                                                                      F I L E D
                                                                United States Court of Appeals
                                                                        Tenth Circuit

                                                                        DEC 6 2004
                                        PUBLISH

                   UNITED STATES COURT OF APPEALS                  PATRICK FISHER
                                                                            Clerk
                                TENTH CIRCUIT



 FRED D. BITLER; PEGGY A.
 BITLER; COLORADO
 COMPENSATION INSURANCE
 AUTHORITY, a political subdivision
 of the State of Colorado,

              Plaintiffs - Appellees,

 v.

 A.O. SMITH CORPORATION, a
 foreign corporation; NATIONAL                       No. 02-1527
 PROPANE CORP., formerly known as
 All Seasons Propane, a Colorado
 corporation,

              Defendants,

        and

 WHITE RODGERS, a subsidiary of
 EMERSON ELECTRIC CORP., a
 foreign corporation,

              Defendant - Appellant.


                 Appeal from the United States District Court
                         for the District of Colorado
                   (D.C. Nos. 98-N-1897 and 98-BB-1897)


Daniel A. Nelson (Bruce A. Lampert, with him on the briefs), Schaden, Katzman,
Lampert & McClune, Broomfield, Colorado, for Plaintiffs-Appellees Fred and
Peggy Bitler.

Andrew M. Low (Peter J. Krumholz, with him on the briefs), Davis, Graham &
Stubbs LLP, Denver, Colorado, for Defendant-Appellant.


Before LUCERO, McKAY, and HARTZ, Circuit Judges.


LUCERO, Circuit Judge.


      Danger lurked in Fred and Peggy Bitler’s basement, liability for which is

the occasion for the present appeal. Mr. Bitler was severely burned when a gas

explosion occurred in the basement of his home. On filing a products liability

suit against, inter alia, White-Rodgers as manufacturer of the gas control installed

in his basement water heater, a jury returned a verdict finding negligence and

product defect and awarded damages to the Bitlers. White-Rodgers’ motions for

JNOV and a new trial having been denied by the district court, the present appeal

followed. In contesting the jury verdict imposing products liability on it for the

explosion, White-Rodgers assigns as principal error the district court’s admission

of plaintiffs’ expert testimony under Daubert principles. We exercise jurisdiction

under 28 U.S.C. § 1291 and AFFIRM.


                                         I

      Fred and Peggy Bitler resided in a house provided for their use on the


                                         2
Oldland Ranch outside of Meeker, Colorado where Fred Bitler was a ranch hand.

On the evening of the accident, July 25, 1996, Bitler discovered that there was no

hot water when he attempted to shower. Hot water was supplied to the Bitlers’

home by a liquid propane hot water heater located in the basement. Donning

sweat pants, he proceeded to the basement door, unlatched it, and walked

approximately two-third’s of the way down the staircase when a large explosion

occurred, knocking him backwards. His wife, Peggy Bitler, was thrown off a sofa

and onto the floor, which was later determined to have been raised several inches

by the force of the explosion. Fred Bitler sustained severe burns, and after being

flown by helicopter to a hospital, underwent multiple skin graft surgeries over the

following weeks. It was established at trial that he has, in addition to general

disfigurement, continuing problems with regulation of his body temperature, use

of his hands, growth of hair follicles, and he will also need additional procedures

in the future to develop nail growth on his hands. As a result of the injuries he

sustained in this accident, he is no longer able to perform the duties appertaining

to his former occupation as a cowboy and ranch hand.

       There were three gas propane appliances in the Bitlers’ home – a cook

stove in the kitchen, a furnace in a bedroom, and a space heater in one of the

bedrooms. Gas was supplied to the water heater via unsupported, flexible copper

tubing that ran along the basement ceiling joints. A “T-fitting” was located above


                                         3
the hot water heater which provided branches running to the hot water heater and

the space heater. Post-accident inspection revealed a minor leak at the inlet to the

bedroom heater, and a leak at the “T-connector.”

         White-Rodgers, a subdivision of Emerson Electric Co., manufactured the

water heater gas control used in the Bitlers’ hot water heater. This gas control

regulates the flow of gas to the pilot and main burner of the water heater, and is

designed to fulfill a crucial safety role if the pilot light is extinguished. To avoid

a gas leak that could lead to an explosion or fire, the gas control is designed to

shut off all gas flow to the pilot when the pilot is extinguished. As is well

known, a lit pilot heats a thermocouple which in turn creates an electric current

energizing an electromagnet that holds the safety valve open against the force of a

spring. So long as the pilot is lit, the safety valve remains open. If the pilot goes

out, however, the thermocouple will no longer be heated and will no longer

produce a current to energize the electromagnet, allowing the spring to snap the

valve shut. The safety valve seat is made of rubber, and is designed to create a

seal against a circular metal surface when closed to prevent the flow of gas to the

pilot.

         Copper sulfide is a frequent contaminate found in gas and propane lines. If

copper sulfide particles of sufficient size become lodged on a safety valve seat

when a pilot is extinguished, the particles may prevent the valve from sealing,


                                           4
resulting in a gas leak. It was established that numerous accidents have occurred

in this manner, and that copper sulfide contamination was a significant source of

concern for White-Rodgers. As a consequence, White-Rodgers modified the

design of the safety valve in 1978 and began installing a wire mesh screen in the

gas inlet, upstream from the safety valve to prevent copper sulfide particles from

migrating onto the rubber valve seat. In further recognition of the safety hazard

caused by copper sulfide contamination, White-Rodgers recalled all gas controls

lacking the mesh screen in 1980. Thereafter, White-Rodgers also began adding

another safety feature to the mesh screen by installing a deflection “baffle” to aid

in preventing debris from reaching the valve and to hold the edges of the mesh

screen in place more effectively. The safety valve installed in the Bitler’s water

heater was one of about 200,000 devices produced in the interim that contained

the mesh screen, but did not contain the baffle.

      As a result of their investigations, plaintiffs’ expert Elden Boh concluded

that the water heater was the source of the accident, and plaintiffs’ expert Donald

Sommer concluded that the leak was caused by copper sulfide contamination on

the water heater’s safety valve seat. Elden Boh is a fire investigator hired by the

Colorado Farm Bureau, and Donald Sommer is an engineer and accident

investigator retained by the Bitlers. Although White-Rodgers contests the

admissibility of these two experts on appeal, plaintiffs’ expert W. Alan


                                          5
Bullerdiek, a chemical engineer, also testified concerning the history of copper

sulfide-contamination-related accidents, and that the amount of contamination

found on the Bitlers’ safety valve seat was at an unacceptable level.

      During post-accident testing of the safety valve installed in the Bitlers’

water heater, the device was disassembled in the presence of representatives of

both White-Rodgers and the Bitlers. Copper sulfide particulate contamination

was discovered downstream of the mesh screen and found on the safety valve

seat. During the teardown, a test of the valve revealed that it snapped shut as

designed. Plaintiffs’ expert, Donald Sommer, opined at trial that a mix of copper

sulfide particles and grease located on the safety valve seat caused the leak. Mr.

Sommer testified that the valve seat was altered after the accident when the

control was turned to the “off” position; furthermore, he testified that because

copper sulfide contamination leads to intermittent leaks, the teardown test could

not be determinative. Whether the particles found on the safety valve were large

enough or of sufficient quantity to have caused the gas leak in the present case is

hotly disputed.

      Having marshaled their expert witnesses and having ruled out to their

satisfaction all other sources of the gas leak save for the gas control on the water

heater, the Bitlers filed suit in Colorado State Court against White-Rodgers, as

well as A.O. Smith Corporation, which manufactured the water heater, and


                                          6
National Propane Corporation, which installed and maintained the water heater

and propane piping in the house. After removing the case to federal district court,

defendants moved for summary judgment, contesting the admission of the

plaintiffs’ expert testimony as insufficiently reliable and lacking a firm

foundation in science. In an order denying the motion, the trial judge found that

the Bitlers’ proposed expert testimony was relevant and reliable in accord with

the standard required by Daubert v. Merrell Dow Pharms., Inc., 509 U.S. 579

(1993). The matter proceeded to a two-week jury trial, at the close of which the

jury returned a verdict against White-Rodgers and National Propane, attributing

fifty percent of the fault to National Propane and forty percent to White-Rodgers,

and awarding $2,319,492.27 in damages to the Bitlers. As to White-Rodgers

specifically, the jury found both negligence and product defect. In its order of

October 30, 2002, the district court denied White-Rodgers’ motions for judgment

as a matter of law and for a new trial. This appeal followed.

                                         II

      We review de novo whether the district court properly performed its role as

“gatekeeper” in admitting or excluding expert testimony. Dodge v. Cotter Corp.,

328 F.3d 1212, 1223 (10th Cir. 2003) (“Though the district court has discretion in

how it conducts the gatekeeper function, we have recognized that it has no

discretion to avoid performing the gatekeeper function.”). We review for abuse


                                          7
of discretion the manner in which the district court exercises its Daubert

“gatekeeping” role in making decisions whether to admit or exclude testimony.

General Elec. Co. v. Joiner, 522 U.S. 136, 139 (1997). We will not, however,

disturb a district court’s ruling absent our conviction that it is arbitrary,

capricious, whimsical, manifestly unreasonable, or clearly erroneous. Goebel v.

Denver and Rio Grande W. R.R. Co., 346 F.3d 987, 990 (10th Cir. 2003). The

district court must, however, make specific factual findings on the record which

are sufficient for an appellate court to review the trial court’s conclusion

concerning whether the testimony was scientifically reliable and factually

relevant. Dodge, 328 F.3d at 1223. Our standard of review of a trial court’s

factual findings in pursuit of its gatekeeping role does not vary when examining

exclusion or admission of expert testimony. Our focus on review mirrors that of

the trial judge’s assessment of the testimony itself: we are concerned with the

trial court’s performance of its obligation under Rule 702 and Daubert, not upon

the exact conclusions reached to exclude or admit expert testimony. See Goebel,

346 F.3d at 1001 (holding that district court did not abuse its discretion in

admitting expert testimony); Mitchell v. Gencorp Inc, 165 F.3d 778, 784 (10th

Cir. 1999) (holding that the district court did not abuse its discretion in excluding

expert testimony). Thus, although the district court “must, on the record make

some kind of reliability determination,” United States v. Velarde, 214 F.3d 1204,


                                            8
1209 (10th Cir. 2000), we recognize the wide latitude a district court has in

exercising its discretion to admit or exclude expert testimony.

                                           A

      White-Rodgers assigns as a principal source of error the district court’s

performance of its Daubert gatekeeping functions. We begin our inquiry into the

admissibility of the Bitlers’ expert testimony with Fed. R. Evid. 702. In accord

with Rule 702, the Supreme Court has determined that the trier of fact “must

ensure that any and all scientific testimony or evidence is not only relevant, but

reliable.” Daubert, 509 U.S. at 589. To fulfill its gatekeeping role, a district

court must therefore conduct a two-part inquiry.

      First, a district court must determine if the expert’s proffered testimony –

whether it concerns scientific, technical, or other special knowledge – has “a

reliable basis in the knowledge and experience of his [or her] discipline.” Id. at

592; see also, Kuhmo Tire Co. v. Carmichael, 526 U.S. 137, 149 (1999) (holding

that Daubert’s general principles apply to all expert matters under Rule 702). By

conducting a preliminary inquiry into the expert’s qualifications and the

admissibility of proffered evidence, a district court fulfills its initial obligation

under Fed. R. Evid. 104(a) (“Preliminary questions concerning the qualification

of a person to be a witness . . . or the admissibility of evidence shall be

determined by the court”). To determine whether expert testimony is admissible


                                           9
requires a trial court to examine “whether the reasoning or methodology

underlying the testimony is scientifically valid . . . .” Daubert, 509 U.S. at 592-

93. In order to establish an expert’s testimony as reliable, we have held that:

      The plaintiff need not prove that the expert is undisputably correct or that
      the expert’s theory is “generally accepted” in the scientific community.
      Instead, the plaintiff must show that the method employed by the expert in
      reaching the conclusion is scientifically sound and that the opinion is based
      on facts which sufficiently satisfy Rule 702’s reliability requirements.

Mitchell, 165 F.3d at 781 (citation omitted).

      Providing guidance as to the kinds of factors that might bear on a judge’s

gatekeeping determination, the Supreme Court has suggested that a court

consider: (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.”

Daubert, 509 U.S. at 593-94. The Court has made clear, however, that this list is

neither definitive nor exhaustive and that a trial judge has wide discretion both in

deciding how to assess an expert’s reliability and in making a determination of

that reliability. Kuhmo Tire Co., 526 U.S. at 150, 152-53; see also Velarde, 214

F.3d at 1208-09. While these factors are most relevant in the context of a new

and novel scientific theory – asking if it has been tested, subjected to peer review

and publication, etc. – they do provide examples of the general kinds of issues a


                                          10
trial court need probe in light of its purpose of ensuring that an expert “employs

in the courtroom the same level of intellectual rigor that characterizes the practice

of an expert in the relevant field.” Kumho Tire, 526 U.S. at 152. Failure to

consider one, or even any, of these factors, albeit suggestive, will not be

dispositive of a district court’s failure to fulfill its gatekeeping role because that

role depends on the underlying factual circumstances of the particular case.

      Accordingly, a trial court’s focus generally should not be upon the precise

conclusions reached by the expert, but on the methodology employed in reaching

those conclusions. Daubert, 509 U.S. at 595. Although it is not always a

straightforward exercise to disaggregate method and conclusion, when 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. See Joiner, 522 U.S. at 146; Dodge, 328 F.3d at 1222. When

examining an expert’s method, however, the inquiry should not be aimed at “the

exhaustive search for cosmic understanding but for the particularized resolution

of legal disputes.” Daubert, 509 U.S. at 597. 1 Thus it is the specific relation


      1
         Determining whether proffered testimony is scientifically reliable can be
a considerable challenge for a trial judge. As Justice Breyer has noted, “this
requirement will sometimes ask judges to make subtle and sophisticated
determinations about scientific methodology and its relation to the conclusions an
expert witness seeks to offer – particularly when a case arises in an area where
the science itself is tentative or uncertain. . . .” Joiner, 522 U.S. at 147-48
                                                                          (continued...)

                                           11
between an expert’s method, the proffered conclusions, and the particular factual

circumstances of the dispute, and not asymptotic perfection, that renders

testimony both reliable and relevant.

      Second, in fulfilling its Daubert obligations a trial court must also conduct

a further inquiry into whether proposed testimony is sufficiently “relevant to the

task at hand.” Daubert, 509 U.S. at 597. Relevant evidence “means evidence

having any tendency to make the existence of any fact that is of consequence to

the determination of the action more probable or less probable than it would be

without the evidence.” Fed. R. Evid. 401. The Supreme Court has described the

consideration of relevant evidence as one of “fit.” Daubert, 509 U.S. at 591. A

trial court must look at the logical relationship between the evidence proffered

and the material issue that evidence is supposed to support to determine if it

advances the purpose of aiding the trier of fact. Even if an expert’s proffered

evidence is scientifically valid and follows appropriately reliable methodologies,

it might not have sufficient bearing on the issue at hand to warrant a

determination that it has relevant “fit.” Id. Testimony concerning the laws of


      1
        (...continued)
(Breyer, J., concurring). To fulfill this task, however, as Judge Posner has
observed, “we do not have to become philosophers of science and set forth the
necessary and sufficient conditions of ‘real’ science,” or endeavor to discover
“the essence of ‘science,’ if there is such an essence.” Rosen v. Ciba-Geigy
Corp., 78 F.3d 316, 318 (7th Cir. 1996). We may leave the philosophy of science
to the philosophers.

                                         12
quantum mechanics may be scientifically relevant, but may have no practical

relevance to testimony concerning the function and possible failure of a water

heater safety valve control. Evidence appropriate for one purpose, therefore, may

not be relevant for a different purpose, and it is the trial court’s task to make this

fitness determination.

                                           B

      In fulfilling its Daubert gatekeeping function, the district court, in its order

denying summary judgment to the defendants, focused on two expert witnesses

proposed by the Bitlers: Elden Boh and Donald Sommer. On reviewing the

record, we note that the actual testimony offered at trial does not differ in

material respects from either Boh’s or Sommer’s depositions as analyzed by the

district court on motions for summary judgment. Nonetheless White-Rodgers

argues that the magistrate judge was required to perform a gatekeeping role by

entertaining anew, during pre-trial proceedings, defendant’s objections to the

testimony of Sommer; the magistrate judge instead treated District Judge

Nottingham’s order denying summary judgment as law of the case, and refused to

consider de novo the issue of whether to admit the Bitlers’ expert testimony. It is

clear, however, that because White-Rodgers did not raise new issues concerning

the reliability of the Bitlers’ expert witnesses, the district court did not fail to

perform its Daubert role merely by refusing to reconsider the question of


                                           13
admissibility that had already been decided. Daubert does not require a district

court to linger at the “gate,” as if caught in Zeno’s paradox, unable to proceed to

the main trial without first conducting a series of mini-trials with regard to every

objection raised against a party’s expert witnesses.

      As to reliability regarding Boh’s testimony, the district court specifically

found that Boh’s methodology in reaching his conclusion about the cause of the

explosion was sound. Employing his experience and knowledge as a fire

investigator, Boh observed the physical evidence at the scene of the accident and

deduced the likely cause of the explosion. Although such a method is not

susceptible to testing or peer review, it does constitute generally acceptable

practice as a method for fire investigators to analyze the cause of fire accidents.

See Kumho Tire Co., 526 U.S. at 150 (“the relevant reliability concerns may

focus upon personal knowledge or experience”). Nothing in Rule 702 or Daubert

requires more. We conclude that the trial court did not abuse its discretion in

finding Boh’s personal experience, training, method of observation, and deductive

reasoning sufficiently reliable to constitute “scientifically valid” methodology.

      With regard to the testimony of Donald Sommer, as well as other experts

testifying for the Bitlers, White-Rodgers argues that his testimony constituted

impermissible speculation because he failed to test his theory that copper sulfide

particles passed through and around the mesh screen to lodge on the safety valve


                                          14
seat and thereby cause the gas leak. Furthermore, White-Rodgers argues that

Sommer’s theory fails to “fit” the known facts that no particles of sufficient size

to cause a leak were found on the seat of the valve. Finally, White-Rodgers

contests the reliability of the so-called “differential diagnosis” method Sommer

employed.

      We turn to the issue whether the Bitlers’ experts, particularly Sommer,

were required to test their theory. No doubt, Daubert noted that a key factor in

valid scientific methodology is the practice of testing hypotheses to determine

whether they can be falsified. Daubert, 509 U.S. at 593 (citing Karl Popper,

Conjectures and Refutations: The Growth of Scientific Knowledge (5th ed. 1989),

who emphasized the importance of testing scientific theories to determine whether

they can withstand critical scrutiny). One object of Popper’s method of

falsification as a way of testing a scientific theory is to acknowledge that any

scientific theory is subject to future refutation through further observation and

testing. Popper’s emphasis, however, is aimed at theories purporting to explain

the causal relations among regularly occurring natural phenomena. (Ptolemy’s

theory of the movement of celestial bodies which hypothesized that the Earth was

the center of the solar system, later falsified by Copernicus, is a prominent

example of such a scientific theory subject to falsification by further inquiry.)

Although we would not conclude from the citation to Popper, or the logical


                                          15
positivist Carl Hempel, id. at 593, that the Supreme Court intended to limit a

district court’s consideration of whether testing would assist the trier of fact only

to those instances of scientific knowledge aimed at such causal relations, we do

find the emphasis suggested by the citations instructive.

      For example, in Truck Ins. Exch. v. Magnetek Inc., 360 F.3d 1206, 1211-

1212 (10th Cir. 2004), plaintiff attempted to introduce evidence of a novel theory,

“pyrolysis,” which hypothesized that wood could ignite at temperatures much

lower than normal under particular circumstances. We affirmed the district

court’s decision to exclude this evidence because plaintiff’s experts had failed to

test their novel theory sufficiently to demonstrate its scientific reliability. Id. at

1213. When an expert proposes a theory that modifies otherwise well-established

knowledge about regularly occurring phenomenon, such as the normal ignition

temperature of wood, we would expect the importance of testing as a factor in

determining reliability to be at its highest. Here, by contrast, plaintiffs’ experts

propose a theory about how the accident occurred given the known science of

copper sulfide particulate contamination as a cause of propane gas leaks. What

distinguishes the present case is that the need for testing is not at its highest

because the reliability of the science of copper sulfide contamination is not in

dispute, and thus the district court did not abuse its discretion in finding that the

presence of a screen did not alter the reliability of the fundamental science.


                                           16
      Whether the Bitlers established that the copper sulfide particles and grease

found on the valve seat caused this accident is a matter the district court

determined goes to the sufficiency of the evidence – not its scientific reliability.

Defendants misunderstand what is at stake in a reliability analysis when they

claim that the mere addition of a screen fundamentally and necessarily changed

the nature of the underlying science such that the district court abused its

discretion in admitting plaintiffs’ expert testimony. No doubt, presence of the

screen changed the causal analysis the jury was required to conduct based on the

conflicting evidence presented, but the presence of a screen did not change the

analysis into one that necessarily required further testing to determine its

scientific reliability. The core science – that copper sulfide particles are the kind

of thing that when lodged on the valve seat can cause leaks – is sufficiently well-

established that the district court did not abuse its discretion in finding it reliable.

The core dispute – whether copper sulfide particles found on the valve seat in this

case were sufficient to cause a leak – is one the district court could properly

determine is a question for the jury. In light of this evidentiary dispute, the

Bitlers need only establish by a preponderance of the evidence that copper sulfide

particles caused the gas explosion in their basement. See, e.g., Kaiser Found.

Health Plan v. Sharp, 741 P.2d 714, 719 (Colo. 1987). Had their experts

conducted further tests on their water heater’s safety valve and established by


                                           17
observation that it did intermittently fail, they may have established causation to a

near certainty. But such a high degree of certainty is not required. 2 Thus,

because testing is not necessary in all instances to establish reliability under

Daubert, and because the district court reasonably found that it was not required

by the particular factual circumstances of this case, we conclude that the district

court did not abuse its discretion in admitting the Bitlers’ experts’ testimony.

      With regard to White-Rodgers’ argument that the Bitlers’ experts

impermissibly relied on a method of “differential diagnosis,” we note that the

term is being used analogically to its proper use in a medical context; nonetheless,

we conclude that in this circumstance it is a valid scientific technique to establish

causation. 3 Concerning the method he employed in his investigation, Sommer

      2
        As to alleged shortcomings of the proffered testimony, these go to “the
weight which the trier of fact should accord the evidence and do not make the
testimony incredible.” Orth v. Emerson Elec. Co., 980 F.2d 632, 637 (10th Cir.
1992). Nowhere does Rule 702 or Daubert require a finding that an expert’s
proffered testimony reach absolute certainty with regard to the likely truth of a
conclusion. See Daubert, 509 U.S. at 590 (“Of course, it would be unreasonable
to conclude that the subject of scientific testimony must be ‘known’ to a certainty;
arguably, there are no certainties in science.”).
      3
         Urging us to adopt the analysis in Stibbs v. Mapco, 945 F.Supp. 1220 (D.
Iowa 1996), which also involved a LP gas explosion implicating one of their
controls, White-Rodgers argues that the inference involved in differential
diagnosis “turns scientific analysis on its head.” Id. at 1226. We reject this
reasoning as itself fundamentally unsound as we explain infra. Furthermore, we
adopt the district court’s apt analysis distinguishing Stibbs on its facts from the
present case – viz., in Stibbs the plaintiff’s evidence consisted of a mark on the
safety valve and the absence of a leak elsewhere, with no evidence of debris
                                                                         (continued...)

                                          18
testified that he undertook a process of eliminating alternative possible causes,

determining that these possibilities were improbable sources of the explosion, and

arriving at a highly probable cause for the gas leak, calling it a method of

“differential diagnosis.” “Differential diagnosis,” is “the determination of which

of two or more diseases with similar symptoms is the one from which the patient

is suffering, by a systematic comparison and contrasting of the clinical findings.”

Stedman’s Medical Dictionary 492 (27th ed. 1995). 4 In the medical context,

differential diagnosis is a common method of analysis, and federal courts have

regularly found it reliable under Daubert. Goebel, 346 F.3d at 999 (concluding

that a district court may admit a differential diagnosis it determines is reliable);

Westberry v. Gislaved Gummi AB, 178 F.3d 257, 262 (4th Cir. 1999) (holding

that differential diagnosis is a reliable technique “of identifying the cause of a

medical problem by eliminating the likely causes until the most probable one is

isolated”); Clausen v. M/V New Carissa, 339 F.3d 1049, 1058-59 (9th Cir. 2003)

(recognizing differential diagnosis as a reliable method); Zuchowicz v. United

States, 140 F.3d 381, 387 (2d Cir. 1998) (upholding district court decision to



      (...continued)
      3

downstream nor testimony as to how debris could have migrated past the screen.
      4
         Used in its traditional medical sense, the term refers “to the diagnosis of
disease, and refers to the process of identifying external causes of diseases and
conditions as ‘determining cause’ . . . as the circumstances warrant.” Federal
Judicial Center, Reference Manual on Scientific Evidence 444 (2d ed. 2000).

                                          19
admit differential diagnosis testimony). What is not so clear is whether

“differential diagnosis” is an appropriate method when employed outside of the

medical context.

      Here, however, the Bitlers’ experts use a general method more aptly

characterized as a process of reasoning to the best inference. 5 The Bitlers’

experts must reason, as it were, backwards to the cause of a single explosion, and

to do so requires a process of eliminating possible causes as improbable until the

most likely one is identified. For example, Sommer and Boh both testified to how

they eliminated the gas leaks in the bedroom and the T-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. Sommer testified that the force of the explosion

lifted the house off its foundation, and accordingly, was the most probable cause

of the leak at the T-connector, especially in light of its damaged physical

condition. Experts must provide objective reasons for eliminating alternative

causes when employing a “differential analysis.” See Clausen, 339 F.3d at 1058.


      5
         Unlike a logical inference made by deduction where one proposition can
be logically inferred from other known propositions, and unlike induction where a
generalized conclusion can be inferred from a range of known particulars,
inference to the best explanation – or “abductive inferences” – are drawn about a
particular proposition or event by a process of eliminating all other possible
conclusions to arrive at the most likely one, the one that best explains the
available data.

                                         20
Furthermore, the inference to the best explanation must first be in the range of

possible causes; there must be some independent evidence that the cause

identified is of the type that could have been the cause. See Joiner, 522 U.S. at

146 (“[N]othing in either Daubert or the Federal Rules of Evidence requires a

district court to admit opinion evidence that is connected to existing data only by

the ipse dixit of the expert.”). But more than mere possibility, an inference to the

best explanation for the cause of an accident must eliminate other possible

sources as highly improbable, and must demonstrate that the cause identified is

highly probable. 6 In the present case, it 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 in the Bitlers’ basement could occur.

Whether or not that actually occurred is a question that may be answered by

inference to the best explanation. 7 We see no abuse of discretion, especially in

      6
         An expert must show that other causes are improbable when conducting
differential diagnosis, but “[t]his is not to say that an expert, in order to testify on
causation, must be able to categorically exclude each and every possible
alternative cause. . . .” – to require otherwise “would mean that few experts would
ever be able to testify.” Stephen A. Saltzburg et al., Federal Rules of Evidence
Manual 702–33 (8th ed. 2002). Indeed, “the underlying premise of differential
diagnosis is that there is an established connection between certain possible
causes and a condition or symptom—then all of the established causes are ruled
out but one.” Id. at 702–35.
      7
          As Judge Kozinski noted on remand in Daubert: “Not knowing the
mechanism whereby a particular agent causes a particular effect is not always
fatal to a plaintiff’s claim. Causation can be proved even when we don’t know
                                                                     (continued...)

                                          21
light of our deferential standard of review, in the district court’s admitting expert

testimony that employs an expert’s physical investigation, professional

experience, and technical knowledge to establish causation in this case.

      Finally, as to the “fit” between the expert testimony and the material issue

at stake in this case, White-Rodgers argues that the theory of copper sulfide

particulate contamination does not “fit” the facts that the safety valve at issue is a

screened valve, and no screened valve had ever been shown to allow sufficient

copper sulfide downstream so as to cause a gas leak; furthermore, the valve

functioned properly when tested after the accident. This argument confuses a

Daubert inquiry into relevant “fit” with the jury question of which theory,

plaintiffs’ or defendant’s, best captures the truth of the matter at issue. The

former inquiry is aimed at determining if “a valid scientific connection to the

pertinent inquiry,” Daubert, 509 U.S. at 592, obtains as a precondition to the

admissibility of expert testimony. Here, the expert testimony “fits” because it

involves a reliable method that would aid the jury in resolving a factual dispute;

whether the jury finds that the testimony “fits” their best assessment of the truth

of the matter is an altogether different issue. Accordingly, the district court did



      7
       (...continued)
precisely how the damage occurred, if there is sufficiently compelling proof that
the agent must have caused the damage. . . .” Daubert v. Merrell Dow Pharm., 43
F.3d 1311, 1314 (9th Cir. 1995).

                                          22
not abuse its discretion in admitting the Bitlers’ expert testimony.

      Thus, in summation, we conclude that in fulfilling its gatekeeping role

pursuant to the Federal Rules of Evidence and Daubert, the district court did not

abuse its discretion in making its “preliminary assessment of whether the

reasoning or methodology underlying the testimony is scientifically valid and of

whether that reasoning or methodology properly can be applied to the facts in

issue.” Daubert, 509 U.S. at 592-3.

                                         III

      White-Rodgers argues on appeal that safety valve models lacking an inlet

screen are substantially dissimilar from models containing the mesh screen and

therefore the district court abused its discretion in admitting plaintiff’s evidence

of accidents involving the unscreened devices.

      At trial, the Bitlers introduced evidence of accidents which involved a

model of safety valves exactly the same as the one in the Bitlers’ water heater

save for the absence of the inlet screen. These accidents occurred when copper

sulfide particles contaminated the safety valve of unscreened safety controls,

preventing the valve from closing fully and resulting in a gas leak. The purpose

of this evidence was to demonstrate a key element of the Bitlers’ theory of

causation: if copper sulfide particles are allowed downstream to contaminate the

valve seat, then the safety valve system could fail. Furthermore, the Bitlers argue


                                          23
that this evidence was necessary to prove notice to White-Rodgers of the potential

for their safety valves to fail.

       In response, White-Rodgers contends that they offered to stipulate to the

failures of the unscreened device, and that therefore the admission of evidence

involving accidents with unscreened controls was irrelevant. Although White-

Rodgers admits that copper sulphide particles can cause leaks in unscreened

models, they argue that there has been no demonstration that screened models are

susceptible to sufficient contamination to cause leaks; therefore, they suggest that

the presence of a screen makes the Bitlers’ safety control substantially dissimilar

to unscreened devices. Moreover, because these other accidents involving

unscreened controls resulted in injuries and deaths, White-Rodgers argues that the

evidence was inherently prejudicial.

       We review a district court’s decision to admit evidence for abuse of

discretion. Smith v. Ingersoll-Rand Co., 214 F.3d 1235, 1246 (10th Cir. 2000).

As a threshold matter, we will admit evidence of prior accidents in a products

liability suit if it is relevant to the present inquiry. Id. To determine relevancy,

we must examine whether there is substantial similarity between the evidence

offered of prior accidents and the facts at issue in the present case. “Before

introducing such evidence, the party seeking its admission must show the

circumstances surrounding the other accidents were substantially similar to the


                                          24
accident involved in the present case.” Wheeler v. John Deere Co., 862 F.2d

1404, 1407 (10th Cir. 1988); Black v. M & W Gear Co., 269 F.3d 1220, 1227

(10th Cir. 2001). Determining whether and to what extent proffered evidence of

prior accidents involves substantially similar circumstances will depend on the

underlying theory of the case advanced by the plaintiffs. If the evidence of other

accidents is substantially similar to the accident at issue in a particular case, then

that evidence will assist the trier of fact by making the existence of a fact in

dispute more or less probable, and the greater the degree of similarity the more

relevant the evidence. See Four Corners Helicopters, Inc. v. Paton, 979 F.2d

1434, 1440 (10th Cir. 1992). Naturally, this is a fact-specific inquiry that depends

largely on the theory of the underlying defect in a particular case. Id.

Accordingly, the district court is owed considerable deference in its determination

of substantial similarity.

      With regard to the Bitlers’ proposed evidence of accidents involving

unscreened devices, the district court ruled that these prior accidents involved

substantially similar devices to the one involved in the present accident, and

accordingly denied the defendant’s motion in limine to exclude. In order to

demonstrate notice and the existence of a defect, namely the consequences of

copper sulfide contamination, the district court ruled that exact similarity between

the devices was not required and its absence would not compel exclusion. We


                                           25
have routinely held that federal law permits introduction of substantially similar

accidents to show notice, the potential existence of a defect, or to refute defense

witness testimony. Four Corners Helicopters, Inc., 979 F.2d at 1440.

      In light of the plaintiffs’ purposes of showing notice and defect, we do not

require a showing of exact similarity, and hence we cannot conclude that the

district court erred in admitting evidence it found substantially similar given the

circumstances surrounding the Bitlers’ accident. In order to demonstrate that

copper sulfide particles were capable of causing a gas leak when contaminating

the safety valve seat, it was reasonable and relevant for the plaintiffs to introduce

evidence of failures in substantially similar devices under substantially similar

circumstances. If contamination could cause gas leaks absent an inlet screen,

then if the plaintiffs could show that particles could get through or around the

screen – the essence of the plaintiffs’ case – it would be reasonable for jurors to

make a determination as to causation in the present case. Offering evidence that

the industry was aware as early as 1967 that copper sulfide contamination could

be a problem for gas control valves served the purpose of demonstrating notice to

White-Rodgers and of highlighting the potential existence of a defect – part of the

underlying theory of the plaintiff’s case which goes to establish a standard in this

case for “how substantial the similarity must be. . . .” Ponder v. Warren Tool

Corp., 834 F.2d 1553, 1560 (10th Cir. 1987) (citation omitted). Indeed, the


                                          26
district court found that the similarity between the two models of safety valves,

for purposes of the trial, was not only substantial, but constituted a “high degree

of similarity” in light of other evidence demonstrating that even with the screen,

copper sulfide particles were found downstream from the screen. (4 R. at 967.)

      We see no error in the district court’s finding. Accordingly, we hold that

the district court did not abuse its discretion in admitting evidence of prior

accidents involving unscreened safety valves.

                                          IV

      White-Rogers argues that the district court erred by giving a jury

instruction on failure to warn of known and non-obvious defects in its safety

valve. Whether a jury was properly instructed in accord with the applicable law

and consistent with matters properly within its provence is a question we review

de novo. Gardetto v. Mason, 100 F.3d 803, 816 (10th Cir. 1996). However, we

will review for abuse of discretion a district court’s exercise of its discretion in

giving a particular jury instruction. Hynes v. Energy West, Inc., 211 F.3d 1193,

1197 (10th Cir. 2000).

      Arguing that the issue of a duty to warn was not supported by the evidence,

and hence not a matter properly submitted to the jury, White-Rodgers objects to

the district court’s presentation of the following instruction to the jury:

      If A.O. Smith and White-Rodgers, a wholly-owned division of Emerson
      Electric, as manufacturers or sellers of a product know or in the exercise of

                                          27
      reasonable care should know that the use of the product may be harmful or
      injurious to a user, and such risk of harm or injury is not obvious to a
      reasonable user, then the manufacturer and seller must use reasonable care
      to warn the user of the risk of harm or injury if a reasonably careful person
      would under the same or similar circumstances. The failure to do so is
      negligence.

(13 R. at 3525.)

      As a threshold matter, we are persuaded that White-Rodgers’ assignment of

error to the district court’s jury instruction on a duty to warn is not properly

preserved for appeal. At trial, White-Rodgers objected generally to the jury

instruction concerning a duty to warn, arguing only that there is neither a basis for,

nor an issue of, a failure to warn. 8 Defendant further objected that plaintiffs failed

to establish any evidence for the instruction. Rejecting White-Rodgers’ inchoate

objections, the district court found “that there is evidence sufficient to allow the

jury to determine that White-Rodgers knew prior to this accident of the migration

of copper sulfide around the screen only device, which the jury could conclude

required a duty to warn.” (12 R. at 3057-58.)

      On appeal, White-Rodgers now asserts that the jury instruction on a failure

to warn was error because plaintiffs presented no evidence of proximate causation.

Specifically, Appellant now argues that plaintiffs provided no evidence that a



      8
        White-Rodgers’ counsel opined generally: “If the product is found to be
defective then I guess liability exists. I don’t know what we’re supposed to warn
them about.” (11 R. 2995.)

                                           28
warning would have been effective or what the content of that warning would have

been. However, at trial Appellants did not raise an objection as to proximate

causation distinctly and did not identify specifically the grounds of the objection

before the district court as required by Fed. R. Civ. P. 51(c)(1) (“A party who

objects to an instruction or the failure to give an instruction must do so on the

record, stating distinctly the matter objected to and the grounds of the objection.”);

see also Hynes, 211 F.3d at 1200. White-Rodgers failed to make abundantly clear

the grounds and basis for its objection to the jury instruction on a failure to warn,

objecting instead in general terms that there was no issue of warning. See Weir v.

Fed. Ins. Co., 811 F.2d 1387, 1390 (10th Cir. 1987) (noting that Rule 51 “requires

counsel to make abundantly clear to the trial court the objecting party's position”)

(quotation omitted). To preserve an objection for appeal, it is not enough for an

objecting party merely to raise an objection. Instead, the “grounds stated in [an]

objection must be obvious, plain, or unmistakable.” Id. (citation omitted); see

also, Medlock v. Ortho Biotech, Inc., 164 F.3d 545, 553 (10th Cir. 1999) (noting

that “an excessively vague or general objection to the propriety of a given

instruction is insufficient to reserve the issue for appeal”).

      Accordingly, because White-Rogers’ objections were not properly specific,

the issue of supposed error in the district court’s jury instruction regarding failure

to warn is not properly preserved for appeal.


                                          29
                                          V

      In the alternative, failing success on its argument to reverse the jury verdict,

White-Rodgers argues that the jury award of $150,000 for future wage loss and

$75,000 for future medical expenses was not supported by any evidence. When we

review a jury’s award of damages, we will sustain the award unless it is clearly

erroneous or there is no evidence to support the award. Hudson v. Smith, 618 F.2d

642, 646 (10th Cir. 1980); Brown v. Presbyterian Healthcare Servs., 101 F.3d

1324, 1330 (10th Cir. 1996).

      With regard to the evidence of future wage loss, Mr. Bitler provided tax

returns for the years prior and subsequent to the accident and provided testimony

concerning his current employment prospects. There is no doubt that evidence was

presented that his earnings have declined as a consequence of the accident, and

that although he remains employable in some settings, his employment prospects

have been substantially diminished. Furthermore, evidence was also offered of

benefits he received as a ranch hand, but no longer receives, such as use of the

furnished house where the accident occurred and a replacement heifer worth $850,

that go beyond his salary as reflected by his tax returns. In light of our highly

deferential stance regarding jury determinations of damages, we cannot say that

there was no evidence presented to support a jury finding of future lost wages in

the amount of $150,000.


                                         30
      Concerning the evidence of future medical expenses, there is no doubt that

physician testimony and Mr. Bitler’s testimony did not establish precise costs of

any future procedures. One physician testifying, Dr. Hartford, described past

problems with infections involving Mr. Bitler’s skin grafts, and acknowledged a

possibility of future infections. Mr. Bitler’s plastic surgeon, Dr. Gordon, testified

to the future need for procedures to develop Mr. Bitler’s fingernails, which Bitler

has elected to defer to a later time. (3 R. at 768.) Plaintiff argues that the jury

could reasonably estimate future medical expenses based on the stipulation by the

parties to past medical expenses. Clearly, such a basis for determining an award

for future medical expenses is imprecise and on review is not based on specific

and substantial evidence. But we do not review for substantial evidence; rather,

we review for clear error whether there is any evidence to support the jury finding.

Despite some estimation in the jury’s award for future medical expenses, we

cannot conclude, in light of our deferential review, that there is no evidence to

support the award or that it was clearly erroneous.

      Therefore, as to the jury awards for future wage loss and future medical

expenses, we affirm.

                                          VI

      With regard to the final issue in White-Rodgers’ appeal, appellant argues

that the jury award of $25,000 for Mrs. Bitler’s physical and emotional injury was


                                          31
excessive. Specifically, White-Rodgers argues that negligent infliction of

emotional harm was not pled, and because Mrs. Bitler suffered only minor physical

injuries in the accident, that the jury award is clearly excessive. We disagree. As

appellant concedes, Mrs. Bitler may recover emotional injuries that flow from her

own physical injuries. See, e.g., Williams v. Continental Airlines, Inc., 943 P.2d

10, 16 (Colo. App. 1996). Because the circumstance surrounding her admittedly

minor physical injury to her knee when the force of the explosion in the basement

forced her off the sofa and onto the floor is itself quite traumatic, we cannot

conclude that the jury had no basis for finding the emotional injury associated with

her own experience of, and physical injuries from, the explosion – quite apart from

the emotional trauma of seeing the injuries sustained by her husband – are grossly

excessive. Accordingly, as to the jury’s damage award for Mrs. Bitler’s

negligence claim, we affirm.

                                         VII

      For the reasons set forth above, we AFFIRM.




                                          32
