                                                                         FILED
                     UNITED STATES COURT OF APPEALS          United States Court of Appeals
                                                                     Tenth Circuit
                            FOR THE TENTH CIRCUIT
                        _________________________________         February 25, 2016

ANTHONY TABER; MARKEETA                                          Elisabeth A. Shumaker
TABER,                                                               Clerk of Court

     Plaintiffs - Appellants,

v.                                                   No. 15-6113
                                              (D.C. No. 5:13-CV-00773-D)
ALLIED WASTE SYSTEMS, INC., d/b/a                  (W.D. Oklahoma)
Allied Waste Service of Oklahoma City,

     Defendant Third-Party
     Plaintiff - Appellee,

v.

MANSFIELD OIL COMPANY OF
GAINESVILLE, INC.,

     Third-Party Defendant.


ANTHONY TABER; MARKEETA
TABER,

     Plaintiffs,

v.                                                   No. 15-6120
                                              (D.C. No. 5:13-CV-00773-D)
ALLIED WASTE SYSTEMS, INC., d/b/a                  (W.D. Oklahoma)
Allied Waste Service of Oklahoma City,

     Defendant Third-Party
     Plaintiff - Appellant,

v.
MANSFIELD OIL COMPANY OF
GAINESVILLE, INC.,

      Third-Party Defendant - Appellee.
                       _________________________________

                            ORDER AND JUDGMENT*
                        _________________________________

Before GORSUCH, BACHARACH, and McHUGH, Circuit Judges.
                  _________________________________




                               I.   INTRODUCTION

      Anthony Taber was injured when he fell from a ladder while delivering fuel to

an Allied Waste Systems facility. Mr. Taber and his wife filed suit against Allied.

Because Mr. Taber has no memory of how he fell, the Tabers retained two experts to

opine as to the cause of his fall. Allied successfully moved to exclude the testimony

of the Tabers’ experts, resulting in summary judgment for Allied. The Tabers now

appeal.

      We conclude the district court acted within its discretion in excluding the

Tabers’ experts. Without that expert causation testimony, the Tabers could not

establish a necessary element of their claims. We therefore affirm the district court’s

decision granting summary judgment in favor of Allied.




      *
         This order and judgment is not binding precedent, except under the doctrines
of law of the case, res judicata, and collateral estoppel. It may be cited, however, for
its persuasive value consistent with Fed. R. App. P. 32.1 and 10th Cir. R. 32.1.
                                           2
                                 II.   BACKGROUND

                                A. Factual Background

       Mr. Taber, a fuel-truck driver, sustained serious injuries when he fell from a

ladder on a fuel tank at an Allied facility. When Mr. Taber arrived at Allied’s facility

on the day of the accident, he learned the gauge for the fuel tank was not working. He

therefore had to manually measure the fuel level in the tank—both before and after

filling it—by climbing a ladder to the top of the tank and using a fuel stick to take the

measurement. Mr. Taber climbed the ladder to the top of the tank, took a fuel

measurement, descended the ladder, and then loaded fuel from his truck into the tank.

Upon filling the tank, he climbed the ladder and again measured the fuel level. Mr.

Taber’s accident occurred when he “turned around and proceeded down the ladder.”

After “taking a couple or a few steps,” Mr. Taber fell, and the next thing he

remembers is “somebody hollering at [him]” as he lay on the ground. Mr. Taber was

found unconscious on the pavement below the ladder. He sustained a spinal cord

injury resulting in partial paralysis to his extremities.

                              B. Procedural Background

       Mr. Taber and his wife, Markeeta Taber, filed a premises-liability claim

against Allied in Oklahoma state court, alleging the fuel-tank ladder was a

“dangerous climbing structure that does not meet safety guidelines.” Allied removed

the action to federal court. Allied then filed a third-party complaint against Mansfield

Oil Company, seeking indemnification pursuant to a master services agreement under

which Mr. Taber delivered fuel to Allied on Mansfield’s behalf.

                                             3
        The Tabers retained two expert witnesses to opine that design defects in the

fuel-tank ladder caused Mr. Taber’s fall. Dr. Bob Block is a professional engineer

and metallurgist, who evaluated the ladder’s compliance with standards promulgated

by the American National Standards Institute (ANSI) and the Occupational Safety

and Health Administration (OSHA) relating to rung spacing and step placement.

Dr. Block opined that the ladder’s geometry—specifically the twenty-two-inch intra-

rung spacing and the placement of the top step below the level of the surface served

by the ladder—violated OSHA requirements and that these violations were “a direct

or contributing cause” of Mr. Taber’s accident.

        Dr. J.P. Purswell is a professional engineer specializing in human factors and

ergonomics. Dr. Purswell opined that “[t]he 22 inch spacing between the rungs make

it much more difficult and much less safe for a person to ascend or descend this

ladder than if the ladder had been constructed in compliance with OSHA and ANSI

requirements.” Dr. Purswell observed that the twenty-two-inch intra-rung spacing

was “very far outside the range typically considered suitable for a fixed ladder.”

Dr. Purswell also noted that the rungs were tilted at various angles away from the

fuel tank, and opined that these angled rungs “reduced the available slip resistance . .

. and increased the likelihood that a person’s foot would slip off the rung and the

person would fall.” Mr. Purswell therefore opined that it is more likely than not that

both the intra-rung spacing and the angled rungs caused or contributed to Mr. Taber’s

fall.



                                            4
      Allied filed a motion to exclude the opinions of Dr. Block and Dr. Purswell

under Daubert v. Merrell Dow Pharmaceuticals, 509 U.S. 579 (1993). Allied also

filed a motion for summary judgment, arguing that without the expert opinions of

Dr. Block and Dr. Purswell, the Tabers had no evidence to show a defect in the

ladder was the cause of Mr. Taber’s injuries.

      In its Daubert motion, Allied argued Dr. Block and Dr. Purswell lacked

expertise in the relevant field of ladder design and construction, that their opinions

were unsupported by the facts of the case, that the experts failed to perform any

testing of their conclusions or rule out alternative causes for Mr. Taber’s fall, and that

the experts’ opinions constituted impermissible legal conclusions. The district court

granted Allied’s motion, ruling Dr. Block was not qualified to give an opinion due to

a lack of relevant expertise in ladder design or accident reconstruction. The district

court also ruled Dr. Block’s opinion was unreliable, in that it was based on

unsupported speculation and did not “set forth any underlying methodology, any

statistical analysis related to ladder injuries, or any other supporting data.” The court

specifically noted Dr. Block’s failure to test his theory of causation by reconstructing

the accident and his failure to rule out other potential causes identified by the

defendant.

      With respect to Dr. Purswell, the district court found his expertise in

ergonomics and experience with OSHA regulation and ANSI standards qualified him

to opine on causation. But the district court concluded Dr. Purswell’s testimony was

unreliable. The district court observed that, like Dr. Block, Dr. Purswell had not

                                            5
attempted to test his theory by reconstructing the accident or “perfom[ing] any type

of experimentation.” Nor had Dr. Purswell accounted for other factors that may have

caused or contributed to Mr. Taber’s fall. The district court therefore concluded Dr.

Purswell’s opinion was not based on “any reliable methodology” and should be

excluded.

      Finally, the district court ruled that neither expert’s testimony would be

helpful to the jury insofar as it entailed explaining that the ladder’s rung spacing

failed to comply with OSHA or ANSI standards, which straightforwardly required a

rung spacing of twelve inches. Because the ladder in question undisputedly had a

rung spacing greater than twelve inches, the district court found that expert testimony

merely opining the ladder violated relevant standards would not assist the jury.

      Having excluded the Tabers’ experts, the district court granted Allied’s motion

for summary judgment. The district court observed that Mr. Taber did not know how

he fell and that the Tabers had not introduced any other evidence to prove causation.

Without expert testimony as to causation, the district court concluded the Tabers

could not establish the requisite elements of their negligence claim and Allied was

therefore entitled to judgment as a matter of law. Mansfield also filed a motion for

summary judgment on Allied’s claim for indemnification, which the district court

granted.

      The Tabers filed a timely motion to alter or amend the judgment under Rule

59(e). In that motion, the Tabers “apologize[d] to the Court for not fully developing

the facts and circumstances surrounding the causation issue in its Response to

                                            6
Defendant’s Motion for Summary Judgment.” The Tabers further contended that the

“failure to properly set forth the facts of the day in question has led to a manifest

injustice.” The Tabers then directed the district court to testimony from Mr. Taber’s

deposition that had not been set forth in the Tabers’ opposition to summary

judgment, but which they claimed provided direct evidence that the extended rung

spacing caused Mr. Taber’s fall. The Tabers also sought to introduce new evidence:

an affidavit from Dr. Block—in substance a supplemental expert report—attempting

to remedy the deficiencies observed by the district court in reviewing Dr. Block’s

qualifications and analysis.

       The district court denied the Tabers’ motion to alter or amend the judgment,

reasoning the Tabers had provided no explanation why this evidence could not have

been submitted as part of the summary judgment or Daubert briefing. The district

court also stated that nothing in Dr. Block’s affidavit undermined the factual or legal

bases of the district court’s decision to exclude his testimony. In conclusion, the

district court ruled the Tabers’ “failure to present their strongest case in the first

instance does not entitle them to a second chance in the form of a motion to

reconsider.” The Tabers now appeal.1



       1
         Allied also conditionally appealed the summary judgment in favor of
Mansfield on Allied’s indemnification claim, in the event this court reversed the
district court’s grant of summary judgment to Allied on the Tabers’ claims. Because
we affirm the district court’s grant of summary judgment to Allied, “there is no basis
to hear [an appeal] that is conditioned on reversal of that judgment.” Weaver v.
Blake, 454 F.3d 1087, 1101 (10th Cir. 2006). Accordingly, we dismiss Allied’s
conditional appeal as moot. Id.
                                             7
                                    III. ANALYSIS

       The Tabers raise two challenges to the district court’s rulings. First, they argue

the district court abused its discretion in excluding the testimony of their experts, Dr.

Block and Dr. Purswell. Second, the Tabers argue Mr. Taber’s deposition testimony

is sufficient by itself to preclude the grant of summary judgment to Allied. Although

the Tabers do not challenge the district court’s decision denying relief under Rule

59(e), they rely in large part on the evidence presented to the district court in their

postjudgment Rule 59(e) motion. We therefore begin our analysis by clarifying the

scope of our review. We then proceed to the merits, considering first the Tabers’

challenge to the exclusion of their experts and, second, their challenge to the entry of

summary judgment for Allied.

       “As a reviewing court, we may only ‘evaluate the trial court’s decision from

its perspective when it had to rule and not indulge in review by hindsight.’” Hertz v.

Luzenac Am., Inc., 370 F.3d 1014, 1019 (10th Cir. 2004) (quoting Old Chief v.

United States, 519 U.S. 172, 182 n.6 (1997)). Thus, our review is generally limited

“to the record that was before the district court when it made its decision.” Regan-

Touhy v. Walgreen Co., 526 F.3d 641, 648 (10th Cir. 2008). And in reviewing a

summary-judgment ruling, we further limit our review to “the materials adequately

brought to the attention of the district court by the parties.” Adler v. Wal-Mart Stores,

Inc., 144 F.3d 664, 671 (10th Cir. 1998).

       Here, the Tabers do not challenge the district court’s denial of their Rule 59(e)

motion. Instead, they appeal the district court’s rulings excluding their expert

                                            8
witnesses and granting summary judgment to Allied. Our review is thus limited to the

evidence in the record before the district court and adequately brought to its attention

at the time it rendered the challenged decisions. Regan-Touhy, 526 F.3d at 648;

Adler, 144 F.3d at 671. That means we will not consider evidence introduced into the

record or brought to the district court’s attention for the first time in the Tabers’ Rule

59 motion. See Bryson v. City of Oklahoma City, 627 F.3d 784, 788 (10th Cir. 2010)

(explaining that where the denial of a postjudgment “motion to reconsider” is not

shown to be an abuse of discretion, this court “will not consider any of the new

evidence presented for the first time in [the] motion to reconsider”).

                    A. Exclusion of the Tabers’ Expert Witnesses

      Turning to the merits, we first consider the Tabers’ challenge to the exclusion

of their expert witnesses. The admissibility of expert testimony is governed by Rule

702 of the Federal Rules of Evidence and the framework set forth in Daubert v.

Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993). In reviewing the exclusion

of expert testimony, we review de novo whether the district court performed its

Daubert “gatekeeping” function, but we review for an abuse of discretion the manner

in which the district performed that function. Bitler v. A.O. Smith Corp., 400 F.3d

1227, 1232 (10th Cir. 2004). To permit this court to adequately review the district

court’s conclusions, the district court must make sufficiently specific factual findings

with respect to the reliability and relevancy of the expert testimony. Id. But so long

as the district court performs its obligations under Rule 702 and Daubert, we will not

disturb its decision to exclude expert testimony absent a conclusion that the decision

                                            9
is “arbitrary, capricious, whimsical, manifestly unreasonable, or clearly erroneous.”

Id.

       Here, the Tabers do not argue the district court failed to perform its

gatekeeping role or to support its conclusions with adequate findings. Accordingly,

our review is confined to whether the district court abused its “wide latitude” of

discretion in excluding the Tabers’ experts. Id. In performing a Daubert analysis,

“the district court generally must first determine whether the expert is qualified ‘by

knowledge, skill, experience, training, or education’ to render an opinion.” United

States v. Nacchio, 555 F.3d 1234, 1241 (10th Cir. 2009) (quoting Fed. R. Evid. 702).

If the expert is sufficiently qualified, the district court must then consider whether the

expert’s opinion is both relevant and reliable. Daubert, 509 U.S. at 589.

1. Dr. Block

       The district court excluded Dr. Block’s testimony, concluding that he was

unqualified to opine on the cause of Mr. Taber’s fall, that his opinion was unreliable,

and that his testimony would not be relevant to the jury. Because we conclude the

district court did not exceed its discretion by finding Dr. Block unqualified, we

affirm the district court’s ruling on that basis and do not reach the other grounds for

its decision.

       “District courts have broad discretion in determining the competency of

expert witnesses.” United States v. Nichols, 169 F.3d 1255, 1265 (10th. Cir. 1999).To

qualify as an expert, a proposed witness must possess “such skill, experience or

knowledge in that particular field as to make it appear that his opinion would rest on

                                           10
substantial foundation and would tend to aid the trier of fact in his search for truth.”

LifeWise Master Funding v. Telebank, 374 F.3d 917, 928 (10th Cir. 2004) (quoting

Graham v. Wyeth Labs, 906 F.2d 1399, 1408 (10th Cir. 1990)). An expert who

“possesses knowledge as to a general field” but “lacks specific knowledge does not

necessarily assist the jury.” City of Hobbs v. Hartford Fire Ins. Co., 162 F.3d 576,

587 (10th Cir. 1998). Proposed expert testimony must therefore “fall within the

reasonable confines of [the witness’s] expertise.” Conroy v. Vilsack, 707 F.3d 1163,

1169 (10th Cir. 2013) (internal quotation marks omitted). The proponent of expert

testimony bears the burden of demonstrating the expert’s qualification. Ralston v.

Smith & Nephew Richards, Inc., 275 F.3d 965, 970 n.4 (10th Cir. 2001).

      On appeal, the Tabers do not expressly challenge the district court’s ruling on

Dr. Block’s qualifications. While their statement of the case sets forth facts regarding

Dr. Block’s qualifications, the Tabers do not explain how these facts demonstrate the

district court abused its discretion in finding Dr. Block unqualified. But even if we

conclude the Tabers adequately raised this issue on appeal, they nevertheless have

failed to demonstrate the district court abused its discretion.

      In ruling that Dr. Block was not qualified to testify as an expert regarding the

cause of Mr. Taber’s fall, the district court made a number of findings. The district

court observed that while Dr. Block had conducted an estimated one thousand

“investigations and evaluations of injury-producing accidents,” Dr. Block could

recall working on only one case involving a fixed ladder “some years ago” and could

not recall the details of the accident. The district court also noted that Dr. Block

                                           11
“does not have any experience in ladder design or manufacture, has never served on

ANSI committees regarding standards applicable to ladders and has never published

any articles about ladder design.” And the district court found the record contained

“no evidence of [Dr.] Block’s experience in the field of accident reconstruction.”

These findings were based on Dr. Block’s experience as related in his expert report

and deposition testimony, which is all that had then been presented to the district

court. Based on those findings, the district court concluded Dr. Block lacked specific

knowledge and expertise in the area of ladder design and ladder-accident

investigation.

      The Tabers do not challenge the district court’s focus on fixed-ladder accidents

as the relevant area of expertise. And our review indicates that district courts

routinely consider experts’ specific experience with ladder design and accident

investigation when evaluating their qualifications in ladder-accident cases. See, e.g.,

Rupolo v. Oshkosh Truck Corp., 749 F. Supp. 2d 31, 39 (E.D.N.Y. 2010) (finding

expert qualified to testify to causation in ladder-accident case where expert was

voting member of ANSI Ladder Safety Committee, had published three peer-

reviewed technical papers on ladder safety, and had investigated over 100 accidents

involving falls from ladders); Delehanty v. KLI, Inc., 663 F. Supp. 2d 127, 132

(E.D.N.Y. 2009) (finding expert unqualified to testify to causation in ladder-accident

case where expert had “no expertise in either ladder design or ladder accident

reconstruction,” had never designed or tested a ladder, and had never conducted

studies or authored articles “specific to ladder design or accidents”); Sittig v.

                                            12
Louisville Ladder Grp. LLC, 136 F. Supp. 2d 610, 616 (W.D. La. 2001) (finding two

experts unqualified to testify regarding ladder defects because neither expert was

qualified in the “relevant field” of ladder design).

       Instead, the Tabers attempt to bolster Dr. Block’s qualifications with an

affidavit from Dr. Block submitted with the Tabers’ Rule 59(e) motion. There, the

Tabers set forth for the first time that Dr. Block had investigated accidents involving

fixed ladders on at least two previous occasions, that he had investigated two dozen

or more accidents involving portable metal ladders, and that he had worked as a

consultant for several months for a ladder manufacturer. But this evidence was not

before the district court when it ruled on the motion to exclude Dr. Block and, for the

reasons stated above, the evidence is outside the scope of our review. See Regan-

Touhy, 526 F.3d at 648. Thus, the Tabers have failed to demonstrate the district court

abused its discretion in concluding Dr. Block was unqualified to testify as to the

cause of Mr. Taber’s fall, and we affirm the exclusion of Dr. Block’s testimony on

that basis.

2. Dr. Purswell

       Although the district court concluded Dr. Purswell was qualified to testify on

the issue of causation, it determined Dr. Purswell’s testimony was unreliable. Rule

702 permits the admission of expert testimony that is “based on sufficient facts or

data” and is “the product of reliable principles and methods” that have been “reliably

applied” to the facts of the case. Fed. R. Evid. 702. To determine if this reliability

standard has been satisfied, the district court must consider “whether the reasoning or

                                           13
methodology underlying the testimony is scientifically valid.” Daubert, 509 U.S. at

592–93. This inquiry requires the district court to focus on the methodology

employed by the expert rather than the precise conclusions reached. Id. at 595. But

where “the conclusion simply does not follow from the data, a district court is free to

determine that an impermissible analytical gap exists between premises and

conclusion.” Bitler, 400 F.3d at 1233. “Because the district court has discretion to

consider a variety of factors [in] assessing reliability under Daubert, and because, in

light of that discretion, there is not an extensive body of appellate case law defining

the criteria for assessing scientific reliability, we are limited to determining whether

the district court’s application of the Daubert [standard] manifests a clear error of

judgment or exceeds the bounds of permissible choice in the circumstances.”

Hollander v. Sandoz Pharm. Corp., 289 F.3d 1193, 1206 (10th Cir. 2002).

      Dr. Purswell’s theory of Mr. Taber’s fall is based on his expertise in

ergonomics and biomechanics. Dr. Purswell is an engineer and ergonomics

professional and has written and presented on topics including OSHA compliance

and ergonomics hazards. In preparing his opinion, Dr. Purswell also reviewed the

literature related to the biomechanics of ascending and descending a ladder.

Dr. Purswell provided the biomechanical analysis underlying his opinion at his

deposition. According to Dr. Purswell, the ladder’s large intra-rung spacing would

make it difficult to maintain three-point contact with the ladder—either two hands

and one foot or two feet and one hand—while descending, and the angled rungs

exacerbated the risk of falling “because you’re leaning backward, away from the

                                           14
ladder as you’re trying to get your foot in a position where you get down to the next

step and still have your body and your torso on the step that you’re in contact with.”

Dr. Purswell explained that this configuration “puts your center of gravity far away

from your base of support. And combined with the angled rungs, that makes it more

likely that foot or hands will slip.”

       Applying these principles here, Dr. Purswell concluded that, because

Mr. Taber was “a shorter fellow,” when descending the ladder “he had to hang on to

his hands and had to pull up his one knee into his chest and try to reach his leg . . .

from the next lower rung. And as he was doing that, the combined angle of tilt on the

rung he was on, combined with the way he had to have his center of gravity so far

over his base of support or it’d reach down to the next level, caused him to fall.”

Based on this analysis, Dr. Purswell opined “it is more likely than not” that both the

large intra-rung spacing and the angled rungs of the ladder caused or contributed to

Mr. Taber’s fall.

       The district court concluded Dr. Purswell’s testimony was unreliable because

Dr. Purswell had not tested his theory by reconstructing the accident and had not

adequately considered and excluded other causes. The Tabers argue the district court

abused its discretion in reaching this conclusion because Dr. Purswell was not

required to test his theory and he adequately considered other alternative

explanations.




                                            15
      a. Failure to Test

      The Tabers argue, based on our decision in Bitler v. A.O. Smith Corp., 400

F.3d 1227 (10th. Cir 2004), that “testing is not required in all expert opinion

testimonies” and that “[Dr.] Purswell’s testimony relies upon accepted standards and

practices,” which need not be tested. But the Tabers failed to raise this argument to

the district court in opposing Allied’s motion to exclude Dr. Purswell. Although

Allied argued below that “where an expert fails to test his conclusions, his opinions

are not reliable and should be excluded,” the Tabers failed to respond to this

argument in their opposition to Allied’s motion. Again, the Tabers first raised this

argument when they sought reconsideration of the district court’s ruling under Rule

59. “We have held that a party’s attempt to raise a new argument in a motion for

reconsideration is not sufficient to preserve it for appeal.” Martin Marietta Materials,

Inc. v. Kansas Dep't of Transp., 810 F.3d 1161, 1173 (10th Cir. 2016) (internal

quotation marks omitted). Because the Tabers failed to raise this argument to the

district court until their motion for reconsideration, it is unpreserved for our review

on appeal.

      But even if we consider the Tabers’ argument on its merits, they have not

demonstrated the district court abused its discretion in concluding Dr. Purswell’s

failure to test his theory negatively impacted its reliability. To establish an expert’s

testimony as reliable, the proponent is not required to show the expert’s methodology

is generally accepted or indisputably correct; he need show only that it is

scientifically sound. Bitler, 400 F.3d at 1233. The Supreme Court has identified

                                            16
factors that may bear on the district court’s evaluation of the reliability of an expert’s

methodology: “(1) whether a theory has been or can be tested or falsified, (2)

whether the theory or technique has been subject to peer review and publication, (3)

whether there are known or potential rates of error with regard to specific techniques,

and (4) whether the theory or approach has ‘general acceptance.’” Id. And this court

has recognized that these factors are “most relevant in the context of a new and novel

scientific theory.” Id. Where the reliability of the underlying science is not in dispute,

“the need for testing is not at its highest.” Id. at 1236.

       In Bitler, the plaintiffs’ experts opined that a propane explosion in a home was

caused by copper-sulfide contamination of the safety valve seat of a water heater. Id.

at 1231. The defendants sought to exclude the plaintiffs’ experts for, among other

reasons, failure to test their theory that copper sulfide had passed through a mesh

screen to lodge on the safety valve seat. Id. at 1235. The district court declined to

exclude the plaintiffs’ experts, and this court affirmed. We observed that the experts’

theory of the accident was based on the “known science of copper sulfide particulate

contamination as a cause of propane gas leaks” and that testing of this established

scientific principle would normally be unnecessary. Id. at 1236. We reasoned that

while the presence of a mesh screen designed to filter out those particles changed the

causal analysis, it did not “fundamentally and necessarily change[] the nature of the

underlying science.” Id. Thus, because the “core science—that copper sulfide

particles are the kind of thing that when lodged on the valve seat can cause leaks—

[was] sufficiently well-established,” we concluded that testing was not required to

                                             17
permit the plaintiffs’ experts to opine that the particles actually found were of

sufficient size to cause a leak. Id.

       Here, the Tabers have not identified a known and undisputed scientific

principle or theory that demonstrates testing was unnecessary to establish the

reliability of Dr. Purswell’s opinion. The Tabers’ briefing states only that Dr.

Purswell’s testimony is based on “accepted standards and practices,” his “expertise

and training,” and the “biomechanics of a person.” But these generalities do not even

approach the specific scientific principles underlying the district court’s decision in

Bitler. Indeed, the Tabers have directed us to no “known science” relating to the

cause of falls from ladders whose dimensions or geometry exceed OSHA and ANSI

specifications. To the contrary, Dr. Purswell conceded he was unaware of any

published articles or literature regarding irregularly constructed ladders or studies

analyzing the rate of fall from ladders that failed to comply with OSHA or ANSI

standards. Absent a demonstration that Dr. Purswell’s theory was based on an

undisputed scientific principle, we cannot conclude the district court abused its

discretion by finding the reliability of the theory should have been established

through testing.

       b. Failure to Exclude Alternative Explanations

       The Tabers also challenge the district court’s conclusion that Dr. Purswell

failed to exclude alternative causes of Mr. Taber’s fall. In evaluating an expert’s

testimony, district courts may consider whether the expert has “adequately accounted

for obvious alternative explanations.” Fed. R. Evid. 702 committee note to 2000

                                           18
amendment. But an expert need not exclude every possible cause of an injury to

testify as to causation. Bitler, 400 F.3d at 1238 n.6. Instead, the expert need only

exclude those alternative explanations that are “obvious”—i.e., where there is “an

established connection between certain possible causes and [the injury].” Id. If there

is no evidence showing a possible alternative is valid, the expert’s failure to rule it

out does not render his diagnosis unreliable. Goebel v. Denver & Rio Grande W. R.R.

Co., 346 F.3d 987, 999 (10th Cir. 2003). So long as the most obvious causes have

been considered and ruled out, the existence of possible “uneliminated” causes goes

to “the accuracy of the conclusion, not the soundness of the methodology,” and

therefore goes to the weight rather than admissibility of the evidence. Ambrosini v.

Labarraque, 101 F.3d 129, 140 (D.C. Cir. 1996).

       In Bitler, we referred to this process of eliminating causes to arrive at the most

likely as “reasoning to the best inference,” and we analogized the process to the

medical practice of “differential diagnosis.” 400 F.3d at 1237. In taking this

approach, the expert must first identify “some independent evidence that the cause

identified is of the type that could have been the cause.” Id. The expert must then

“eliminate other possible sources as highly improbable, and must demonstrate that

the cause identified is highly probable.” Id. at 1238. Applying those principles to the

facts of Bitler, we stated, “[I]t is uncontroverted that if copper sulfide particles of

sufficient size became lodged on the safety valve seat, then a gas leak substantial

enough to cause the explosion . . . could occur.” Id. And we observed that the experts

had “testified to how they eliminated the gas leaks in the bedroom and the T-

                                            19
connector above the water heater as likely sources of the accident; the one was not

located close enough to the source of the explosion, and the other was itself most

likely the result of trauma caused by the explosion.” Id. at 1237. With the experts’

cause independently identified and the alternative causes eliminated as highly

improbable, we concluded the experts had engaged in reasoning that identified the

copper-sulfide contamination of the safety valve as the best inference of causation,

thereby providing sufficient reliability for the admission of their opinions. Id. at

1238.

        Here, Allied moved to exclude Dr. Purswell’s opinion, in part, because he

failed to address alternative causes of the fall: Mr. Taber’s “history of seizures, the

worn condition of his boots, the possibility that he had contaminants on his gloves or

boots that caused him to slip, or that he just lost his balance.” In opposing this

argument, the Tabers did not argue that Dr. Purswell had conducted an appropriate

“differential diagnosis” or “reasoning to the best inference.” Rather, the Tabers’

position below was that Dr. Purswell had “considered other sources” for the fall and

that he “would have criticisms for improper footwear” and “agreed that if a seizure

occurred then that could have caused the fall.” Because “[t]hese are not flat out

refusals to consider alternative possibilities,” the Tabers contended Dr. Purswell’s

determination that the ladder caused Mr. Taber’s fall was reliable. Thus, in the

district court, the Tabers argued that it was sufficient for Dr. Purswell to have

acknowledged the possibility of other causes, even if he was unable to eliminate

those causes as highly improbable.

                                           20
      Yet mere acknowledgment of other possible causes cannot establish the

reliability of Dr. Purswell’s causation theory. Rather, “reasoning to the best

inference” means that the expert “must eliminate other possible sources as highly

improbable, and must demonstrate that the cause identified [by the expert] is highly

probable.” Bitler, 400 F.3d at 1238. In his deposition, Dr. Purswell was asked, “Did

anything else cause or contribute to Mr. Taber’s fall?” Dr. Purswell testified that he

“wasn’t asked to look at that” and “ha[d] not done that.” Dr. Purswell agreed that Mr.

Taber’s fall could have been caused by “bad boots,” “stuff on his gloves,” “a

seizure,” or that “he just fell.” And while Dr. Purswell testified that he did not think

any of those causes were “the most likely reason” for Mr. Taber’s fall, his stated

basis for that opinion was “the very much out-of-standard geometry of the ladder.”

While this explanation may show that Dr. Purswell considered the non-compliant

geometry of the ladder to be a “highly probable” cause of Mr. Taber’s accident, it

does not demonstrate that Dr. Purswell ruled out other possible causes as “highly

improbable.” Id. Indeed, Dr. Purswell conceded he could not offer an opinion as to

other potential causes of the fall without resorting to speculation.

      The Tabers now contend Dr. Purswell did rule out “other possibilities, such as

[Mr. Taber’s] boots and/or alleged seizure condition.” They direct us to evidence that

a different expert had opined Mr. Taber did not suffer from a seizure disorder and

that Dr. Purswell examined Mr. Taber’s boots and concluded the worn areas would

not have been in contact with the ladder. But the Tabers did not argue these points or

direct the district court to this evidence in opposing Allied’s Daubert motion. And

                                           21
there is no indication that Dr. Purswell incorporated this information into his opinion.

Accordingly, Dr. Purswell could only speculate that the design of the ladder caused

Mr. Taber’s fall, and his opinion was therefore not reliable.

      Because the district court did not abuse its discretion in determining Dr.

Purswell’s testimony was unreliable based on his failure to test his theory or to

eliminate other possible causes, we affirm the district court’s exclusion of Dr.

Purswell’s testimony.

                          B. Grant of Summary Judgment

      Having affirmed the district court’s exclusion of the Tabers’ expert witnesses,

we now consider whether the Tabers’ claims can withstand summary judgment

absent expert testimony on the issue of causation. “We review the grant of summary

judgment de novo applying the same standard as the district court embodied in Rule

56(c).” Adler v. Wal-Mart Stores, Inc., 144 F.3d 664, 670 (10th Cir. 1998). “In

applying this standard, we view the factual record and draw all reasonable inferences

therefrom most favorably to the nonmovant.” Id. Summary judgment is proper “if the

movant shows that there is no genuine dispute as to any material fact and the movant

is entitled to judgment as a matter of law.” Fed. R. Civ. P. 56(a). Thus, summary

judgment is appropriately entered “against a party who fails to make a showing

sufficient to establish the existence of an element essential to that party’s case, and

on which that party will bear the burden of proof at trial.” Celotex Corp. v. Catrett,

477 U.S. 317, 322 (1986). Once the moving party meets its burden of demonstrating

the absence of a genuine issue of material fact, it is entitled to summary judgment if

                                           22
“the nonmoving party has failed to make a sufficient showing on an essential element

of her case with respect to which she has the burden of proof.” Id. at 323.

      A federal court sitting in diversity applies the substantive law of the forum

state, in this case, Oklahoma.2 Cornhusker Cas. Co. v. Skaj, 786 F.3d 842, 850 (10th

Cir. 2015). Under Oklahoma law, a premises-liability claim is a species of

negligence, generally arising from the allegation that the landowner failed to “keep

the premises in a reasonably safe condition” for invitees. Scott v. Archon Grp., L.P.,

191 P.3d 1207, 1212 (Okla. 2008). Thus, the Tabers must demonstrate Allied owed

Mr. Taber a duty to keep its premises reasonably safe, Allied breached that duty, Mr.

Taber suffered injury, and Mr. Taber’s injury was proximately caused by breach of


      2
          In contrast, a federal court applies its own procedural rules even when sitting
in diversity. Shady Grove Orthopedic Assocs., P.A. v. Allstate Ins. Co., 559 U.S. 393,
417 (2010). Whether summary judgment should have been granted in this federal
diversity case is therefore governed by the standard found in the Federal Rules of
Civil Procedure as applied to Oklahoma’s substantive law. C.F. Braun & Co. v. Okla.
Gas & Elec. Co., 603 F.2d 132, 133 n.1 (10th Cir. 1979) (“The propriety of summary
judgment in federal diversity cases must be evaluated in light of the Federal Rules of
Civil Procedure rather than state procedural law, but with reference to the state’s
substantive law.”). As a result, the Tabers’ reliance on Holland v. Urban
Contractors, Inc., 131 P.3d 139 (Okla. Civ. App. 2005), is misplaced. In Holland, the
Oklahoma Court of Civil Appeals denied a motion for summary judgment despite the
plaintiff’s failure to establish causation because, under Oklahoma’s rules of civil
procedure, “[i]t is not enough to show the likelihood that plaintiff will be unable at
trial to provide evidence to [] prove the essential elements of the cause of action.” Id.
at 141. But the summary-judgment standard under the federal rules governs here and
requires more. As the Supreme Court instructed in Celotex, the nonmoving party’s
failure to “make a sufficient showing on an essential element of her case with respect
to which she has the burden of proof” is fatal to her claim. 477 U.S. at 323. The
district court correctly applied the federal summary-judgment rules to conclude the
Tabers’ failure to come forward with causation evidence entitled Allied to summary
judgment.

                                           23
that duty. Beugler v. Burlington N. & Santa Fe Ry. Co., 490 F.3d 1224, 1227 (10th

Cir. 2007). In moving for summary judgment, Allied argued the Tabers could not

demonstrate the essential element of causation once their experts were excluded.3 The

district court agreed, reasoning “it is undisputed that Mr. Taber does not know why

he fell and there are no witnesses to the accident.” Because the Tabers lacked any

direct evidence of causation, the district court concluded they could establish

causation only through expert testimony. Accordingly, the district court granted

summary judgment in favor of Allied.

      The Tabers argue the district court erred because Mr. Taber’s own testimony

provided direct evidence of the cause of his fall. Pointing to his deposition, they

contend Mr. Taber explained that, as he was stepping down to reach the first

excessively spaced rung, he experienced a sensation of falling and attempted to hang

onto the ladder with one hand. But the Tabers failed to set forth this testimony in

their opposition to Allied’s motion for summary judgment. In its motion for summary

judgment, Allied asserted, “Taber was found unconscious lying on the ground

beneath the ladder, and had no memory of how he fell,” and “Taber further testified

that exactly what caused him to fall is a mystery.” The Tabers failed to challenge

either of these contentions in opposition to summary judgment. Instead, they first

brought Mr. Taber’s deposition testimony to the district court’s attention and first


      3
        Allied Waste also moved for summary judgment on the basis that the Tabers’
claims were barred by Oklahoma’s construction statute of repose. The district court
did not reach that issue and our disposition of the appeal on other grounds renders
consideration of the issue unnecessary.
                                           24
disputed Allied’s factual assertions in their Rule 59(e) motion. As discussed above,

we review the district court’s grant of summary judgment “from the perspective of

the district court at the time it made its ruling, ordinarily limiting our review to the

materials adequately brought to the attention of the district court by the parties.”

Adler, 144 F.3d at 671. We accordingly do not consider the evidence the Tabers

presented to the district court after the court had granted summary judgment in favor

of Allied. Based on what was before it, the district court did not err in concluding the

Tabers had “failed to make a sufficient showing on an essential element of [their]

case.” Celotex, 477 U.S. at 323. The district court therefore properly granted

summary judgment in favor of Allied.

                                  IV. CONCLUSION

       The Tabers failed to provide the district court with sufficient indicia of Dr.

Block’s qualifications and the reliability of Dr. Purswell’s opinion, and the district

court properly excluded their testimony. In the absence of that expert testimony, the

Tabers had no evidence to prove the condition of the ladder proximately caused Mr.

Taber’s fall. The district court therefore correctly concluded the Tabers could not

establish a required element of their claim and Allied was entitled to judgment as a

matter of law. We accordingly AFFIRM the district court’s summary judgment

decision.

                                             Entered for the Court


                                             Carolyn B. McHugh
                                             Circuit Judge
                                            25
