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                                  Nebraska Supreme Court A dvance Sheets
                                          302 Nebraska R eports
                                               PITTS v. GENIE INDUS.
                                                  Cite as 302 Neb. 88




                        Trevor Pitts       and R ebekah Pitts, a married couple,
                                 appellants, and   H aco Electric Company,
                                  Incorporated, a Nebraska corporation,
                                    appellee, v. Genie I ndustries, I nc., a
                                     Washington corporation, appellee.
                                                   ___ N.W.2d ___

                                        Filed January 18, 2019.   No. S-18-219.

                1.	 Summary Judgment: Appeal and Error. An appellate court reviews
                    the district court’s grant of summary judgment de novo, viewing the
                    record in the light most favorable to the nonmoving party and drawing
                    all reasonable inferences in that party’s favor.
                2.	 Trial: Expert Witnesses: Appeal and Error. An appellate court reviews
                    de novo whether the trial court applied the correct legal standards for
                    admitting an expert’s testimony. But a trial court’s ruling in receiving
                    or excluding an expert’s testimony which is otherwise relevant will be
                    reversed only when there has been an abuse of discretion.
                3.	 Judges: Words and Phrases. A judicial abuse of discretion exists when
                    a judge, within the effective limits of authorized judicial power, elects
                    to act or refrain from acting, but the selected option results in a deci-
                    sion which is untenable and unfairly deprives a litigant of a substantial
                    right or a just result in matters submitted for disposition through a judi-
                    cial system.
                4.	 Summary Judgment: Appeal and Error. An appellate court will
                    affirm a lower court’s grant of summary judgment if the pleadings and
                    admitted evidence show that there is no genuine issue as to any material
                    facts or as to the ultimate inferences that may be drawn from those facts
                    and that the moving party is entitled to judgment as a matter of law. In
                    the summary judgment context, a fact is material only if it would affect
                    the outcome of the case.
                5.	 Products Liability: Actions: Negligence. In a products liability cause
                    of action based on strict liability in tort, the central question involves
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              Nebraska Supreme Court A dvance Sheets
                      302 Nebraska R eports
                            PITTS v. GENIE INDUS.
                               Cite as 302 Neb. 88

     the quality of the manufactured product, that is, whether the product was
     unreasonably dangerous.
 6.	 Products Liability: Words and Phrases. “Unreasonably dangerous”
     means that the product has a propensity for causing physical harm
     beyond that which could be contemplated by the ordinary user or
     consumer.
 7.	 Products Liability: Proof. In a products liability action based on defect,
     a plaintiff must prove by a preponderance of the evidence that (1) the
     defendant placed the product on the market for use and knew, or in the
     exercise of reasonable care should have known, that the product would
     be used without inspection for defects; (2) the product was in a defec-
     tive condition when it was placed on the market and left the defendant’s
     possession; (3) the defect is the proximate or a proximately contributing
     cause of the plaintiff’s injury sustained while the product was being
     used in a way and for the general purpose for which it was designed and
     intended; (4) the defect, if existent, rendered the product unreasonably
     dangerous and unsafe for its intended use; and (5) the plaintiff’s dam-
     ages were a direct and proximate result of the alleged defect.
 8.	 Products Liability: Negligence: Proximate Cause: Proof. To establish
     proximate cause in a products liability action, the plaintiff must meet
     three basic requirements: (1) Without the defect, the injury would not
     have occurred, commonly known as the “but for” rule or “cause in fact”;
     (2) the injury was a natural and probable result of the defect; and (3)
     there was no efficient intervening cause.
 9.	 Expert Witnesses: Testimony. Findings of fact as to technical mat-
     ters beyond the scope of ordinary experience are not warranted in the
     absence of expert testimony supporting such findings.
10.	 Trial: Expert Witnesses. With respect to the requirement of expert tes-
     timony, the test is whether the particular issue can be determined from
     the evidence presented and the common knowledge and usual experi-
     ence of the fact finders.
11.	 Summary Judgment. Conclusions based on guess, speculation, conjec-
     ture, or a choice of possibilities do not create material issues of fact for
     purposes of summary judgment.
12.	 Rules of Evidence: Expert Witnesses. When a court is faced with a
     decision regarding the admissibility of expert opinion evidence, the trial
     judge must determine at the outset, pursuant to the evidence rule govern-
     ing expert witness testimony, whether the expert is proposing to testify
     to (1) scientific, technical, or other specialized knowledge that (2) will
     assist the trier of fact to understand or determine a fact in issue.
13.	 Courts: Expert Witnesses. In evaluating expert opinion testimony
     under Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579,
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                Nebraska Supreme Court A dvance Sheets
                        302 Nebraska R eports
                              PITTS v. GENIE INDUS.
                                 Cite as 302 Neb. 88

       113 S. Ct. 2786, 125 L. Ed. 2d 469 (1993), and Schafersman v. Agland
       Coop, 262 Neb. 215, 631 N.W.2d 862 (2001), where such testimony’s
       factual basis, data, principles, methods, or their application are called
       sufficiently into question, the trial judge must determine whether the
       testimony has a reliable basis in the knowledge and experience of the
       relevant discipline.
14.	   Expert Witnesses: Words and Phrases. Expert testimony based upon
       possibility or speculation is insufficient to establish causation; it must be
       stated as being at least probable, in other words, more likely than not.
15.	   Negligence: Products Liability. The malfunction theory is based on the
       same principle underlying res ipsa loquitur, which permits a fact finder
       to infer negligence from the circumstances of the incident, without
       resort to direct evidence of the wrongful act.
16.	   Products Liability: Proof. Under the malfunction theory, also some-
       times called the indeterminate defect theory or general defect theory, a
       plaintiff may prove a product defect circumstantially, without proof of
       a specific defect, when (1) the incident causing the harm was of a kind
       that would ordinarily occur only as a result of a product defect and (2)
       the incident was not, in the particular case, solely the result of causes
       other than a product defect existing at the time of sale or distribution.
17.	   ____: ____. The malfunction theory simply provides that it is not nec-
       essary for the plaintiff to establish a specific defect so long as there is
       evidence of some unspecified dangerous condition or malfunction from
       which a defect can be inferred—the malfunction itself is circumstantial
       evidence of a defective condition.
18.	   Products Liability: Proximate Cause: Damages: Proof. The malfunc-
       tion theory does not alter the basic elements of the plaintiff’s burden of
       proof and is not a means to prove proximate cause or damages.
11.	   Products Liability: Strict Liability: Proof. The malfunction theory is
       applicable in a strict liability manufacturing defect claim.
12.	   Products Liability: Proof. The malfunction theory is not available
       when specific defects are alleged.

   Appeal from the District Court for Lancaster County: Darla
J. Ideus, Judge. Affirmed.
   Peter C. Wegman, Mark R. Richardson, and Alyssa P. Martin,
of Rembolt Ludtke, L.L.P., and John W. Ballew, Jr., of Ballew
Hazen, P.C., L.L.O., for appellants.
   Michael L. Moran, of Engles, Ketcham, Olson & Keith,
P.C., for appellee Haco Electric Company, Incorporated.
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           Nebraska Supreme Court A dvance Sheets
                   302 Nebraska R eports
                      PITTS v. GENIE INDUS.
                         Cite as 302 Neb. 88

   Michael F. Coyle and Timothy J. Thalken, of Fraser Stryker,
P.C., L.L.O., for appellee Genie Industries, Inc.
  Heavican, C.J., Miller-Lerman, Cassel, Stacy, Funke,
Papik, and Freudenberg, JJ.
  Freudenberg, J.
                      NATURE OF CASE
   An electrician was injured when an aerial lift malfunc-
tioned and tipped over while the electrician was working
approximately 30 feet in the air on the lift’s raised platform.
After sustaining serious injuries, the electrician brought strict
liability claims, negligence claims, and an implied warranty
claim against Genie Industries, Inc. (Genie), the manufac-
turer and designer of the lift. Genie moved for summary
judgment as to all of the electrician’s claims and sought
to exclude the electrician’s expert opinions on the issues
of unreasonably dangerous conditions, defect, causation, and
alternative design. Following a hearing, the district court par-
tially granted Genie’s motion to exclude expert testimony and
granted Genie’s motion for summary judgment on all claims.
The electrician appeals.
                            FACTS
                          A erial Lift
   Genie manufactured an aerial lift named Genie model
“TZ-34/20.” In order to operate the lift, an operator stands
on a platform, or “bucket” or “basket,” and the platform is
raised and lowered. The platform is raised and lowered by
an extension of the lift referred to as a “boom.” The lift sits
atop of four outriggers that can be retracted when the lift is
being transported. The outriggers are intended to extend, make
contact with the ground, and raise the lift off the ground in a
level manner.
   The user operates the lift by pressing buttons on one of
two control panels: (1) a ground control panel that operates
the outriggers, boom, and platform and (2) a platform control
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           Nebraska Supreme Court A dvance Sheets
                   302 Nebraska R eports
                      PITTS v. GENIE INDUS.
                         Cite as 302 Neb. 88

panel located directly on the platform that operates only the
boom and the platform. There is also a key switch located at
the platform controls that selects which of these two controls
will operate. For example, when the key switch is turned to
the platform setting, the ground controls will not operate. In
theory, an operator standing on the platform should not be able
to move or control the outriggers by pressing buttons on the
platform control panel. This mechanism was designed to avoid
destabilization while an operator is on the platform.
    The lift in question was sold by Genie to Nebraska Machinery
Company (Nebraska Machinery) in May 2011. Over the next
few years, a number of repairs were performed on the lift.
According to Nebraska Machinery’s work orders, the lift was
first repaired in August 2011, 4 months after the sale, when the
“limit switch” failed, which caused the lift to become incapable
of lowering. In the 2 years prior to the electrician’s accident,
there were approximately 30 total work orders for repairs on
this particular lift, several of which related to issues with the
“auto-leveling” system and the outriggers.
    Genie started manufacturing this type of lift in 2003 and has
made more than 4,600 of them. Genie is not aware of any other
lift falling over in the same manner on any other occasion.
During the end of the manufacturing process, Genie tested the
lift’s functions and determined that the tested movement func-
tions worked properly. Genie’s senior product safety manager
testified that the lift’s design was consistent with all relevant
national standards and that in his opinion, the lift’s design
used the best technology reasonably available at the time it
was made.
                             Accident
   In June 2013, Nebraska Machinery leased the lift to a gen-
eral contractor for use at a jobsite in Seward, Nebraska. Trevor
Pitts is an electrician and was working for an electrical sub-
contractor. On August 21, the lift tipped over while Pitts was
working on the platform approximately 30 feet in the air. Pitts
had used the lift without any problems for 10 days before the
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           Nebraska Supreme Court A dvance Sheets
                   302 Nebraska R eports
                      PITTS v. GENIE INDUS.
                         Cite as 302 Neb. 88

accident. On the day of the accident, other subcontractors had
used the lift less than an hour before the incident.
   There appeared to be electrical tape over a button on the
platform control panel, but Pitts did not know why the tape
was on the button or who put it there. According to Genie,
the button that was taped over was the button that levels the
platform when it is in the air. Genie argues that this indicates
that the leveling system was altered after the machine left
Genie’s possession.
   After the accident, bystanders who came to the scene saw
that the left rear outrigger was “retracted.” As a result of that
outrigger’s being shorter than the others, the lift was not level
and tipped over, causing Pitts’ injuries.
   Pitts and his wife brought several claims against Genie (and
two other parties, now dismissed) in the Lancaster County
District Court. These claims included three strict liability
claims for manufacturing and design defects and a failure to
warn, three negligence claims, one breach of implied warranty
claim, and a loss of consortium claim.
                   Dr. John Boye’s Testimony
   The Pittses’ sole expert was an electrical engineer, Dr.
John Boye. Boye is a professor emeritus in the University of
Nebraska-Lincoln electrical and computer engineering depart-
ment who holds a Ph.D. in electrical engineering. Along with
another electrical engineer, Boye also formed a small electrical
engineering consulting firm as a licensed electrical and com-
puter engineer with the state. Boye had never before examined,
used, repaired, or designed an aerial lift. He also had never
reviewed any other lift in the industry.
   In preparing his expert report, Boye reviewed video footage
from a November 2014 inspection that he did not attend. In
the video, at least 20 different malfunctions of the left outrig-
ger occurred. He also reviewed several photographs taken at
the time of the accident and from the 2014 inspection, some
technical documents, the work order history, depositions, and
a fuel log from Nebraska Machinery. The extensive work order
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           Nebraska Supreme Court A dvance Sheets
                   302 Nebraska R eports
                      PITTS v. GENIE INDUS.
                         Cite as 302 Neb. 88

history and fuel log indicated that the auto-leveling system
was not working correctly prior to the date of the accident.
   Boye reported that the photographs from the 2014 inspec-
tion showed the wiring inside the ground control panel was
“not well done.” He explained that the leads of the diodes were
not insulated and were very close together. Boye describes
a diode as an electrical device that allows current to flow in
one direction.
   Boye later participated in a physical inspection of the lift
in November 2015. In the year since the November 2014
inspection, the lift remained in the sole possession of Nebraska
Machinery. However, when Boye completed his 2015 inspec-
tion, the lift behaved differently than it did in 2014. In his
report, Boye explained that the lift clearly malfunctioned in the
2014 videos but that during the 2015 inspection, the lift either
did not malfunction at all or malfunctioned differently when
posed with the same tests. Based on the machine’s failing to
malfunction as it did in 2014 and at the time of the accident,
Boye assumed that the lift had been altered between 2014 and
2015. Because of the lift’s alleged alteration, Boye opined
that the “[parties] may never be able to find [out] what was
wrong originally.”
   Boye reported generally that the accident occurred from an
electrical malfunction. However, based on his overall observa-
tions, Boye was unable to precisely pinpoint what component
caused the lift to malfunction on the day of Pitts’ accident.
Although his report proposed an “overview of a few pos-
sibilities” that could have been the cause of the malfunction,
he conceded several times that he had no opinion as to what
specifically failed on August 21, 2013.
   The possible causes of the electrical malfunction were (1)
incorrect or shorted wiring; (2) bad components, such as bad or
touching diodes; (3) other bad or faulty components; (4) failed
or stuck limit switches; (5) the sticking of failed or “worn out”
switches, buttons, and relays; and (6) potential movement ear-
lier in the day of the accident which loosened diodes or wires
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          Nebraska Supreme Court A dvance Sheets
                  302 Nebraska R eports
                     PITTS v. GENIE INDUS.
                        Cite as 302 Neb. 88

and could have caused a short-circuit. He also thought the
taped button on the platform control panel may have been a
factor, but he was unsure how.
   Boye reported that Genie’s technical schematics and dia-
grams had at least 19 “errors and inconsistencies.” In other
words, in reviewing seven pages of the “Genie Service Manual”
and six sheets of the “ED, TZ34 DC Control” drawings, Boye
identified multiple inconsistencies between these documents as
to the lift’s design. However, he did not opine that the docu-
ments identified design defects. Boye stated that he was never
provided a number of documents that would have helped in the
evaluation, including certain design documents and other spec-
ifications and technical information regarding circuit elements.
He admitted in his deposition that these missing documents are
critical to understanding the design.
   Boye opined that the lift “could have been designed bet-
ter.” In particular, he suggested that Genie could have used
a “4-position keyed switch” instead of a “3-position keyed
switch.” As designed, the lift has a three-position switch in
which the user turns a key to activate either the platform con-
trol panel or the ground control panel or turns off the machine.
It is designed so that only one control panel can be activated
at a given time, and none of the buttons on the platform con-
trols should operate the outriggers. Still, Boye explained that
this technology could fail if diodes fail. In other words, power
could be sent to the outriggers even if the switch was in “plat-
form” position, if diodes failed.
   Considering the current design, Boye proposed a four-­
position switch as an alternative design which would have
“totally isolate[ed] the outrigger power from the platform
control panel.” He testified as to his design in a deposition
and stated that the three-position switch increased the risk of
a particular kind of electrical diode failure. But Boye admitted
that this four-position switch design could also fail. He also
admitted that this proposed four-position switch design would
require a completely revamped circuitry “from scratch.” Boye’s
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                Nebraska Supreme Court A dvance Sheets
                        302 Nebraska R eports
                             PITTS v. GENIE INDUS.
                                Cite as 302 Neb. 88

opinion was not peer reviewed, nor did Boye test or analyze
the feasibility of a four-position switch design.
   In 2017, Boye wrote and signed an additional affidavit for
the purposes of clarifying his testimony. This affidavit stated
that the lift tipped over because of an “electrical malfunction
in the lift’s circuit[r]y.” In the same affidavit, he again opined
that he could not determine the exact cause of the accident,
but that the lift was in an unreasonably dangerous condition
when it left Genie’s possession, because the platform and
ground control circuitry were interconnected, the diodes and
wires were too close together, the diodes and wires did not
have protective sheathing, and a three-position switch design
was used as opposed to a proposed four-position switch.
Boye did not elaborate as to the foundation of his conclu-
sion that these defects were present at the time it left Genie’s
possession and did not retract his prior testimony that six or
more possible causes could have resulted in the lift’s electri-
cal malfunction.

                 MotionsExclude Expert Testimony
                           to
                        Summary Judgment
                          and
   Genie moved to exclude Boye’s testimony and for sum-
mary judgment. The district court granted Genie’s motion
to exclude testimony in part and denied it in part. The court
held that Boye’s opinions regarding alternative design were
not admissible as they were not relevant and lacked reliability
under a Daubert/Schafersman1 analysis. However, the district
court overruled Genie’s motion to exclude testimony regard-
ing Boye’s opinions that the lift was unreasonably danger-
ous because the platform control and ground control circuitry
were “‘interconnected,’” the diodes and wires were too close
together, and the diodes and wires lacked adequate sheathing.

 1	
      See Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579, 113 S.
      Ct. 2786, 125 L. Ed. 2d 469 (1993), and Schafersman v. Agland Coop, 262
      Neb. 215, 631 N.W.2d 862 (2001).
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               Nebraska Supreme Court A dvance Sheets
                       302 Nebraska R eports
                            PITTS v. GENIE INDUS.
                               Cite as 302 Neb. 88

    The court then granted Genie’s motion for summary judg-
ment. The court held that the Pittses lacked the necessary
expert testimony for the proximate cause element of their
negligence and product liability claims. Boye’s expert testi-
mony, the court explained, only speculated a “‘choice of pos-
sibilities’” as to causation, and such testimony did not create
a fact question on summary judgment. The court held that the
malfunction theory could not be used to create a material issue
for proximate cause in this case because Boye pointed to sev-
eral specific defects. With no expert evidence to show that the
lift was defective at the time it left Genie’s possession or that
the defects proximately caused the platform controls to operate
the outriggers, the district court granted summary judgment in
favor of Genie on all claims.

                  ASSIGNMENTS OF ERROR
   The Pittses assign, reordered and rephrased, that the district
court erred in (1) finding that Genie was entitled to summary
judgment on the Pittses’ strict liability design defect claim,
(2) excluding portions of Boye’s expert testimony, (3) mis-
construing the scope of Boye’s opinion regarding causation,
(4) failing to consider and/or excluding evidence related to
issues of causation regarding the strict liability design defect
claim, (5) finding that Genie was entitled to summary judg-
ment with respect to the Pittses’ strict liability manufacturing
defect claim, and (6) failing to allow the Pittses to proceed on
and further apply the “malfunction theory” with regard to their
strict liability manufacturing defect claim.

                  STANDARD OF REVIEW
  [1] An appellate court reviews the district court’s grant of
summary judgment de novo, viewing the record in the light
most favorable to the nonmoving party and drawing all reason-
able inferences in that party’s favor.2

 2	
      Waldron v. Roark, 298 Neb. 26, 902 N.W.2d 204 (2017).
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                Nebraska Supreme Court A dvance Sheets
                        302 Nebraska R eports
                            PITTS v. GENIE INDUS.
                               Cite as 302 Neb. 88

   [2,3] We review de novo whether the trial court applied the
correct legal standards for admitting an expert’s testimony.3
But a trial court’s ruling in receiving or excluding an expert’s
testimony which is otherwise relevant will be reversed only
when there has been an abuse of discretion.4 A judicial abuse
of discretion exists when a judge, within the effective limits of
authorized judicial power, elects to act or refrain from acting,
but the selected option results in a decision which is unten-
able and unfairly deprives a litigant of a substantial right or a
just result in matters submitted for disposition through a judi-
cial system.5
                           ANALYSIS
   The Pittses contend that the district court erred in grant-
ing Genie’s motion for summary judgment against their strict
products liability design and manufacturing defects claims. The
Pittses argue that they presented sufficient evidence that the lift
was defectively designed, unreasonably dangerous, and defec-
tively manufactured at the time the lift left Genie’s posses-
sion to create a genuine dispute rendering summary judgment
improper. They add that they presented sufficient evidence of
causation as it relates to Pitts’ injuries.
   [4] In reviewing a summary judgment, an appellate court
views the evidence in the light most favorable to the party
against whom the judgment was granted, and gives that party
the benefit of all reasonable inferences deducible from the
evidence.6 An appellate court will affirm a lower court’s grant
of summary judgment if the pleadings and admitted evidence
show that there is no genuine issue as to any material facts or
as to the ultimate inferences that may be drawn from those

 3	
      King v. Burlington Northern Santa Fe Ry. Co., 277 Neb. 203, 762 N.W.2d
      24 (2009).
 4	
      Schafersman v. Agland Coop, supra note 1.
 5	
      Id.
 6	
      Green v. Box Butte General Hosp., 284 Neb. 243, 818 N.W.2d 589 (2012).
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                Nebraska Supreme Court A dvance Sheets
                        302 Nebraska R eports
                             PITTS v. GENIE INDUS.
                                Cite as 302 Neb. 88

facts and that the moving party is entitled to judgment as a
matter of law.7 In the summary judgment context, a fact is
material only if it would affect the outcome of the case.8
   [5,6] In a products liability cause of action based on strict
liability in tort, the central question involves the quality of the
manufactured product, that is, whether the product was unrea-
sonably dangerous.9 “Unreasonably dangerous” means that the
product has a propensity for causing physical harm beyond
that which could be contemplated by the ordinary user or con-
sumer.10 Whether the product is in a defective condition and
is unreasonably dangerous to its user are generally questions
of fact.11
   [7] In a products liability action based on defect, a plaintiff
must prove by a preponderance of the evidence that (1) the
defendant placed the product on the market for use and knew,
or in the exercise of reasonable care should have known, that
the product would be used without inspection for defects; (2)
the product was in a defective condition when it was placed on
the market and left the defendant’s possession; (3) the defect
is the proximate or a proximately contributing cause of the
plaintiff’s injury sustained while the product was being used in
a way and for the general purpose for which it was designed
and intended; (4) the defect, if existent, rendered the product
unreasonably dangerous and unsafe for its intended use; and
(5) the plaintiff’s damages were a direct and proximate result
of the alleged defect.12

 7	
      Freeman v. Hoffman-La Roche, Inc., 300 Neb. 47, 911 N.W.2d 591 (2018).
 8	
      See id.
 9	
      See, Stahlecker v. Ford Motor Co., 266 Neb. 601, 667 N.W.2d 244 (2003);
      Freeman v. Hoffman-La Roche, Inc., 260 Neb. 552, 618 N.W.2d 827
      (2000); Rahmig v. Mosley Machinery Co., 226 Neb. 423, 412 N.W.2d 56
      (1987).
10	
      Hancock v. Paccar, Inc., 204 Neb. 468, 283 N.W.2d 25 (1979).
11	
      Rahmig v. Mosley Machinery Co., supra note 9.
12	
      See Jay v. Moog Automotive, 264 Neb. 875, 652 N.W.2d 872 (2002).
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                Nebraska Supreme Court A dvance Sheets
                        302 Nebraska R eports
                            PITTS v. GENIE INDUS.
                               Cite as 302 Neb. 88

   [8] Proximate cause is the cause that in a natural and con-
tinuous sequence unbroken by an efficient intervening cause,
produces the injury, and without which the injury would not
have occurred.13 To establish proximate cause in a products lia-
bility action, the plaintiff must meet three basic requirements:
(1) Without the defect, the injury would not have occurred,
commonly known as the “but for” rule or “cause in fact”; (2)
the injury was a natural and probable result of the defect; and
(3) there was no efficient intervening cause.14
   [9,10] Findings of fact as to technical matters beyond the
scope of ordinary experience are not warranted in the absence
of expert testimony supporting such findings.15 With respect
to the requirement of expert testimony, the test is whether the
particular issue can be determined from the evidence presented
and the common knowledge and usual experience of the fact
finders.16 This case involves the mechanical functioning of
an aerial lift, its component parts, and its electrical circuitry,
which are technical matters well outside the scope of ordinary
experience. Therefore, to create a material issue of fact, the
Pittses were required to present expert testimony that a defec-
tive product caused the malfunction that led to Pitts’ injuries.
Their only expert was Boye. Thus, the question is whether
Boye’s testimony created issues of fact as to each element of
their products liability claims.17
   The notion of a defective product embraces two separate
concepts—a manufacturing defect and a design defect.18 A
manufacturing defect is one in which the product differs from

13	
      Hughes v. School Dist. of Aurora, 290 Neb. 47, 858 N.W.2d 590 (2015).
14	
      See, generally, Roskop Dairy v. GEA Farm Tech., 292 Neb. 148, 871
      N.W.2d 776 (2015).
15	
      Id.
16	
      McVaney v. Baird, Holm, McEachen, 237 Neb. 451, 466 N.W.2d 499 (1991).
17	
      See, Freeman v. Hoffman-La Roche, Inc., supra note 7; Roskop Dairy v.
      GEA Farm Tech., supra note 14.
18	
      See Freeman v. Hoffman-La Roche, Inc., supra note 9.
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               Nebraska Supreme Court A dvance Sheets
                       302 Nebraska R eports
                            PITTS v. GENIE INDUS.
                               Cite as 302 Neb. 88

the specifications and plan of the manufacturer, while a design
defect is one in which the product meets the specifications of
the manufacturer, but nonetheless poses an unreasonable risk
of danger.19 We first address the Pittses’ assignments of error
related to a design defect.
                          Design Defect
   The Pittses argue that they presented sufficient evidence to
show that defectively designed circuitry was the proximate
cause of the electrical malfunction that ultimately caused
Pitts’ injuries. They argue that the district court, in conclud-
ing that Boye’s testimony was speculative and inadequate to
create a material issue of fact as to causation, misunderstood
and mischaracterized Boye’s expert testimony. According to
the Pittses, Boye testified with sufficient certainty that the
electrical malfunction was caused by one of several possible
reasons, all of which could be attributed to design defects that
created an unreasonable danger of an electrical malfunction.
We disagree.
   [11] An expert must have “good grounds” for his or her
belief in every step of the analysis.20 The term “good grounds”
means an inference or assertion derived by scientific method
and supported by appropriate validation.21 Good grounds do
not include conclusions based on guess, speculation, con-
jecture, or a choice of possibilities.22 Conclusions based on
guess, speculation, conjecture, or a choice of possibilities do
not create material issues of fact for purposes of summary
judgment.23
   Boye initially presented an “overview of a few possibili-
ties” that could have been the cause of the malfunction, none

19	
      See id.
20	
      Roskop Dairy v. GEA Farm Tech., supra note 14.
21	
      Id.
22	
      See id.
23	
      Marksmeier v. McGregor Corp., 272 Neb. 401, 722 N.W.2d 65 (2006).
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                       PITTS v. GENIE INDUS.
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of which he directly identified as specifically relating to the
product’s design. Indeed, several possible causes appear to be
things that would have occurred after the lift left Genie’s pos-
session. The possible causes of the electrical malfunction were:
(1) incorrect or shorted wiring; (2) bad components, such as
bad or touching diodes; (3) other bad or faulty components; (4)
failed or stuck limit switches; (5) the sticking of failed or “worn
out” switches, buttons, and relays; and (6) potential movement
earlier on the day of the accident which loosened diodes or
wires and could have caused a short circuit. He also thought
the taped button on the platform control panel may have been
a factor, but he was unsure how. He asserted that Genie’s
three-position switch design could have been the cause of the
malfunction and provided, albeit untested and not reviewed by
peers, a four-position switch design as an alternative.
   Boye later attempted to clarify his opinion in a supplemen-
tal affidavit that was admitted into evidence by the district
court. In the affidavit, he opined that the lift was unreason-
ably dangerous when it left Genie’s possession because (1) the
platform and ground control circuitry were interconnected, (2)
the diodes and wires were too close together, (3) the diodes
and wires did not have proper protective sheathing, and (4)
Genie utilized a three-position switch design as opposed to a
proposed four-position switch. In the affidavit, Boye did not
retract his prior testimony that he had no opinion as to what
specifically failed and caused the accident on August 21, 2013.
In making its decision, the district court considered only the
first three elements of Boye’s opinion from the affidavit; it
excluded the alternate design of a four-position switch.
   [12,13] First, we find that the district court did not abuse
its discretion in determining that Boye was not qualified to
opine that the specific underlying design defect was the failure
to design the lift with a four-position switch. When a court
is faced with a decision regarding the admissibility of expert
opinion evidence, the trial judge must determine at the out-
set, pursuant to the evidence rule governing expert witness
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                             PITTS v. GENIE INDUS.
                                Cite as 302 Neb. 88

testimony, whether the expert is proposing to testify to (1)
scientific, technical, or other specialized knowledge that (2)
will assist the trier of fact to understand or determine a fact
in issue.24 This entails a preliminary assessment whether the
reasoning or methodology underlying the testimony is valid
and whether that reasoning or methodology properly can be
applied to the facts in issue.25 In evaluating expert opinion
testimony under Daubert/Schafersman, where such testimony’s
factual basis, data, principles, methods, or their application are
called sufficiently into question, the trial judge must determine
whether the testimony has a reliable basis in the knowledge
and experience of the relevant discipline.26
   It is undisputed that Boye had expertise in the field of
electrical engineering, but Boye testified that he did not know
how any other aerial lifts are designed and admitted he was
unaware of the standards used in the industry for the design
and manufacture of machines of this nature. He provided no
evidence of any other lift manufacturer’s utilizing a four-
position switch design. He stated that his four-position switch
design was conceptual. He did not actually create and test his
theory, nor was his assertion peer reviewed by other electrical
engineers. He further asserted that, even with a four-position
switch instead of Genie’s three-position switch, an electrical
malfunction could still have occurred. Without testing, peer
review, and knowledge of whether this theory or alternative
design would be generally accepted in the industry, Boye’s
expert opinion that the lift should have been designed with a
four-position switch was simply unreliable under a Daubert/
Schafersman analysis. As such, the district court did not abuse
its discretion in determining that Boye lacked knowledge in
the relevant discipline to testify that the lift should have been

24	
      Schafersman v. Agland Coop, supra note 1. See, also, Neb. Evid. R. 702,
      Neb. Rev. Stat. § 27-702 (Reissue 2016).
25	
      Schafersman v. Agland Coop, supra note 1.
26	
      Id.
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                          Cite as 302 Neb. 88

designed with a four-position switch and in excluding those
portions of his testimony.
   As to the remainder of Boye’s testimony that was admit-
ted into evidence, we find that the district court did not err in
granting summary judgment in favor of the Pittses. Boye, as
a qualified and trained electrical engineer, reviewed pictures,
diagrams, and charts related to the wiring and schematics of
the machine. Boye generally opined that the lift was unreason-
ably dangerous in its design because it had inadequate sheath-
ing, interconnected circuitry, and that diodes that were too
close in proximity. Essentially, his affidavit testimony asserts
that these unreasonably dangerous conditions are defects in
Genie’s design. However, Boye testified that any one of a
number of problems or occurrences, including those not linked
to design and outside of Genie’s control after the point of sale,
could have been the actual cause of the electrical malfunction
that resulted in Pitts’ injuries.
   Specifically, Boye stated that one of six or more possibili-
ties could have been the cause of the accident. While some of
the initial report’s “possibilities” could possibly be connected
to the affidavit’s “unreasonably dangerous” elements of the
design, others cannot. For example, Boye stated that a failed
limit switch, faulty components or diodes, or even recalled
parts could have been the cause of the malfunction. He even
stated that incorrect, damaged, or shorted wiring could have
easily caused the malfunction, which he notes was altered or
repaired just months prior to Pitts’ accident. He also stated that
the taped leveling button could have been a cause of the acci-
dent. Boye was unable to precisely pinpoint what component
caused the lift to malfunction on the day of Pitts’ accident.
Although his report proposed an “overview of a few pos-
sibilities” that could have been the cause of the malfunction,
he conceded several times that he had no opinion as to what
specifically failed on August 21, 2013.
   Some courts have held that a particular product may be
sufficiently identified as having caused harm even though
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                             PITTS v. GENIE INDUS.
                                Cite as 302 Neb. 88

the evidence does not exclude every other possible cause.27
However, courts clarify that, though the plaintiff is not required
to eliminate all possible causes, the plaintiff must still establish
a logical sequence of cause and effect between the defect and
the injury.28 We need not decide in this case if the Pittses were
required to eliminate all possible nondesign causes in order to
create a material issue of fact, because even if they were not,
the evidence’s logical sequence of cause and effect was lack-
ing. In other words, Boye did not opine with a requisite degree
of certainty that any of the “possibilities” was the one that
caused the malfunction.
   [14] We have held that expert testimony “based upon pos-
sibility or speculation is insufficient [to establish causation];
it must be stated as being at least ‘probable,’ in other words,
more likely than not.”29 Even assuming that Boye’s reasons
for the lift’s being in an “unreasonably dangerous condition”
were all affirmatively connected to the lift’s design, he failed
to sufficiently connect the possible causes of the malfunc-
tion stated in his report to these design defects. Throughout
his opinion, Boye merely speculated that defects could have
been related to the ultimate cause of the malfunction, while
also proposing potential causes that overtly did not relate to
Genie’s design, such as the failure of a limit switch, the taped
over leveling button, or faulty components. Because of the
intermingling of possible causes that are related and unrelated
to the design, with no testimony that any one of them was
more probable than another, there is no way for a fact finder
to determine without speculation whether a defective design

27	
      See 49 Am. Jur. Proof of Facts 2d 293 Defect Not Cause § 3 (1987 &
      Supp. 2018).
28	
      See id. See, also, Whitmire v. Terex Telelect, Inc., 390 F. Supp. 2d 540
      (E.D. Tex. 2005); Skinner v Square D Co, 445 Mich. 153, 516 N.W.2d
      475 (1994); MASB-SEG v. Metalux, 231 Mich. App. 393, 586 N.W.2d 549
      (1998).
29	
      Fackler v. Genetzky, 263 Neb. 68, 74, 638 N.W.2d 521, 528 (2002).
      Accord Barrett v. Rhodia, Inc., 606 F.3d 975 (8th Cir. 2010).
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was the proximate cause of the electrical malfunction and
Pitts’ injuries.
   In sum, Boye’s testimony as to causation was too specula-
tive for a jury to conclude that the specific alleged design
defect or defects were the “but for” cause of the electrical
malfunction leading to Pitts’ injuries. Because failure of proof
concerning an essential element of the nonmoving party’s case
on a motion for summary judgment necessarily renders all
other facts immaterial,30 we hold that the district court did not
err in finding that there remained no genuine issue of fact as to
the element of causation and that Genie was entitled to judg-
ment as a matter of law on the Pittses’ strict liability design
defect claim.
                  M anufacturing Defect and
                      M alfunction Theory
   In addition to the Pittses’ design defect claim, they assert
that the district court erred in granting summary judgment
against their strict liability manufacturing defect claim. The
Pittses rely on what is known as the malfunction theory to
support the causation prong of this claim. They contend that
although they presented evidence of specific design defects,
they did not present any direct evidence that there was a spe-
cific manufacturing defect. They assert that in lieu of prov-
ing a specific manufacturing defect, the malfunction theory
allows them to circumstantially prove an unspecified defect
in the lift.
   [15,16] The malfunction theory is based on the same princi-
ple underlying res ipsa loquitur, which permits a fact finder to
infer negligence from the circumstances of the incident, with-
out resort to direct evidence of the wrongful act.31 Under the
malfunction theory, also sometimes called the indeterminate
defect theory or general defect theory,32 a plaintiff may prove

30	
      See Freeman v. Hoffman-La Roche, Inc., supra note 7.
31	
      Roskop Dairy v. GEA Farm Tech., supra note 14.
32	
      Id.
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                             PITTS v. GENIE INDUS.
                                Cite as 302 Neb. 88

a product defect circumstantially, without proof of a specific
defect, when (1) the incident causing the harm was of a kind
that would ordinarily occur only as a result of a product defect
and (2) the incident was not, in the particular case, solely the
result of causes other than a product defect existing at the time
of sale or distribution.33
   [17,18] The malfunction theory is narrow in scope. The
theory simply provides that it is not necessary for the plaintiff
to establish a specific defect so long as there is evidence of
some unspecified dangerous condition or malfunction from
which a defect can be inferred—the malfunction itself is cir-
cumstantial evidence of a defective condition.34 The malfunc-
tion theory does not alter the basic elements of the plaintiff’s
burden of proof and is not a means to prove proximate cause or
damages.35 Although some circumstances may justify the use
of the malfunction theory to bridge the gap caused by miss-
ing evidence, the absence of evidence does not make a fact
more probable but merely lightens the plaintiff’s evidentiary
burden despite the fact that the missing evidence might well
have gone either way, and this rationale is too often subject
to misapplication by courts in situations in which evidence is
actually available.36
   As a matter of policy, the malfunction theory is meant to
allow circumstantial proof of a product defect without evi-
dence of the specific defect, because in many instances, the
dealer or manufacturer has either purposefully or inadvertently
tampered with the evidence.37 When examination of the prod-
uct unit is impossible because the unit is lost or destroyed
after the harm-causing incident, responsibility for spoliation

33	
      Id. (citing Restatement (Third) of Torts: Products Liability § 3, comment
      a. (1998)).
34	
      Roskop Dairy v. GEA Farm Tech., supra note 14.
35	
      Id.
36	
      Id.
37	
      Id.
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                              PITTS v. GENIE INDUS.
                                 Cite as 302 Neb. 88

of evidence may be relevant to the application of the malfunc-
tion theory.38
   [19] We have yet to expressly hold that the malfunction
theory applies to strict liability claims,39 but we have made the
malfunction theory available to plaintiffs in an implied war-
ranty context.40 And we have approved of the general approach
set forth in the Restatement (Third) of Torts § 2(b)41 that identi-
fies a product defect as the core similarity between strict liabil-
ity and implied warranty claims, thereby merging theories of
recovery for implied warranty with theories of recovery based
on allegations of design or manufacturing defects.42 There is
no reason to prohibit the malfunction theory in a strict liability
matter when we do not do so for its implied warranty coun-
terpart. We hold that the malfunction theory is applicable in a
strict liability manufacturing defect claim.
   [20] To support a manufacturing defect through the malfunc-
tion theory, the Pittses rely on Boye’s opinion that, given the
nature of the malfunction that occurred, “the only reasonable
inference to be drawn from this set of events is that a flaw in
the lift’s circuitry caused this electrical malfunction.” However,
they simultaneously point to several specific design defects in
their design defect claim, as we discussed above. We recently
held in O’Brien v. Cessna Aircraft Co.43 that the malfunction
theory is not available when specific defects are alleged.
   In O’Brien, a commercial pilot specifically claimed that
the deicing system on the plane was defectively designed and

38	
      See Restatement, supra note 33, comment b.
39	
      See O’Brien v. Cessna Aircraft Co., 298 Neb. 109, 903 N.W.2d 432 (2017).
40	
      See, e.g., Genetti v. Caterpillar, Inc., 261 Neb. 98, 621 N.W.2d 529 (2001)
      (holding that precise or specific defect does not need to be proved in order
      to find product defective).
41	
      Restatement, supra note 33, § 2(b).
42	
      Freeman v. Hoffman-La Roche, Inc., supra note 9. See, also, Shuck v. CNH
      America, LLC, 498 F.3d 868 (8th Cir. 2007).
43	
      O’Brien v. Cessna Aircraft Co., supra note 39.
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unreasonably dangerous. He argued that it was defectively
designed, because the deicing boot provided insufficient cov-
erage and the deicing system lacked a water separator to pre-
vent contaminants from entering and affecting its operation.
The pilot then attempted to rely on the malfunction theory to
prove a nonspecific defect that the aircraft was susceptible to
“‘ice contaminated tail stall.’”44 We held that because the pilot
alleged that the plane crash was caused by several specific
design defects, he could not simultaneously rely on the mal-
function theory in an effort to prove the accident was caused
by a nonspecific defect rendering the aircraft susceptible to
“ice contaminated tail stall.”45
   This case mirrors O’Brien in that the Pittses have pointed
to evidence of specific design defects in the lift that possibly
caused an electrical malfunction; but, later, in an effort to
forward his manufacturing defect theory, relied on the mal-
function theory by generally asserting that a flaw in the lift’s
circuitry caused this electrical malfunction. For this reason, the
malfunction theory is inapplicable in this case and the district
court did not err in refusing to apply it. We need not address
whether there are additional reasons why the Pittses failed to
create a material issue of fact for recovery under the malfunc-
tion theory.
   There being no other evidence of a manufacturing defect,
the district court did not err in granting summary judgment
in favor of Genie on the Pittses’ strict liability manufacturing
defect claim.
                        CONCLUSION
   For the foregoing reasons, we affirm the district court’s
grant of summary judgment as to the Pittses’ strict products
liability defect claim.
                                                 A ffirmed.

44	
      Id. at 114, 903 N.W.2d at 443.
45	
      O’Brien v. Cessna Aircraft Co., supra note 39.
