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

                              2013 UT 34


                                IN THE
      SUPREME COURT OF THE STATE OF UTAH

                           WENDY HARRIS,
                            Respondent,
                                   v.
                       SHOPKO STORES, INC.,
                           Petitioner.


                            No. 20110945
                         Filed June 14, 2013

          On Certiorari from the Utah Court of Appeals

              Fourth District, American Fork Dep’t
               The Honorable Christine Johnson
                         No. 070101906

                              Attorneys:
   Michael E. Day, Nathan Whittaker, Murray, for respondent
Alain C. Balmanno, Ruth A. Shapiro, Salt Lake City, for petitioner
   Brent Gordon, Idaho Falls, John P. Lowrance, South Jordan,
                        amicus curiae

   CHIEF JUSTICE DURRANT, authored the opinion of the Court,
          in which ASSOCIATE CHIEF JUSTICE NEHRING,
   JUSTICE DURHAM, JUSTICE PARRISH, and JUSTICE LEE joined.

   CHIEF JUSTICE DURRANT, opinion of the Court:
                         INTRODUCTION
    ¶1 Wendy Harris was injured when she sat on a display
office chair at ShopKo Stores, Inc. (ShopKo), and the chair
collapsed. She sued ShopKo for negligence. At the trial, evidence
was introduced that she suffered from preexisting conditions that
may have contributed to her injury. The trial court instructed the
jury that, if it could, it should apportion damages between those
attributable to ShopKo’s negligence and those attributable to her
preexisting conditions. The jury found ShopKo negligent but
                         HARRIS v. SHOPKO
                       Opinion of the Court
awarded Ms. Harris substantially less than she requested in
damages. She appealed.
    ¶2 The court of appeals reversed the jury’s award and
remanded for a new trial. It did so on the ground that the trial
court had erred in giving the apportionment jury instruction. The
court of appeals held that, because Ms. Harris’s preexisting
conditions were asymptomatic on the date of the accident,
ShopKo was not entitled to a jury instruction permitting the jury
to allocate some portion of the damages to Ms. Harris’s
preexisting conditions. We conclude that this approach is
inconsistent with a core principle of tort law: defendants are liable
only for those injuries proximately caused by their negligence.
Under the court of appeals’ approach, where a plaintiff is
experiencing no symptoms on the date of an accident, a defendant
is liable for the full extent of the plaintiff’s injury, even though
some portion of that injury may, in fact, have been caused by a
preexisting condition. While we conclude the court of appeals
erred in this regard, however, we nevertheless affirm that court’s
grant of a new trial. We do so because at trial ShopKo did not
present evidence sufficient for the jury to apportion damages on a
nonarbitrary basis.
                         BACKGROUND
    ¶3 On March 29, 2006, Ms. Harris went to ShopKo to buy an
office chair. When she sat in one of the display chairs, the chair
fell apart. Ms. Harris fell to the floor, landing on her wrist and
tailbone. The next day, she went to the hospital after feeling “deep
abdominal pain.” She worried that “something had come loose”
from a previous surgery. The pain in Ms. Harris’s wrist eventually
went away, but the abdominal pain intensified in her lower back
and tailbone.
    ¶4 In the days after the ShopKo accident, Ms. Harris visited
her brother, Kay Whittaker, who is a family nurse-practitioner.
She later saw several doctors and therapists. These physicians
observed that she suffered severe pain in her lower back and
tailbone, which radiated down the back of her leg to her knee. Ms.
Harris underwent a variety of treatments, including pain
medication, physical therapy, massage therapy, and chiropractic
care.
    ¶5 Despite the treatment she received, Ms. Harris continued
to experience pain three years after the ShopKo accident. In 2009,
she visited Dr. Richard Rosenthal, a pain-management specialist.
Dr. Rosenthal diagnosed her with facet joint syndrome
                                 2
                        Cite as: 2013 UT 34
                       Opinion of the Court
(inflammation of one of the spinal joints) and coccydinia
(inflammation of the tailbone). Dr. Rosenthal treated Ms. Harris’s
facet joint syndrome through radio frequency lesioning—a
treatment that stops pain by severing the nerve to the facet joint.
To treat the coccydinia, Ms. Harris had to sit on a donut cushion
and receive occasional injections of steroids and anesthetics to
reduce inflammation.
    ¶6 In 2007, Ms. Harris sued ShopKo for negligence. The case
went to a jury trial in 2009. At trial, Dr. Rosenthal testified as an
expert in interventional pain medicine. He stated that facet joint
syndrome is not always trauma related and can be caused by
degenerative disc disorder due to aging. He testified that it is
more likely than not that the ShopKo accident caused Ms. Harris’s
pain and injury. He also testified that Ms. Harris received a single
treatment for possible back pain in 2002, although her chief
complaint at the time was leg pain.
    ¶7 Dr. Rosenthal further testified that Ms. Harris had been in
three automobile accidents prior to the ShopKo accident. As a
result, she had received treatment for neck and back pain,
although “there was no subsequent treatment for back pain in any
of those accidents.” Dr. Rosenthal mentioned that he saw two
references to fibromyalgia, which he described as a “chronic
condition,” in Ms. Harris’s records from 2001 but did not believe
fibromyalgia caused her pain after the ShopKo accident. He stated
that he believed Ms. Harris’s pain would eventually go away but
that she may face permanent complications from her injuries.
Finally, he testified that Ms. Harris’s medical treatment was
reasonable.
    ¶8 Following Dr. Rosenthal’s testimony, Ms. Harris called,
among others, Dr. Eric Hogenson, Mr. Kay Whittaker, and
Dr. Rodney Scuderi to testify. Each witness testified that he
treated Ms. Harris after the ShopKo accident. First, Dr. Hogenson,
Ms. Harris’s family-practice physician, testified that he treated
Ms. Harris for back pain. He testified that her back pain began
after the ShopKo incident. He also testified that Ms. Harris’s
records indicate that he treated her for fibromyalgia and
depression in 1997. Second, Mr. Whittaker, a family nurse-
practitioner, also treated Ms. Harris for back pain shortly after the
ShopKo incident. He testified that he ordered x-rays and that the
x-rays did not show any fractures. Finally, Dr. Scuderi,
Ms. Harris’s chiropractor, testified that he treated Ms. Harris
shortly after the ShopKo incident. He testified that, in his opinion,
her fall at ShopKo caused her lower-back injury. He also testified
                                 3
                         HARRIS v. SHOPKO
                       Opinion of the Court
that his treatment of her was reasonable, although it did not
provide lasting relief.
    ¶9 On cross-examination, ShopKo presented Dr. Scuderi
with records of Ms. Harris’s past medical treatment. These records
included a 1998 hospital visit for “cervical strain and to rule out a
disc herniation”; a 2001 hospital visit following a car accident for
“diffuse neck pain”; and a 2002 hospital visit for “excruciating
discomfort in the lumbar area,” which led to a diagnosis of “left
leg pain and questionable sciatica.” Dr. Scuderi then explained
that Ms. Harris’s symptoms after the ShopKo incident were not
consistent with a chronic condition. He noted that “[i]t’s not
unusual for a patient of Ms. Harris’s age to have some neck and
back pain.” On redirect, Dr. Scuderi testified that nothing in
Ms. Harris’s past medical records indicated that she had a chronic
lower-back condition prior to visiting him.
    ¶10 Dr. Alan Colledge testified for ShopKo. He practices
family medicine and treated Ms. Harris a total of five times after
the ShopKo accident. He testified that he could not conclude that
the ShopKo incident was the cause of Ms. Harris’s pain, stating
that he “just report[s] the news” and “do[esn’t] know where [the
pain] comes from.” He testified that the results of Ms. Harris’s
MRI and x-rays were “normal” and that her sacroiliac joint looked
“fairly normal.” He then testified that a sign of degenerative disc
disease is an annular tear. Dr. Colledge believed that Ms. Harris
had “an annular tear or . . . traumatized the disc complex” in her
back and that “she had some trauma.” He also testified that
Ms. Harris’s questionable sciatica in 2002 could potentially play a
role in her current pain. Ms. Harris’s counsel pointed out on cross-
examination that the radiologists disagreed as to whether
Ms. Harris had an annular tear.
    ¶11 Dr. Colledge further testified that Ms. Harris had back
pain consistent with degenerative disc disease. He acknowledged
that facet disease can be caused by a single incident of trauma and
that it can also be “brought to light” by trauma. But he believed
that Ms. Harris “probably ha[d] a component of” both
degenerative disc disease and facet disease or an aggravation of
both. Moreover, Dr. Colledge testified that degenerative disc
disease can be asymptomatic and that a traumatic incident can
cause it “to go from more of an asymptomatic to symptomatic
state.” Finally, he testified that Ms. Harris’s pain is still
“extraordinary” and “more than what [he] would usually see” for
an annular tear or facet disease after nine months. He thought

                                 4
                        Cite as: 2013 UT 34
                       Opinion of the Court
Ms. Harris’s use of narcotics and her involvement in the present
lawsuit could be delaying her recovery.
   ¶12 At the close of trial, the district court instructed the jury
concerning “[a]ggravation of symptomatic preexisting conditions”
(Apportionment Instruction). The Apportionment Instruction
read as follows:
       If Plaintiff had a physical, emotional, or mental
       condition before the time of the March 29, 2006
       incident, she is not entitled to recover damages for
       that condition or disability. However, Plaintiff is
       entitled to recover damages for any aggravation of
       the pre-existing condition that was caused by
       Defendant’s fault, even if Plaintiff’s pre-existing
       condition made her more vulnerable to physical or
       emotional harm than the average person. This is true
       even if another person may not have suffered any
       harm from the event at all.
       When a pre-existing condition makes the damages
       from injuries greater than they would have been
       without the condition, it is your duty to try to
       determine what portion of the physical, emotional or
       mental harm to Plaintiff was caused by the pre-
       existing condition and what portion was caused by
       the March 29, 2006 fall.
       If you are not able to make such an apportionment,
       then you must conclude that the entire physical,
       emotional and mental harm to Plaintiff was caused
       by Defendant’s fault.
    ¶13 Ms. Harris objected to the Apportionment Instruction
because it “talks about an aggravation of symptomatic preexisting
conditions, and . . . the evidence in this case does not support that
finding.” Ms. Harris also objected that there was no expert
testimony to guide the jury on how to apportion damages. The
court overruled her objections because “Dr. Colledge testified that
[the ShopKo accident] may have aggravated a degenerative disc
disorder[,] [s]o there is evidence of a preexisting condition.”




                                 5
                          HARRIS v. SHOPKO
                         Opinion of the Court
    ¶14 Ms. Harris requested $72,777.34 for past and future
medical expenses.1 Although the jury found ShopKo negligent, it
awarded her only $25,000 for those expenses, plus $1,000 in
noneconomic damages.2 Ms. Harris filed a motion for a new trial,
or, in the alternative, additur of damages. The trial court denied
her motion. Ms. Harris appealed.
    ¶15 The court of appeals reversed and remanded for a new
trial. Relying on Biswell v. Duncan,3 it held that the trial court erred
in giving the Apportionment Instruction because there was no
evidence that Ms. Harris’s preexisting conditions were
symptomatic at the time she fell at ShopKo.4 The court also found
that the Apportionment Instruction prejudiced Ms. Harris because
“had the [improper] instruction [not] been given, the jury might
have awarded more damages.”5 We granted ShopKo’s petition for
certiorari and have jurisdiction pursuant to section 78A-3-
102(3)(a) of the Utah Code.
                     STANDARD OF REVIEW
    ¶16 “On certiorari we review the decision of the court of
appeals, not the decision of the trial court. In doing so, we review
for correctness, giving the court of appeals’ conclusions of law no
deference.”6
                             ANALYSIS
   ¶17 The court of appeals reversed the jury’s award and
remanded for a new trial on the ground that the trial court erred
in giving the Apportionment Instruction. On certiorari, ShopKo
argues that the court of appeals applied the wrong legal standard
when it concluded that preexisting conditions must be
symptomatic on the day of the accident in order to justify


   1 Harris v. ShopKo Stores, Inc., 2011 UT App 329, ¶ 11, 263 P.3d
1184.
   2   Id.
   3   742 P.2d 80 (Utah Ct. App. 1987).
   4   Harris, 2011 UT App 329, ¶¶ 14, 24.
   5 Id. ¶ 25 (alterations in original) (internal quotation marks
omitted).
   6Grand Cnty. v. Rogers, 2002 UT 25, ¶ 6, 44 P.3d 734 (internal
quotation marks omitted).


                                   6
                            Cite as: 2013 UT 34
                            Opinion of the Court
apportioning damages. ShopKo also argues that the court of
appeals erred in holding that there was insufficient evidence to
support giving the Apportionment Instruction.
    ¶18 We decline to adopt the legal standard applied by the
court of appeals because it requires a bright-line approach that is
inconsistent with the principle of proximate cause, which should
be the overarching and guiding principle in the analysis. But we
nevertheless agree that the Apportionment Instruction was
improper because the evidence at trial failed to provide a
nonarbitrary basis for the jury to apportion damages. We
therefore affirm the court of appeals’ decision to order a new trial
in this case.
  I. WE DECLINE TO ADOPT THE COURT OF APPEALS’
APPROACH OF REQUIRING PREEXISTING CONDITIONS TO
 BE SYMPTOMATIC ON THE DAY OF THE ACCIDENT IN
 ORDER FOR AN APPORTIONMENT INSTRUCTION TO BE
                     PROPER
    ¶19 In deciding whether the Apportionment Instruction was
properly given, the court of appeals determined that the “crucial
question” in the analysis is whether the preexisting condition was
symptomatic on the date of the injury.7 Under the court’s
approach, a preexisting condition provides a basis for
apportionment if, but only if, it is symptomatic on the date of the
tortious conduct.8 Thus, in the eyes of the court, “a victim with
latent, dormant, or otherwise asymptomatic pre-existing
conditions stands on equal footing with a victim with no pre-
existing conditions.”9 In other words, under the court’s analysis, a
preexisting condition that is asymptomatic on the date of the
accident cannot justify any reduction in damages.
   ¶20 In assigning determinative effect to whether a preexisting
condition is symptomatic or asymptomatic on the injury date, the
court of appeals relied on its decision in Biswell v. Duncan.10
Biswell involved a plaintiff who had a preexisting condition that


   7 Harris v. ShopKo Stores, Inc., 2011 UT App 329, ¶ 23, 263 P.3d
1184.
   8   Id. ¶¶ 23, 27.
   9   Id. ¶ 17.
   10   Id. ¶¶ 17, 22–24.


                                     7
                           HARRIS v. SHOPKO
                         Opinion of the Court
she claimed had been “resolved” and therefore did not cause pain
prior to the accident.11 The court stated that “when a defendant’s
negligence aggravates . . . a latent, dormant, or asymptomatic
condition, . . . the defendant is liable . . . for the full amount of
damages which ensue.”12 The court elaborated:
         [W]hen a latent condition itself does not cause pain,
         but that condition plus an injury brings on pain by
         aggravating the pre-existing condition, then the
         injury, not the dormant condition, is the proximate
         cause of the pain and disability. A plaintiff,
         therefore, is entitled to recover all damages which
         actually and necessarily follow the injury.13
   ¶21 The court of appeals quoted this language from Biswell in
the instant case to support its conclusion that when a condition is
asymptomatic on the date of the accident, the negligence will be
deemed the proximate cause of the entire injury, and the
preexisting condition will be disregarded.14 Thus, by determining
that Ms. Harris’s conditions were asymptomatic on the date of the
accident and that the Apportionment Instruction was improper,
the court assumed that Ms. Harris’s preexisting conditions could
not have caused any portion of her pain and injury.
    ¶22 That the court of appeals would adopt this approach is
certainly understandable given that other jurisdictions have
followed a similar approach,15 but we decline to adopt it. We
conclude that our case law—which recognizes the central role
proximate cause must play in tort law—is inconsistent with such a
narrow, bright-line approach.


   11   742 P.2d 80, 88 (Utah Ct. App. 1987).
   12   Id.
   13   Id.
   14   Harris, 2011 UT App 329, ¶ 23.
   15 See, e.g., Sleeth v. Louvar, 659 N.W.2d 210, 213–16 (Iowa 2003)
(finding error in instructing the jury on aggravation where there
was no evidence that plaintiff’s preexisting arthritis was
symptomatic prior to the accident at issue). But see id. at 217
(Carter, J., dissenting) (arguing that, given the evidence in the
case, the jury should have been able to decide whether some or all
of plaintiff’s pain would have occurred even absent the accident).


                                   8
                           Cite as: 2013 UT 34
                          Opinion of the Court
    ¶23 In Brunson v. Strong, we recognized that “one who injures
another takes him as he is.”16 Thus, a plaintiff is entitled to recover
for all harm that is proximately caused by the defendant’s
negligence, “even if a given plaintiff is more vulnerable to injury
than others.”17 But this principle, commonly known as the
eggshell plaintiff doctrine, in no way bars consideration of other
relevant potential sources of a plaintiff’s pain in determining the
extent of damage proximately caused by the defendant.
    ¶24 Indeed, we further recognized in Brunson that although
an injured party is taken “as he is, nevertheless the plaintiff may
not recover damages for any pre-existing condition or disability
she may have had which did not result from any fault of the
defendant.”18 And while “she is entitled to recover damages for
any injury she suffered, including any aggravation . . . of such a
pre-existing condition,” she may only do so to the extent that the
aggravation “was proximately caused by the defendant’s negligence.”19
Moreover, in Tingey v. Christensen, we stated that “if the jury can
find a reasonable basis for apportioning damages between a
preexisting condition and a subsequent tort, it should do so.”20
   ¶25 These cases highlight the fundamental aim in deciding
damages: “to restore the injured party to the position he would
have been in had it not been for the wrong of the other party.”21
Proximate cause plays a central role in determining the precise
extent of the defendant’s liability and, in turn, what the plaintiff’s
position would have been absent the defendant’s negligence.22


   16   Brunson v. Strong, 412 P.2d 451, 453 (Utah 1966).
   17   Ryan v. Gold Cross Servs., Inc., 903 P.2d 423, 428 (Utah 1995).
   18 Brunson, 412 P.2d at 453 (emphasis added) (footnote
omitted).
   19   Id. (emphasis added).
   20   1999 UT 68, ¶ 15, 987 P.2d 588.
   21   Park v. Moorman Mfg. Co., 241 P.2d 914, 920 (Utah 1952).
   22  See Raab v. Utah Ry. Co., 2009 UT 61, ¶ 22, 221 P.3d 219
(“[T]he ‘legal cause’ inquiry focuses on the question of whether
liability should attach to a particular cause in fact.”); id. ¶ 35
(“[A]ssessment of legal responsibility for a cause in fact of an
injury is the raison d’etre of the proximate cause requirement.”);
Williams v. Barber, 765 P.2d 887, 889 (Utah 1988) (“With respect to
                                                      (Continued)
                                  9
                         HARRIS v. SHOPKO
                       Opinion of the Court
    ¶26 The eggshell plaintiff doctrine does not alter this aim. It
has never required tortfeasors to compensate plaintiffs for
damages that the tortfeasors’ negligence did not proximately
cause.23 In our view, however, the court of appeals’ narrow,
bright-line approach to the eggshell plaintiff doctrine is
inconsistent with this aim of awarding damages. An
asymptomatic preexisting condition may well be an independent
contributor to a plaintiff’s pain and injury, which was also
proximately caused to some degree by a tortfeasor’s negligence.24
But the court of appeals’ approach would prevent the jury from
apportioning damages between the preexisting condition and the
negligence simply because the preexisting condition was not
symptomatic on the date of the accident. In our view, this result is
potentially arbitrary and risks holding defendants liable for more
than they proximately caused in damages. We accordingly
conclude that whether a preexisting condition is symptomatic or
asymptomatic on the date of the accident is not the determinative
factor in granting an apportionment instruction.25




tort liability generally, a finding of proximate cause must be made
by the trier of fact before an award for damages is granted.”).
   23 See, e.g., Gibson v. Cnty. of Washoe, Nev., 290 F.3d 1175, 1192–
93 (9th Cir. 2002) (discussing the eggshell plaintiff doctrine and
recognizing that “[t]he defendant of course is liable only for the
extent to which the defendant’s conduct has resulted in an
aggravation of the pre-existing condition, and not for the
condition as it was” (internal quotation marks omitted)).
   24 See, e.g., Maurer v. United States, 668 F.2d 98, 100 (2d Cir.
1981) (per curiam) (stating that “when a plaintiff has a preexisting
condition that would inevitably worsen, a defendant causing
subsequent injury is entitled to have the plaintiff’s damages
discounted to reflect the proportion of damages that would have
been suffered even in the absence of the subsequent injury”); see
also Sauer v. Burlington N. R.R. Co., 106 F.3d 1490, 1495 (10th Cir.
1996) (citing cases that recognize this proposition).
   25 We also note that, to the extent that the court of appeals’
approach requires evidence of symptoms on the precise date of
the injury, it is inconsistent with our decision in Tingey, where we
held that evidence of pain from a preexisting condition twenty-
five days before an accident was sufficient to justify a jury’s
                                                         (Continued)
                                   10
                            Cite as: 2013 UT 34
                            Opinion of the Court
    ¶27 While we reaffirm the jury’s duty to apportion damages if
the evidence supports doing so, we recognize that it is rarely easy
to determine the causal contribution of a preexisting condition to
a plaintiff’s pain and injury. The “[o]bjective symptoms and the
physical basis of . . . ailment[s] are often difficult to discover,
analyze and demonstrate to others.”26 If the preexisting condition
is asymptomatic at the time of the tortious conduct, the analysis
will be even more difficult. But the “evaluation and the conclusion
to be drawn [from the evidence] is peculiarly within the province
of the jury.”27 Indeed, proximate cause—although often a thorny
issue—is generally a question of fact for the jury to decide.28
    ¶28 We are also confident that our case law already provides
sufficient protection for eggshell-type plaintiffs even without the
court of appeals’ bright-line approach. In Tingey, we recognized
that “a tortfeasor should bear the burden of uncertainty in the
amount of a tort victim’s damages.”29 We accordingly held that
while a jury should apportion if it can, “it should find that the
tortfeasor is liable for the entire amount of damages” if it “finds it
impossible to apportion.”30 Thus, the burden is on the defendant
to demonstrate that apportionment is possible where there is any
uncertainty.31

conclusion that the preexisting condition was the cause of harm
suffered after the accident. 1999 UT 68, ¶ 18.
   26   Brunson, 412 P.2d at 453.
   27   Id.
   28 Crestwood Cove Apartments Bus. Trust v. Turner, 2007 UT 48,
¶ 31, 164 P.3d 1247; Harline v. Barker, 912 P.2d 433, 439 (Utah
1996). The two circumstances in which proximate cause may be
decided as a matter of law are “(i) when the facts are so clear that
reasonable persons could not disagree about the underlying facts
or about the application of a legal standard to the facts, and
(ii) when the proximate cause of an injury is left to speculation so
that the claim fails as a matter of law.” Crestwood Cove, 2007 UT 48,
¶ 32 (internal quotation marks omitted).
   29   1999 UT 68, ¶ 14.
   30   Id. ¶ 15.
   31  See Robinson v. All-Star Delivery, Inc., 1999 UT 109, ¶ 13 n.3,
992 P.2d 969 (discussing a tortfeasor’s liability when the evidence
at trial is uncertain as to apportionability of damages).

                                    11
                            HARRIS v. SHOPKO
                          Opinion of the Court
    ¶29 Finally, we emphasize that our decision today is not an
invitation for tortfeasors to dredge up every physical injury or
defect a victim has ever had in an attempt to reduce liability.
Evidence of preexisting conditions must be relevant to the pain or
injury at issue and must also overcome other pertinent
evidentiary hurdles in order to be admissible.32 If there is no
evidence that a particular preexisting condition is relevant to the
plaintiff’s pain or injury, evidence of that condition should not be
admitted.
    ¶30 Because a jury should apportion damages if the evidence
indicates that the defendant’s conduct was not the sole proximate
cause of the plaintiff’s injury, we decline to adopt the court of
appeals’ bright-line approach of focusing on whether the
condition was asymptomatic or symptomatic on the date of the
accident. We next consider whether there was sufficient evidence
to support giving the Apportionment Instruction in this case.
II. THE APPORTIONMENT INSTRUCTION WAS ERRONEOUS
BECAUSE THE EVIDENCE AT TRIAL DID NOT PROVIDE THE
 JURY WITH A NONARBITRARY BASIS FOR APPORTIONING
                    DAMAGES
   ¶31 The court of appeals concluded that there was insufficient
evidence to support the Apportionment Instruction.33 As
discussed above, this conclusion was a product of the court’s
bright-line approach to symptomatic and asymptomatic
preexisting conditions, which we have declined to adopt. We
must now consider whether the evidence at trial supported the
Apportionment Instruction. While we recognize that there was, as
the trial court found, expert testimony that Ms. Harris had a
preexisting condition, we conclude that this testimony alone was
insufficient to support the Apportionment Instruction because it
did not address the extent to which Ms. Harris’s condition may
have contributed to her injury and pain.34



   32   See, e.g., UTAH R. EVID. 401, 402, 403.
   33   Harris v. ShopKo Stores, Inc., 2011 UT App 329, ¶ 24, 263 P.3d
1184.
   34 Ms. Harris also argues that we can affirm the court of
appeals’ decision on the alternative ground that the trial court
improperly instructed the jury to reduce future damages to
present value. We decline to reach this issue given our conclusion
                                                      (Continued)
                                12
                           Cite as: 2013 UT 34
                         Opinion of the Court
    ¶32 “The jury is entrusted to resolve all relevant questions of
fact presented to the court,” including “apportionment.”35
Nevertheless, the jury must have a reasonable basis for
apportioning damages,36 and apportionment may not be based on
“pure speculation.”37 A jury instruction on apportionment,
therefore, requires that there be some nonarbitrary evidentiary
basis for the jury to apportion damages.38
    ¶33 In other contexts, we have declined to require expert
testimony on apportionment. In fact, we have held that such
expert testimony should be precluded in certain circumstances.
For example, in Steffensen v. Smith’s Management Corp., a
comparative negligence case, we held that the trial court did not
abuse its discretion by excluding expert testimony on
apportioning fault because the testimony would not have been
“helpful to the fact finder” and “the apportionment of


that there was insufficient evidence to support the Apportionment
Instruction.
   35 Little Am. Ref. Co. v. Leyba, 641 P.2d 112, 114 (Utah 1982); see
also Anderson v. Bradley, 590 P.2d 339, 342 (Utah 1979) (“[I]t is the
jury’s prerogative to decide questions of [comparative]
negligence.”).
   36 See Egbert v. Nissan Motor Co., 2010 UT 8, ¶ 37, 228 P.3d 737
(“[F]or a jury to apportion relative fault between two parties, the
jury, of necessity, must have sufficient evidence of the culpability of
each party to make that apportionment.” (internal quotation
marks omitted)); see also Osuala v. Olsen, 609 P.2d 1325, 1326 (Utah
1980) (“There is substantial, credible evidence here, together with
reasonable inference to be drawn therefrom, by which the Court,
as factfinder, could apportion the negligence between the parties
as it did.”); Lamkin v. Lynch, 600 P.2d 530, 531–32 (Utah 1979)
(refusing to disturb an apportioned jury award because “the jury
could reasonably conclude” from the evidence that the
apportionment was appropriate); Anderson, 590 P.2d at 342
(“From the record it appears that the jury reasonably concluded
that plaintiff and defendant were equally negligent, and it is the
jury’s prerogative to decide questions of driver’s and pedestrian’s
negligence.”).
   37   Egbert, 2010 UT 8, ¶ 37.
   38   Tingey v. Christensen, 1999 UT 68, ¶ 15, 987 P.2d 588.


                                   13
                         HARRIS v. SHOPKO
                       Opinion of the Court
negligence . . . was exclusively the jury’s responsibility.”39 But
finding fault is normally an exercise in common sense of which
jurors and experts are equally capable.40 Thus, the nonarbitrary
basis for apportioning damages in cases like Steffensen can be
found in the jury’s common experience.
   ¶34 This is often not true when allocating causation between
preexisting pathologies and a subsequent accident. Where
apportionment depends on the competing causal influences of a
defendant’s negligence and a preexisting medical condition, as it
does in this case, common experience is a poor substitute for
expert guidance.41 This is because the average lay juror is ill-
equipped to sift through complicated medical evidence and come
to a nonspeculative apportionment decision.42 In cases like this,
expert testimony may be the jury’s only guide as to whether
apportionment is proper and, if so, to what extent.
    ¶35 In the instant case, we conclude that expert testimony
allocating causation between Ms. Harris’s preexisting conditions
and her fall at ShopKo was necessary in order for an


   39  862 P.2d 1342, 1347–48 (Utah 1993); see also UTAH R. EVID.
702(a) (“[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 the expert’s scientific, technical, or
other specialized knowledge will help the trier of fact to understand
the evidence or to determine a fact in issue.” (emphasis added)).
   40 See Leyba, 641 P.2d at 114 (stating that apportionment of fault
is entrusted to juries).
   41 See Martin v. Owens-Corning Fiberglas Corp., 528 A.2d 947, 950
(Pa. 1987) (plurality opinion) (“[C]ommon sense and common
experience possessed by a jury do not serve as substitutes for
expert guidance, and it follows that any apportionment by the
jury in this case was a result of speculation and conjecture and
hence, improper.”); Lee v. Pittsburgh Corning Corp., 616 A.2d 1045,
1048 (Pa. Super. Ct. 1992) (same).
   42 Cf. Bowman v. Kalm, 2008 UT 9, ¶ 7, 179 P.3d 754 (stating that
the “general requirement in medical malpractice cases that the
element of proximate cause be supported by expert testimony” is
grounded in the idea that “the causal link between the negligence
and the injury [is] usually not within the common knowledge of
the lay juror”).


                                 14
                        Cite as: 2013 UT 34
                       Opinion of the Court
apportionment instruction to be given. The evidence supports a
reasonable inference that Ms. Harris had previously suffered
injuries in car accidents and that she had a number of preexisting
conditions at the time of her fall. For example, Dr. Colledge, who
testified for ShopKo, stated that he believed Ms. Harris had an
annular tear, which could be a sign of degenerative disc disease.
He also testified that Ms. Harris’s back pain was consistent with
degenerative disc disease and suggested that her facet joint
syndrome may have predated, and been aggravated by, her fall at
ShopKo.
    ¶36 And there is also testimony indicating that these
preexisting conditions contributed to Ms. Harris’s pain and that
they would have caused similar symptoms even in the absence of
her fall at ShopKo. Dr. Rosenthal testified that the facet joint
syndrome, which he had diagnosed Ms. Harris with after her fall,
can be caused by degenerative disc disorder. Dr. Scuderi testified
that it was “not unusual” for somebody of “Ms. Harris’s age to
have some neck and back pain.” And Dr. Colledge testified that
degenerative disc disease and Ms. Harris’s prior “questionable
sciatica” could have contributed to her symptoms.
    ¶37 But while this testimony suggests some connection
between Ms. Harris’s preexisting conditions and her current pain,
there is no expert testimony in the record on the extent to which
her conditions contributed to her pain, if at all. In fact,
Dr. Colledge refused to offer such an opinion, stating that he “just
report[s] the news” and “do[esn’t] know where [the pain] comes
from.” He did testify that Ms. Harris “probably has a component
of” both degenerative disc disease and facet disease or an
aggravation of both. But this testimony does not provide a relative
comparison between the proposed causes of Ms. Harris’s pain.
Without such testimony, the jury would have had to speculate as
to any basis for apportioning damages, especially in light of
Ms. Harris’s expert testimony indicating that her fall at ShopKo
caused her injury. We therefore conclude that there was
insufficient evidence to support the Apportionment Instruction in
this case. On remand, an apportionment instruction will be proper
only if there is adequate expert testimony that Ms. Harris’s
preexisting back condition contributed to her injury and, if so, to
what extent.




                                15
                          HARRIS v. SHOPKO
                        Opinion of the Court
    ¶38 Although expert testimony allocating causation is
necessary for an apportionment instruction on remand, the
testimony need not opine on the exact percentage, if any, of the
injury attributable to Ms. Harris’s preexisting conditions.43 In an
ideal world, an expert would provide a precise estimation (e.g.,
“Fifty percent of the injury is attributable to the preexisting
condition.”). But we must account for the reality of medical
uncertainty. An apportionment instruction will not be precluded
if the testimony presents a reasonable range of percentages (e.g.,
“Forty to sixty percent of the injury is attributable to the
preexisting condition.”) or a useful nonnumeric description (e.g.,
“The vast majority of the injury is attributable to the preexisting
condition.”).44 The determinative question is whether the expert
testimony has supplied the jury with a nonarbitrary basis for
apportioning damages.
   ¶39 Finally, ShopKo argues that even if the Apportionment
Instruction was erroneous, it was harmless because the jury may
have awarded Ms. Harris less than she requested on the ground
that some of her medical care was not reasonably necessary. We
disagree. An erroneous jury instruction is prejudicial if, taken “in
context” with “the jury instructions as a whole,”45 “it misadvised
or misled the jury on the law.”46 The law on apportionment to



   43 See Egbert, 2010 UT 8, ¶ 37 (“sufficient evidence is not pure
speculation, but neither does it require . . . precise, specific
evidence” (internal quotation marks omitted)); see also Sauer v.
Burlington N. R.R. Co., 106 F.3d 1490, 1494 (10th Cir. 1996) (“The
extent to which an injury is attributable to a preexisting condition
or prior accident need not be proved with mathematical precision
or great exactitude. The evidence need only be sufficient to permit
a rough practical apportionment.”).
   44 See Egbert, 2010 UT 8, ¶ 38 (“This apportionment may of
course . . . be a rough apportionment” (internal quotation marks
omitted)).
   45 Jensen v. Intermountain Power Agency, 1999 UT 10, ¶ 16, 977
P.2d 474 (internal quotation marks omitted).
   46 Butler v. Naylor, 1999 UT 85, ¶ 10, 987 P.2d 41; see also Jensen,
1999 UT 10, ¶ 16 (“[I]f the jury instructions as a whole fairly
instruct the jury on the applicable law, reversible error does not
arise merely because one jury instruction, standing alone, is not as
                                                         (Continued)
                                 16
                          Cite as: 2013 UT 34
                         Opinion of the Court
preexisting conditions was inapplicable because, as we have
explained, the evidence did not provide the jury a nonarbitrary
basis to apportion damages. Nothing in the jury instructions as a
whole cured the erroneous instruction. Indeed, the
Apportionment Instruction went so far as to impart a “duty” for
the jury to apportion damages in this case whereas we have
concluded that there was nothing beyond a speculative basis for
doing so.
    ¶40 We also note, as did the court of appeals,47 that we are
obviously unable to know the precise basis of the jury’s award.
Nevertheless, given the substantial testimony at trial concerning
Ms. Harris’s preexisting conditions, ShopKo’s arguments at trial
concerning apportionment,48 and the Apportionment Instruction
itself, we find it “reasonably likely” that the jury apportioned
damages to Ms. Harris’s preexisting conditions.49 Therefore, our
“confidence in the jury’s verdict is undermined” and reversal is
required.50
                            CONCLUSION
    ¶41 The court of appeals’ bright-line approach to analyzing
preexisting conditions, focusing exclusively on whether a
condition was symptomatic or asymptomatic on the date of the
accident, risks holding defendants liable for more damages than
they proximately caused. We therefore decline to adopt it. We also
conclude that the Apportionment Instruction was erroneous and
prejudicial because (a) the evidence failed to supply the jury with
a nonarbitrary basis for apportioning damages, and (b) there is a
reasonable likelihood the jury apportioned damages. On the facts
of Ms. Harris’s case, an apportionment instruction requires expert
testimony on the portion of the plaintiff’s injury that is

accurate as it might have been.” (emphasis added) (internal
quotation marks omitted)).
   47   Harris, 2011 UT App 329, ¶ 25.
   48  At closing argument, counsel for ShopKo argued that
Ms. Harris was “asking to be compensated for conditions that
existed before the accident, and under the law that’s not proper.”
   49 See Cal Wadsworth Constr. v. City of St. George, 898 P.2d 1372,
1378–79 (Utah 1995) (“An error is harmful if it is reasonably likely
that the error affected the outcome of the proceedings.”).
   50   Tingey, 1999 UT 68, ¶ 16.


                                    17
                        HARRIS v. SHOPKO
                      Opinion of the Court
attributable to her preexisting conditions. Accordingly, we affirm
and remand to the court of appeals to order a new trial consistent
with this opinion.




                               18
