proximate cause
testimony.
    ¶30 It is common for experts to extrapolate from data.
However, the analytical gaps between the broad facts and the
case-specific conclusion mean that Dr. Gooch asks the trier of fact
to rely on her ipse dixit.8 There is nothing in rule 702 that requires
a court to allow that. And so, the district court did not abuse its
discretion by excluding the testimony. See Gen. Elec., Co. v. Joiner,
522 U.S. 136, 146 (1997) (―[N]othing in either Daubert or the
Federal Rules of Evidence requires a district court to admit
opinion evidence that is connected to existing data only by the ipse
dixit of the expert. A court may conclude that there is simply too
great an analytical gap between the data and the opinion
proffered.‖).
    ¶31 In her declaration, Dr. Gooch stated her logical deduction
is consistent with the literature. But it is only not inconsistent. In
fact, Dr. Gooch explained in the same declaration that the
literature ―does not indicate that baclofen withdrawal cannot
cause permanent injury,‖ but the literature includes only the
permanent injuries of death and multi-organ failure. She
presented no literature referring to the kind of permanent injury

__________________________________________________________
   7 In Lopez, we held the inverse, which is consistent with our

holding here. 2018 UT 5, ¶ 29. We found that the expert testimony
there did not comply with the rule 702(c) requirement and
explained that for the same reasons it did not comply with rule
702(b). Id.
   8―Something asserted but not proved.‖ Ipse Dixit, BLACK‘S
LAW DICTIONARY (11th ed. 2019).


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Ashley suffered. As the Hospital succinctly put it in its motion in
limine, if ―[Dr. Gooch] were to attempt to publish her opinion
regarding [Ashley] in a peer-reviewed journal, the first question
likely to be asked is, ‗Where is your data?‘ Because there are no
supporting facts or data, the article would never be published.‖
   ¶32 In sum, the facts and data underlying the logical
deduction method Dr. Gooch used are insufficient to withstand a
rule 702 inquiry.
       II. THE TAYLORS‘ ARGUMENTS FOR REVERSAL
                   ARE UNPERSUASIVE
    ¶33 The Taylors resist this outcome with two arguments. First,
they claim that the district court and court of appeals
misconstrued our case law and impermissibly assessed the
sufficiency of the facts or data underlying Dr. Gooch‘s testimony
instead of those underlying her method. Second, in their reply
brief, the Taylors offer an additional argument on proximate
causation—a specific causation argument based on differential
diagnosis.
   ¶34 The first argument miscomprehends what the district
court and the court of appeals decided. The Taylors forfeited the
second argument because they raised it only in their reply brief.
Although we cannot properly adjudicate the argument because
the Taylors raised it too late, we point out two issues that arise
from the Taylors‘ briefing, which lead us to believe it would be
bound to fail even if considered.
         A. The District Court and Court of Appeals Did Not
          Mistakenly Analyze the Testimony Instead of the
                Principles or Methods Underlying It
    ¶35 The Taylors argue that the district court and the court of
appeals construed Dr. Gooch‘s testimony as experience based.
Consequently, they allege, the district court and court of appeals
reviewed whether her testimony itself, i.e., her conclusion, is
based on sufficient facts or data, allegedly under the standard we
set out in Eskelson v. Davis Hospital & Medical Center, 2010 UT 59,
¶ 12, 242 P.3d 762.
   ¶36 According to the Taylors, this was a mistake because
while the facts Dr. Gooch relied on as the basis for her logical
deduction derived from her experience, her testimony was based
on a ―method[]‖—logical deduction. When a testimony is based

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on ―principles or methods,‖ the Taylors advance, a court‘s rule
702 review is limited to the facts or data underlying those
principles or methods and cannot reach the actual testimony,
under State v. Clopten, 2015 UT 82, ¶ 51, 362 P.3d 1216.
    ¶37 This alleged difference matters because the Taylors argue
that the district court and court of appeals excluded Dr. Gooch‘s
testimony on the ground that they did not find facts or data
supporting her conclusion. The Taylors insist this was
impermissible and that the relevant question is whether the
method Dr. Gooch used—logical deduction—is based on sufficient
facts or data.
   ¶38 We agree with the Taylors that the relevant question is
whether Dr. Gooch‘s method was based on sufficient facts or data.
But this does not help them because, as we explain above,
Dr. Gooch‘s method was not based on sufficient facts or data.
    ¶39 Regardless, the Taylors‘ argument as to our case law and
its application by the district court and court of appeals is
meritless. First, the Taylors wrongly construe our decisions in
Eskelson and Clopten. Both decisions apply rule 702 in the same
manner. Second, the district court and court of appeals properly
analyzed this case under our rule 702 precedent. Specifically, both
courts analyzed the facts or data that formed the basis of Dr.
Gooch‘s method, not her testimony.
    ¶40 First, rule 702(b)‘s ―reliability requirement does not apply
to expert witnesses‘ conclusions, but rather to the ‗principles and
methods‘ underlying their conclusions.‖ Clopten, 2015 UT 82, ¶ 51.
Contrary to the Taylors‘ argument, Eskelson did not hold
otherwise. Eskelson was this court‘s first opportunity to address
rule 702 after its amendment in 2007. We elaborated on the
amendment and explained the relationship between the amended
rule and our past case law. Eskelson, 2010 UT 59, ¶¶ 9–12. We
established no special rule regarding experience-based expert
testimony. We merely applied the rule to the facts of that case.
    ¶41 The expert testimony in dispute in Eskelson lacked an
identified method. Instead, the expert relied on ―his experience as
a physician, in dealing with similar situations‖ to the one in
question. Id. ¶ 15. The district court there held the testimony
should not be admitted because the lack of an identified method
meant that the expert testimony was not reliable. Id. ¶ 13. We
rejected that argument and held that ―[i]n [that] case, amended

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rule 702 requires no more‖ than the expert‘s experience because
the ―[i]dentification of a methodology is not necessary where
exposure to a nearly identical situation forms the basis of the
expert‘s opinion.‖ Id. ¶ 15. We also stressed that ―[w]hat is
required for a threshold showing of reliability will vary
depending on the complexity of the particular case.‖ Id.
   ¶42 In other words, this court held in Eskelson that when an
expert can present exposure to a nearly identical situation, this
exposure acts as their method de facto. This court cabined its
holding by adding the case‘s complexity as a factor in that
determination. See id.
   ¶43 The situation that the Eskelson expert testimony addressed
was not complex at all, but rather routine for him—the removal of
foreign objects from children‘s ears. See id. In that type of case, the
expert‘s ―exposure to a nearly identical situation‖ sufficed to
―constitute[] a threshold showing of reliability.‖ Id. This court
then treated the expert‘s exposure as his de facto method and
examined the facts or data that formed its basis. Id. ¶ 16.
    ¶44 In Clopten, the petitioner argued that the State‘s expert
testimony was not reliable because ―his conclusions differed from
those of the majority of researchers.‖ 2015 UT 82, ¶ 50. We
rejected that argument ―because rule 702(b)‘s reliability
requirement does not apply to expert witnesses‘ conclusions, but
rather to the ‗principles and methods‘ underlying their
conclusions.‖ Id. ¶ 51. We explained that in that case, ―nothing
amiss has been identified in the methodological basis for [the
expert]‘s testimony,‖ id. ¶ 52, and therefore the testimony was
admissible under the rule. Id. ¶¶ 49–52.
    ¶45 Eskelson and Clopten do not offer different standards for
expert opinion admissibility under rule 702. Both cases applied
rule 702 to the specific facts they adjudicated. In Eskelson, the
expert‘s near-identical experience acted as his de facto method,
and the court examined the sufficiency of the facts or data
underlying it. 2010 UT 59, ¶ 16. In Clopten, this court held that
although the expert‘s conclusions were not generally accepted in
the relevant expert community, these conclusions were based on
―a thirty-year history of peer-reviewed field studies‖ and on a
―generally accepted principle of psychological science.‖ 2015 UT
82, ¶ 52. Both cases, therefore, examined the sufficiency of the
facts or data that formed the basis for the relevant expert‘s
―method.‖ The differences between them are merely factual.
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                       Opinion of the Court

   ¶46 Second, the district court and court of appeals correctly
applied our precedent to evaluate the facts or data underlying the
method Dr. Gooch used in her testimony. Because Eskelson and
Clopten represent the same standard, the use of either in a rule 702
analysis is valid.
    ¶47 The district court determined that ―Dr. Gooch [did] not
have facts and data sufficient upon which to base her opinions or
to employ her method for evaluating the causal connection in this
case as she present[ed] no medical information or reports
supporting her position nor [did] her personal experience
provide[d] such a basis.‖ The court of appeals expressly noted
that the logical deduction method Dr. Gooch applied was not
supported by ―sufficient facts or data.‖ Taylor v. Univ. of Utah,
2019 UT App 14, ¶ 16, 438 P.3d 975. The court of appeals went on
to explain that Dr. Gooch did not have ―exposure to a nearly
identical situation‖ or ―any supporting medical literature.‖ Id.
¶¶ 16–17 (citation omitted) (internal quotation marks omitted).
    ¶48 The Taylors characterize this analysis as impermissibly
scrutinizing Dr. Gooch‘s conclusions, i.e., her statement that
―baclofen withdrawal can cause encephalopathy and that the
symptoms associated with the encephalopathy can be
permanent.‖ We disagree. We recognize that some of the phrases
used by the district court and court of appeals could be construed
as assessing Dr. Gooch‘s conclusion, but ultimately, it is clear that
this is not what these courts did. As we explain above, Dr. Gooch
did not present sufficient facts or data to support her method—
logical deduction. The courts below homed in on these gaps by
discussing the lack of facts or data supporting Dr. Gooch‘s logical
inferences. These logical inferences indeed constitute her
conclusion, but they are also the heart of her method. Id. ¶ 10 n.1
(finding that the district court determined that ―the expert lacked
sufficient facts and data . . . to employ [a logical deduction]
method‖); see also id. ¶¶ 16–17.
      B. The Taylors Forfeited their Specific Causation Argument
   ¶49 In their reply brief, the Taylors presented a new argument
about proximate cause. They argued that the logical deduction
Dr. Gooch used was only general causation testimony, and that
she additionally offered specific causation testimony based on the




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                       Opinion of the Court

general causation testimony and a differential diagnosis she
performed.9
    ¶50 ―When an appellant saves an issue for the reply brief,
[they] deprive[] the appellee of the chance to respond.‖ That
leaves this court ―without a central tenet of our justice system—
adversariness. That is fatal. We have consistently held that issues
raised by an appellant in the reply brief that were not presented in
the opening brief are considered [forfeited] and will not be
considered.‖10 Kendall v. Olsen, 2017 UT 38, ¶ 13, 424 P.3d 12
(citations omitted) (internal quotation marks omitted).
    ¶51 The Taylors argue in their opening brief that Dr. Gooch‘s
logical deduction method constituted their ―proximate cause‖
testimony. The Hospital replies that ―[i]f Dr. Gooch‘s ‗logical
deduction‘ method is employed in a vacuum and not in the
context of [Ashley‘s] case, the three facts may well be sufficient
[under rule 702],‖ but ―[t]here is no evidence to support the third
fact (‗[e]ncephalopathy can result in permanent rather than
merely temporary deficits‘) in the context of this case.‖ In their
reply brief, the Taylors note that their opening argument refers
only to general causation and argue for the first time to this court
a separate argument about specific causation (or proximate
cause).
   ¶52 By only bringing this argument up in their reply brief, the
Taylors forfeited it. The fact that the Taylors made this argument
below and that the district court did not address it does not

__________________________________________________________
   9 ―General causation is whether a substance is capable of

causing a particular injury or condition in the general population,
while specific causation is whether that substance caused the
particular individual‘s injury.‖ Nelson, 376 P.3d at 221–22.
   10 Our case law uses the verb ―waive‖ in this context and not
the verb ―forfeit‖ that we use here. ―Although jurists often use the
words interchangeably, forfeiture is the failure to make the timely
assertion of a right[;] waiver is the intentional relinquishment or
abandonment of a known right.‖ Kontrick v. Ryan, 540 U.S. 443,
458 n.13 (2004) (alteration in original) (citation omitted) (internal
quotation marks omitted). We do not opine (or know) if the
Taylors relinquished their argument intentionally and therefore
prefer to use ―forfeit.‖


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                  TAYLOR v. UNIVERSITY OF UTAH
                       Opinion of the Court

change this conclusion. They did not timely raise it to this court,
and that is to their detriment.
    ¶53 Because the Taylors brought up their specific causation
argument only on reply, the Hospital could not address it, and
without the benefit of adversarial briefing, we cannot
determinatively decide it. But two issues with this argument seem
problematic to us, even without the Hospital‘s input, and lead us
to believe that it would be bound to fail even if considered.
    ¶54 First, the ―specific causation‖ argument relies on the
validity of the ―general causation‖ argument the Taylors make
and we reject above. In their reply brief, the Taylors argue that ―in
addition to the testimony regarding general causation . . .
[Dr. Gooch] provided . . . testimony regarding specific causation.‖
(Emphases omitted.) They add that it ―is based upon different
‗facts or data‘‖ (emphasis omitted) than the general causation
testimony. But the specific causation testimony does not stand on
its own two feet. It assumes that the general causation testimony
is admissible. The Taylors‘ court of appeals opening brief, to
which they refer in their reply brief in this court, explained that
―the reasonable inference upon which Dr. Gooch‘s [general
causation] conclusion is based is the principle underlying [] her
[specific causation] conclusion.‖ (Emphases omitted.)
    ¶55 Second, the differential diagnosis that the Taylors present
does not comport with evidentiary requirements. The diagnosis
here focuses only on temporal proximity. Showing causation
through differential diagnosis requires more than that. See, e.g.,
Ervin v. Johnson & Johnson, Inc., 492 F.3d 901, 904 (7th Cir. 2007)
(providing that ―expert opinions employing differential diagnosis
must be based on scientifically valid decisions as to which
potential causes should be ‗ruled in‘ and ‗ruled out‘‖); Beard v. K-
Mart Corp., 2000 UT App 285, ¶ 20, 12 P.3d 1015 (rejecting
differential-diagnosis expert testimony because ―[t]he expert
medical testimony merely established a chronological relationship
between the accident and her symptoms,‖ and ―[n]o expert
medical testimony was received that the neck and wrist surgeries
were necessitated by her accident‖).
    ¶56 In Majors v. Owens, our court of appeals found that
differential diagnosis testimony relying on patient statements,
temporal proximity, physical examination, and imaging studies
suffices under rule 702. 2015 UT App 306, ¶ 20, 365 P.3d 165. But
here the Taylors fail to present anything more than temporal
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                        Opinion of the Court

proximity. In their reply brief, the Taylors argue that Dr. Gooch‘s
differential diagnosis considered ―1) Ashley‘s health history; 2)
the extent, duration and severity of the symptoms associated with
Ashley‘s episode of baclofen withdrawal; 3) Ashley‘s condition
before and after the episode; 4) the symptoms Ashley was
experiencing after the episode; and 5) the timeline of relevant
events.‖ But when evaluating these considerations, they all relate
to the same issue—the temporal proximity between the baclofen
withdrawal episode and Ashley‘s injuries. Dr. Gooch provided no
data about other causes she ―ruled in‖ or ―ruled out.‖ See Ervin,
492 F.3d at 904. In her declaration, filed with the district court, she
also mentioned these considerations only in a conclusory manner.
And in real-time, after the baclofen withdrawal, Dr. Gooch herself
was uncertain about what was causing Ashley‘s reactions. This
also weakens the temporal proximity argument. Given the lack of
any meaningful information beyond temporal proximity, the
Taylors‘ differential diagnosis argument seems to fail on its
merits.
    ¶57 To conclude, the Taylors‘ arguments about the district
court‘s and court of appeals‘ mistakes in interpreting our case law
fail to persuade. Additionally, they forfeited their differential
diagnosis argument.
                          CONCLUSION
    ¶58 The Taylors did not make a threshold showing that the
method underlying their proximate cause expert‘s testimony—
logical deduction—was based on sufficient facts or data. Nor have
they shown that these facts or data are generally accepted by the
relevant expert community as a sufficient basis for the application
of the logical deduction method in this case. Therefore, the district
court did not abuse its discretion when it excluded the expert
testimony on proximate cause, and the court of appeals properly
affirmed.




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