                     United States Court of Appeals
                           FOR THE EIGHTH CIRCUIT
                                   ___________

                                   No. 01-1058
                                   ___________

Fred Lauzon,                         *
                                     *
           Plaintiff-Appellant,      *
                                     * Appeal from the United States
     v.                              * District Court for the
                                     * District of Minnesota.
Senco Products, Inc.,                *
                                     *
           Defendant-Appellee.       *
                                ___________

                             Submitted: August 21, 2001

                                  Filed: October 26, 2001
                                   ___________

Before BYE, LAY, and JOHN R. GIBSON, Circuit Judges.
                             ___________

LAY, Circuit Judge.

      In December 1997, Fred Lauzon, a carpenter, was injured while using Senco
Products, Inc. (“Senco”) bottom-fire pneumatic nailer, model SN2 (“SN2”). Lauzon
brought suit for negligence, breach of warranty, manufacturing defect, and design
defect against Senco for injuries that arose out of the use of the SN2.

       The design of the bottom-fire pneumatic nailer enables it to drive nails by two
different means. First, it can drive a single nail when the trigger and the bottom
contact point are depressed. Second, it can rapid-fire nails when the operator
depresses and holds the trigger and bounces the bottom contact point off the surface
of the work. Senco markets the bottom-fire pneumatic nailer for the second manner
of use, the rapid-fire mode.

       Senco produces a second type of pneumatic nailer, a sequential-fire tool. It
drives nails only one way, when the bottom contact element is depressed and the
trigger is subsequently pulled. Unlike the bottom-fire pneumatic nailer, the trigger
of the sequential-fire tool must be released and squeezed each time the user seeks to
fire a nail.

       Lauzon was using the SN2 to roof a garage. He was lying on the edge of the
roof while securing a fourteen-foot 2 x 6 to the roof sheathing. His left hand was
supporting the 2 x 6 under the overhang and his right hand was holding the SN2. A
fellow workman, Steve Nelson, was standing on a ladder underneath supporting the
2 x 6 Lauzon was attempting to secure.

       Lauzon testified that he properly drove a nail and as the SN2 recoiled, two
more nails were driven, the second one entering his hand. Lauzon acknowledges his
finger was on the trigger, it being constantly depressed as he was employing the
bottom-fire pneumatic nailer in its rapid-fire mode. Yet, he contends the SN2 should
not have fired successive nails because the bottom contact point was not depressed,
since it was four to five inches above the roof sheathing. Lauzon testified it was not
possible that the bottom contact point came into contact with the sheathing because
it would have shot the nails into the wood and not his thumb. However, he was
uncertain of all the details because “it happened so fast, it was–it was like, wow,
what–what happened you know.”

      In spite of his uncertainty, he states that the accident was not the result of a
“double-fire.” A double-fire occurs when the tool cycles twice before the user is able
to remove the bottom contact point from the surface of the work, thereby
unintentionally driving a second nail instantaneously after the first. Lauzon testified,

                                          -2-
although two nails were expelled, it was not a double-fire because the bottom contact
point was not depressed.

       His fellow worker, Nelson, submitted an affidavit, dated May 22, 2000, stating
he does not believe the SN2 double-fired, although he “could not say with absolute
certainty,” and alluded to the possibility that Lauzon may have been using the SN2
in a hazardous manner. In a second statement, dated June 16, 2000, Nelson modifies
his statement slightly. In this statement he claims he does not “specifically remember
one way or the other” whether the SN2 double-fired or misfired, although he does
“clearly remember that the safety tip of the nail gun was contacting the edge of the
wood.”

       Lauzon retained H. Boulter Kelsey as a proposed expert witness. Kelsey is a
licensed professional engineer in the State of Missouri by examination. He earned
a Bachelor of Science and a Master’s Degree in Mechanical Engineering from
Washington University in St. Louis, Missouri. From 1973 until 1980, Kelsey was
Assistant Dean at Washington University. For the past twenty years he has worked
as a forensic engineer. He has previously testified in approximately forty pneumatic
nail gun cases. See, e.g., Drabik v. Stanley-Bostitch, Inc., 997 F.2d 496 (8th Cir.
1993); Bailey v. Innovative Mgmt. & Inv., Inc., 890 S.W.2d 648 (Miss. 1994).

       Kelsey performed a number of tests and analyzed the circumstances
surrounding the injury. As a result of this analysis, Kelsey rendered an opinion:
“[g]iven the tests that were conducted, Mr. Lauzon’s recollection of the accident
occurrence is in error.” He stated that “Mr. Lauzon’s testimony that he believed the
gun was some 4 to 5 inches above the plywood surface when the accident occurred
can only be an error on his part.” Kelsey proposed a different interpretation of the
event.




                                         -3-
      It would appear that in the process of moving his body down the sloped
      roof surface, Lauzon unintentionally and unconsciously caused the nose
      trigger of the subject Senco nailer to contact the edge of the plywood
      roof sheathing. When this occurred, only a portion of the bottom fire or
      nose trigger engaged the edge of the plywood which allowed a nail to be
      fired into or just past the edge of the plywood. Since the nail that was
      fired was totally unintended and unconsciously driven by Mr. Lauzon’s
      movements, he undoubtedly experienced a second firing of the nailer
      due to recoil . . . . This second nail was driven in the same fashion with
      the nose trigger of the gun contacting the very edge of the plywood
      sheathing in such a manner as to allow the nail to be expelled past the
      sheathing and 2 x 6 and enter his hand below. Given the circumstanced
      [sic] described by Mr. Lauzon and the testing accomplished on the
      subject model SN2 Senco nailer, no other scenario of the accident can
      be reasonably deduced.

H. Boulter Kelsey, Expert Report, at 6. Kelsey’s conclusion that Lauzon’s injuries
were the result of a double-fire precludes the finding of a manufacturing defect,
leaving only the claim of a design defect.

       Kelsey opines the design of the SN2, a bottom-fire nailer, is defective because
of the propensity to double-fire, therefore, he concludes the SN2 was unreasonably
dangerous, and Lauzon’s injuries were the result of a double-fire. Further, Kelsey
opines the sequential-fire nailer is commensurate in its use to the bottom-fire nailer
but is much safer because its design ensures a double-fire cannot occur. As a result,
Kelsey proffers the inherently dangerous designed bottom-fire tool should no longer
be on the market.

      In applying the rules of Daubert v. Merrell Dow Pharm., 509 U.S. 579 (1993),
but without holding a pretrial Daubert hearing, the district court excluded Kelsey’s
expert testimony, finding insufficient evidence to sustain plaintiff’s case, and granted
summary judgment for the defendant. Daubert emphasizes that the district court is
the “gatekeeper” for the admissibility of expert testimony which, of course, is true

                                          -4-
when the district court passes upon the admissibility of any evidence. Our standard
of review is one of abuse of discretion, and in exercising this review, this court must
give great deference to the ruling of the trial court. Yet, as the Supreme Court
reminds us, it is the hallmark of our review, absent abdicating our duty, to analyze the
trial court’s ruling in light of the principles of Daubert and the Federal Rules of
Evidence.

I. Analysis

       Lauzon contends the district court erred by excluding the testimony of the
proposed expert witness, Kelsey. The abuse of discretion “standard applies as much
to the trial court’s decisions about how to determine reliability as to its ultimate
conclusion.” Kumho Tire Co., Ltd. v. Carmichael, 526 U.S. 137, 152 (1999). The
proponent of the expert testimony must prove its admissibility by a preponderance of
the evidence. Daubert, 509 U.S. at 592.

       Federal Rule of Evidence 702 governs admissibility of expert testimony. See
Fed. R. Evid. 702. “Rule 702 reflects an attempt to liberalize the rules governing the
admission of expert testimony.” Weisgram v. Marley Co., 169 F.3d 514, 523 (8th
Cir 1999) aff’d, 528 U.S. 440 (2000); see also Daubert, 509 U.S. at 588 (citing Beech
Aircraft Corp. v. Rainey, 488 U.S. 153, 169 (1988)) (highlighting the “‘liberal thrust’
of the Federal Rules and their ‘general approach of relaxing the traditional barriers
to ‘opinion’ testimony’”). The rule clearly “is one of admissibility rather than
exclusion.” Arcoren v. United States, 929 F.2d 1235, 1239 (8th Cir. 1991).

      The proposed expert testimony must meet three prerequisites in order to be
admitted under Rule 702. 4 Jack B. Weinstein & Margaret A. Berger, Weinstein’s
Federal Evidence § 702.02[3] (2001). First, evidence based on scientific, technical,
or other specialized knowledge must be useful to the finder of fact in deciding the
ultimate issue of fact. Id. This is the basic rule of relevancy. Second, the proposed

                                          -5-
witness must be qualified to assist the finder of fact. Id. Third, “the proposed
evidence must be reliable or trustworthy in an evidentiary sense, so that, if the finder
of fact accepts it as true, it provides the assistance the finder of fact requires . . . .”
Id.; see also Daubert, 509 U.S. at 591.

       The basis for the third prerequisite lies in the recent amendment of Rule 702,
which adds the following language to the former rule: “(1) the testimony is based
upon sufficient facts or data, (2) the testimony is the product of reliable principles and
methods, and (3) the witness has applied the principles and methods reliably to the
facts of the case.” Fed. R. Evid. 702.1 The language of the amendment codifies
Daubert and its progeny. Id. Comm. Note.

       In Daubert, the U.S. Supreme Court emphasized the district court’s gatekeeper
role when screening expert testimony for relevance and reliability. Daubert, 509 U.S.
at 591-93; see also Blue Dane Simmental Corp. v. Am. Simmental Ass’n, 178 F.3d
1035, 1040 (8th Cir. 1999) (during the evaluation “of expert testimony under Federal
Rule of Evidence 702, the district court must look to both the relevancy and the
reliability of the testimony”). Daubert provides a number of nonexclusive factors a
court can apply in performing this role: “(1) whether the theory or technique ‘can be
(and has been) tested’; (2) ‘whether the theory or technique has been subjected to peer


      1
          The complete, amended Fed. R. Evid. 702 provides:

               If scientific, technical, or other specialized knowledge will
               assist the trier of fact to understand the evidence or to
               determine a fact in issue, a witness qualified as an expert
               by knowledge, skill, experience, training, or education,
               may testify thereto in the form of an opinion or otherwise,
               if (1) the testimony is based upon sufficient facts or data,
               (2) the testimony is the product of reliable principles and
               methods, and (3) the witness has applied the principles and
               methods reliably to the facts of the case.

                                           -6-
review and publication’; (3) ‘the known or potential rate of error’; and (4) whether
the theory has been generally accepted.” Peitzmeier v. Hennessy Indus., Inc., 97 F.3d
293, 297 (8th Cir. 1996) (citing Daubert, 509 U.S. at 593-94). Daubert’s progeny
provides additional factors such as: whether the expertise was developed for
litigation or naturally flowed from the expert’s research; whether the proposed expert
ruled out other alternative explanations; and whether the proposed expert sufficiently
connected the proposed testimony with the facts of the case. Bogosian v. Mercedes-
Benz of N. Am., Inc., 104 F.3d 472, 479 (1st Cir. 1997) (finding testimony of the
expert and the plaintiff must be sufficiently related); Daubert v. Merrell Dow Pharm.,
Inc., 43 F.3d 1311, 1317 (9th Cir. 1995) (addressing whether opinion was developed
naturally out of research or solely for litigation); Claar v. Burlington N. R. Co., 29
F.3d 499 (9th Cir. 1994) (discussing whether the expert accounts for obvious
alternative explanations).2

      2
        The Eighth Circuit has been consistently loyal to the language of Daubert and
Federal Rule of Evidence 702. Of course, the facts in each situation are sui generis
in that each panel opinion differs upon the varying evidential proofs. However, our
examination of the cases in the Eighth Circuit show a consistent application of
Daubert and Rule 702. We set out a collation of the various cases.

       The cases that admit expert testimony are as follows: Clark v. Heidrick, 150
F.3d 912, 915 (8th Cir. 1998) (finding expert testimony offered by defendant as to
possible causes of baby’s brachial plexus injuries admissible but excluded plaintiff’s
medical expert’s testimony that flexion during delivery was the most likely
explanation for the baby’s injuries on grounds outside of Daubert; it was offered for
the first time in rebuttal and not the case in chief); Jensen v. Eveleth Taconite Co.,
130 F.3d 1287, 1299 (8th Cir. 1997) (admitting testimony of well-qualified
psychiatrists and psychologists on issue of damages for mental anguish and
emphasizing that weight and credibility accorded to the testimony is left to the trier
of fact); United States v. Davis, 103 F.3d 660, 674 (8th Cir. 1996) (finding expert
testimony on ballistics was admissible based upon Daubert factors after a preliminary
evidentiary hearing was held); United States v. Beasley, 102 F.3d 1440, 1447 (8th
Cir. 1996) (allowing PCR method of DNA testing to be admitted due to its reliability,
as demonstrated by applying the Daubert factors); Hose v Chicago Northwestern

                                         -7-
Transp. Co., 70 F.3d 968, 973-76 (8th Cir. 1995) (allowing physician to testify as to
position emission tomography scan of employee’s brain, polysomnogram, and that
employee’s manganese encephalopathy was caused by inhalation of manganese fumes
at employer’s plant after analyzing the testimony in light of Daubert); United States
v. Johnson, 28 F.3d 1487, 1497 (8th Cir. 1994) (allowing a coconspirator and gang
member to testify as an expert regarding drug trafficking, which was found helpful
to the jury, due to his extensive experience in the business of drug trafficking,
evidenced by his six years establishing various drug distribution centers in assorted
cities).

       The cases that limit the proposed expert testimony are as follows: Wheeling
Pittsburgh Steel Corp. v. Beelman River Terminals, Inc., 254 F.3d 706, 715 (8th Cir.
2001) (limiting testimony of an expert hydrologist to flood risk, thereby, finding
testimony as to safe warehousing practices inadmissible); Weisgram v. Marley Co.,
169 F.3d 514, 519 (8th Cir. 1999) (allowing a fire investigator to testify as to the
origins of the fire but not as to the cause of the fire since there was no evidence in
record to substantiate it); Robertson v. Norton Co., 148 F.3d 905, 907 (8th Cir. 1998)
(admitting testimony of expert as to manufacturing defect, but not as to the defect of
the warning label).

       The proposed expert testimony was excluded in the following cases: Glastetter
v. Novartis Phar. Corp., 252 F.3d 986, 992 (8th Cir. 2001) (excluding proposed
expert testimony that Parlodel can cause intracerebral hemorrhages because proposed
expert could not demonstrate causation to a degree of medical certainty as required
by Daubert); Children’s Broad. Corp. v. Walt Disney Co., 245 F.3d 1008, 1018 (8th
Cir. 2001) (excluding the testimony presented by a proposed expert, that any breach
of contract, any use of confidential information, or any misappropriation of any trade
secret caused the exact same amount of damages, because he failed to consider the
effect of competition, theory on causation was questionable and his testimony was
based on a report produced prior to narrowing the claims for trial); J.B. Hunt Transp.,
Inc., v. General Motors Corp., 243 F.3d 441, 444 (8th Cir. 2001) (preventing a
reconstruction expert from testifying because he had insufficient evidence to
completely reconstruct the accident as he theorized and expertise of a “foam expert”
not allowed where testimony is highly doubtful and linked to rejected testimony of
reconstruction expert); Giles v. Miners, Inc., 242 F.3d 810, 812-13 (8th Cir. 2001)
(precluding proposed expert from testifying based upon proposed expert’s failure to

                                         -8-
indicate how proposed safety guard would interact with freezer’s proper functioning
and it appeared the safety guard violated government and industry design standards
requiring sanitary, easily cleanable surface); Turner v. Iowa Fire Equip., 229 F.3d
1202, 1208 (8th Cir. 2000) (preventing a proposed expert from testifying because
differential diagnosis sought to identify the condition and not the cause); Blue Dane
Simmental Corp. v. Am. Simmental Ass’n, 178 F.3d 1035, 1041 (8th Cir. 1999)
(precluding the proposed expert economist from testifying because “no other
economists use before-and-after modeling to support conclusions of causes of market
fluctuation”); Jaurequi v. Carter Mfg. Co., Inc., 173 F.3d 1076, 1084 (8th Cir. 1999)
(excluding proposed expert testimony on alternative design because of failure to
provide basis for belief that opinion was anything more than unabashed speculation);
Penney v. Praxair, Inc., 116 F.3d 330, 333-34 (8th Cir. 1997) (holding proposed
expert testimony based upon comparison of positron emission tomography scan of
brain of plaintiff and control group, which demonstrated traumatic brain injury, was
found inadmissible because control group could not provide accurate comparison due
to differences in age and plaintiff’s use of medication); Wright v. Williamette Inds.,
Inc., 91 F.3d 1105, 1108 (8th Cir. 1996) (holding opinion of proposed expert, that
complaints of residents near manufacturing plant were more probably than not related
to their exposure to formaldehyde from plant, was not based on any knowledge about
what amounts of wood fibers impregnated with formaldehyde involve appreciable
risk of harm to human beings who breathe them, and so district court should have
excluded expert’s testimony); Peitzmeier v. Hennessey Indus., Inc., 97 F.3d 293, 297-
98 (8th Cir. 1996) (excluding testimony of proposed expert because no testing ever
took place, no peer review and no testimony regarding general acceptance was
offered); Pestel v. Vermeer Mfg. Co., 64 F.3d 382, 384 (8th Cir. 1995) (finding that
district court properly found that proposed expert was precluded from testifying about
alternative design in products liability suit because of lack of testing, failed to contact
others in industry to see if they had attempted to create a similar guard, not subjected
concept to any outside scrutiny and not generally accepted); Sorensen v. Shakless
Corp., 31 F.3d 638, 648-51 (8th Cir. 1994) (precluding proposed expert testimony
because it was not relevant due to lack of reliable inference that Shaklee alfalfa
tablets taken by parents contained any EtO, a toxin that can cause birth defects, as
well as a failure to satisfy any of the Daubert factors); Nat’l Bank of Commerce of El
Dorado v. Assoc. Milk Producers, Inc., 22 F. Supp. 2d 942, 963 (E.D. Ark. 1998),
aff’d 191 F.3d 858 (8th Cir. 1999) (finding the proposed expert had not ruled out
possible alternative causes and has failed to rule in the alleged toxin as a contributing

                                           -9-
A. Testing

       The first relevant factor is whether the expert’s theory can be (and has been)
tested. Daubert, 509 U.S. at 593. The district court found Kelsey’s testing was
inadequate because he was unable to duplicate the events of the accident. As a result,
the district court found the testing factor weighed against the admission of Kelsey’s
testimony.

       Kelsey’s initial testing focused on two possible causes of Lauzon’s injury:
manufacturing or design defect. Pictures were taken of the SN2 involved in the
accident. The trigger force was measured as well as the force needed to activate the
bottom contact point. Nail speed was measured from varied distances. A pendulum
test was then attempted in order to measure recoil forces of the SN2.3 The section
of the roof was reproduced and the tasks Lauzon was performing were reenacted and
recorded on video tape.

       During the course of the examination, Kelsey determined this particular SN2
required depression of both the trigger and the bottom contact point to drive nails
under any circumstance. Thus, Kelsey’s testing provided additional trustworthiness
to his opinion, contributed by objectively excluding one of Lauzon’s claims, that the
SN2 had a manufacturing defect.



cause of the cancer).

      The evidentiary foundation determined to be lacking in the Eighth Circuit cases
where the experts’ testimony has been excluded, as we have attempted to analytically
explain, is not missing in the foundational proof in the present case.
      3
      The sticky operation of the contact point precluded commission of the
pendulum test and its findings on recoil forces.

                                        -10-
      Due to previous experience with bottom-fire pneumatic nailers, Kelsey was
aware they had a tendency to double-fire. He noted such in his report when he stated:

      this tool like [other bottom-fire pneumatic nailers] is subject to recoil
      fire as a result of unexpected recoil forces operating back against the
      operator’s grip. Under these circumstances, multiple nail firing does
      occur with some frequency, particularly when the recoil force is not
      correctly anticipated by the user as in the circumstance of the nail hitting
      harder or more dense area in the wood.

H. Boulter Kelsey, Expert Report, at 6. Kelsey’s opinion was also supported by
Lauzon’s employer, Tony Hayes. He testified that this particular SN2 had a history
of double-fires: “I don’t know what you would call it, but if you–if you pushed it
against the wood and pulled the trigger, it would bounce back on you and shoot a
second nail.”

        The information obtained from the tests performed and the factual record were
analyzed by Kelsey in the light of the teachings of mechanical engineering. The
foregoing analysis ruled out a manufacturing defect. Instead of a manufacturing
defect, Kelsey’s testing led to the conclusion of a double-fire, a design defect. Kelsey
testified that designing the SN2 as a sequential-fire pneumatic nailer would have
prevented the accident from occurring because two nails could not be fired without
actuating both the trigger and bottom contact point. Thus, the second nail, according
to the testimony of Lauzon, would not have become impaled in his hand.

       Kelsey has also testified as an expert in numerous other cases involving injuries
resulting from the use of pneumatic air guns. Instead of detracting from reliability,
this fact, coupled with Kelsey’s testing and subsequent analysis in the present case,
provides more than sufficient evidence to find that this factor weighs heavily in favor
of admitting the testimony of Kelsey as an expert witness.



                                         -11-
B. Peer Review and Publication

       Another applicable factor is whether the theory or technique has been subjected
to peer review and publication. Daubert, 509 U.S. at 593. “The fact of publication
(or lack thereof) in a peer reviewed journal thus will be a relevant, though not
dispositive, consideration . . . .” Id. at 594. Rather, the focus remains on reliability.4
Kannankeril v. Terminix Inter., Inc., 128 F.3d 802, 809 (3rd Cir. 1997) (citing
Daubert, 509 U.S. at 593).

       The district court held the peer-reviewed literature involved in this case did not
rise to the level contemplated by Daubert. Therefore, the district court found this
factor weighed against admitting the proffered testimony.

       Kelsey authored an article, which was made an exhibit to his report, about
pneumatic nailers that appeared in the Journal of the National Academy of Forensic
Engineers. H. Boulter Kelsey, Jr., Forensic Engineering Aspects of Nail Gun
Litigation, 25 Journal of the National Academy of Forensic Engineers 1 (1998)
[hereinafter H. Boulter Kelsey]. As exemplified by its title, it is an organization, with
approximately 450 members, whose work is primarily devoted to the investigation of
engineering matters pertaining to legal cases. The article was published prior to the
present litigation and comes to the identical conclusion as proffered in this case:
bottom-fire pneumatic nailers are unreasonably dangerous. Id. at 10. In the article,
Kelsey also concludes that the sequential-fire pneumatic nailer is the most effective
means of negating the hazards associated with the inadvertent firing of the pneumatic
nailer. Id.




      4
       “Publication (which is but one element of peer review) is not a sine qua non
of admissibility; it does not necessarily correlate with reliability . . . .” Daubert, 509
U.S. at 593.

                                          -12-
       In addition to Kelsey’s article, two other publications, which were also
provided as exhibits to his report, discuss pneumatic nail gun injuries. The two
publications are a technical report conducted by the State of Washington and an
article in Fine Homebuilding magazine.

      The Washington report, performed by the State Department of Labor and
Industries, examined the nature of pneumatic nail gun hazards in hopes of uncovering
“methods to control and eliminate those hazards.” Washington State Dept. of Labor
and Industries, Pneumatic Nailer (“Nail Gun”) Injuries in Washington State, 1990-
1998, Tech. Rep. No. 59-1 (1999) [hereinafter Washington State Dept.]. After
surveying injuries sustained from pneumatic nail gun use in Washington State, the
Department made recommendations. The first recommendation is to “[u]se the
sequential trigger until a safe record of use and experience with the tool has been
developed.” Id. at 2. The second recommendation is for manufacturers to work with
users in order to “better balance the speed and productivity of the [bottom-fire
pneumatic nailer] with the accuracy and potential for fewer acute trauma injuries
using the ‘sequential’ mode.” Id.

       The Fine Homebuilding article surveys a construction crew’s use of bottom-fire
and sequential-fire pneumatic nailers of various models. Rick Arnold and Mike
Guertin, Survey of Framing Nailers, Fine Homebuilding, Nov. 1996 [hereinafter Fine
Homebuilding]. The survey directly compares bottom-fire pneumatic nailers and
sequential-fire nailers in the setting they are commonly employed. The survey found
bottom-fire pneumatic nailers “present the most danger of accident.” Id. at 78.
Further, it addressed and refuted the contention that bottom-fire pneumatic nailers
allow for greater productivity in comparison to sequential-fire nailers: “we found we
could keep close pace with a [bottom-fire pneumatic nailer] bounce-nailing . . . .” Id.
at 79. In light of its minimal impact upon productivity and the hazards associated
with the bottom-fire pneumatic nailer, the article recommends the sequential-fire
nailer. Id.

                                         -13-
       Clearly, all these articles, which were exhibits to Kelsey’s expert report, offer
support for Kelsey’s conclusion: the bottom-fire pneumatic nailer is unreasonably
dangerous and a commensurate, safer alternative design, the sequential-fire pneumatic
nailer, exists.

       Further support for Kelsey’s testimony under the peer review factor is found
in the very language of Daubert; some propositions are too new to be published.
Daubert, 509 U.S. at 593. The pneumatic fire nailers “increased popularity in the
1990’s appears to have triggered an increase in injuries due to their use.” Washington
State Dept., at 1. The recent increase in nail gun use and injuries stemming therefrom
accounts for, in part, the lack of wealth of peer reviewed information the district court
sought.

       The article published by Kelsey supporting the very essence of his testimony
as well as recognition of the dangers associated with a bottom-fire pneumatic nailer
and the safer alternative of a sequential-fire nailer in two additional publications is
sufficient to meet the peer review factor under Daubert, especially when coupled with
the only recent onset of pneumatic nail gun injuries. Therefore, the peer review factor
weighs in favor of admitting Kelsey’s proffered expert opinion.

C. General Acceptance

      The next applicable factor is general acceptance.5 “Widespread acceptance can
be an important factor in ruling particular evidence admissible, and ‘a known
technique which has been able to attract only minimal support within the community’
may properly be viewed with skepticism.” Daubert, 509 U.S. at 594 (citation
omitted). Although general acceptance may still be a factor, it must be weighed with


      5
        The parties agree that the third Daubert factor, rate of error, is not applicable
to the facts of this case.

                                          -14-
the Supreme Court’s admonition that “a rigid ‘general acceptance’ requirement would
be at odds with the ‘liberal thrust’ of the Federal Rules and their ‘general approach
of relaxing the traditional barriers to ‘opinion’ testimony.’” Id. at 588-89 (quoting
Beech Aircraft Corp., 488 U.S. at 169 (citing Rules 701 to 705)). See also Weinstein,
Rule 702 of the Federal Rules of Evidence is Sound; It Should Not Be Amended, 138
F.R.D. 631 (1991) (“The Rules were designed to depend primarily upon lawyer-
adversaries and sensible triers of fact to evaluate conflicts.”).

      The district court found that there has been no demonstration that Mr. Kelsey’s
theories are accepted, let alone generally accepted by the relevant scientific
community. Thus, the district court found this factor weighed in favor of precluding
Kelsey from testifying as an expert.

      The general acceptance factor dovetails with the prior factor, peer review.
Bottom-fire pneumatic nailers are known for problems associated with double-fires
throughout the industry as illustrated by the aforementioned articles. See Washington
State Dept.; H. Boulter Kelsey; Fine Homebuilding. In addition, those who utilized
this particular SN2 were cognizant of its tendency to double-fire. Tony Hayes,
Lauzon’s employer, testified that the particular SN2 employed by Lauzon had a
tendency to double-fire. Also, Tony Hayes testified, even if the user was aware of the
problem, it could not be consistently avoided. Clearly, it is generally accepted that
bottom-fire pneumatic nailers have the tendency to double-fire. Further, this
tendency to double-fire can cause the user or a co-worker in the vicinity to be injured
due to the release of an unintended nail. See, e.g., Washington State Dept., at 1.

       The next issue under the rubric of general acceptance is whether there exists
general acceptance of the reasonable alternative design, the sequential-fire pneumatic
nailers, as proposed by Kelsey. The report prepared by the State of Washington
recognizes the hazardous propensities of the bottom-fire pneumatic nailers and
recommends use of sequential-fire pneumatic nailers in their stead. Id. at 1-2; see

                                         -15-
also Fine Homebuilding, at 79 (recommending the use of sequential-fire pneumatic
nailers). Further, the use of a sequential-fire pneumatic nailer does not diminish the
efficiency of the tool in comparison to the bottom-fire pneumatic nailer as discovered
in the survey that appears in Fine Homebuilding. Id. (rejecting the common
perception that a sequential trip mechanism is slower).

      Kelsey’s opinion comports with those generally accepted in the industry in
recognizing the hazards associated with the bottom-fire pneumatic nailer’s propensity
to double-fire as well as a reasonable alternative, the sequential-fire pneumatic nailer.
We conclude the factor of general acceptance weighs substantially in favor of
accepting the proffered testimony of Kelsey.

D. Opinion’s Basis

        The next factor stems from the direct progeny of the Supreme Court’s decision
in Daubert. On remand, the U.S. Court of Appeals for the Ninth Circuit discussed the
importance from where the proffered expert opinion emanates.6 Daubert, 43 F.3d at
1317. “That an expert testifies based on research he has conducted independent of
litigation provides important, objective proof that the research comports with the
dictates of good science.” Id. (citing Peter W. Huber, Galileo’s Revenge: Junk
Science in the Courtroom, 206-09 (1991)). An expert’s finding that flows from
research independent of litigation is less likely to be biased and the expert is limited
to “the degree to which he can tailor his testimony to serve a party’s interests.” Id.

        Kelsey’s introduction into the field of pneumatic fire nailers was through past
litigation. The article he authored arose from this involvement, although additional
testing was performed outside of the litigation. See id. Yet, Kelsey’s opinion in this


      6
       The district court discussed the factor indirectly under peer review and
publication.

                                          -16-
case does not solely originate from this past research, rather, emanates from his own
independent testing. As previously stated under the testing factor, Kelsey performed
the following tests: took pictures of the SN2 in question; measured trigger forces;
measured force to activate the bottom contact point; measured nail speed; attempted
a pendulum test; and recreated and recorded the incident. Thus, Kelsey’s testimony
stems not only from his involvement in past litigation, but also from the testing
performed on the particular SN2 employed by Lauzon.

        Further, the independence of his testimony is demonstrated by its seeming
contradiction with that of Lauzon. Id. Kelsey opines that the bottom contact point
touched the sheathing and a double-fire occurred, but Lauzon contends the bottom
contact point did not hit the sheathing so a double-fire did not occur. This
contradiction foments the conclusion that Kelsey’s testimony flows naturally out of
his own research by illustrating that the plaintiff does not control his testimony. See
id. If the plaintiff dictated Kelsey’s testimony, surely his opinion as to how the injury
occurred would not conflict with the plaintiff’s own testimony.

       Further support for this factor is found by adhering to its underling rationale,
scientific reliability. Id. (citing Peter W. Huber, Galileo’s Revenge: Junk Science
in the Courtroom, 206-09 (1991)). Scientific reliability can also be shown “by proof
that the research and analysis supporting the proffered conclusions have been
subjected to normal scientific scrutiny through peer review and publication.”
Daubert, 43 F.3d at 1318. As demonstrated earlier, the peer review and general
acceptance factors favor admission of Kelsey’s expert opinion.

      In conclusion, the slight negative impact of Kelsey’s introduction to the field
of pneumatic nail guns through litigation is outweighed by his independent research,
independent testimony, and adherence to the underlying rationale of the general
acceptance factor, scientific reliability.



                                          -17-
E.    Exclusion of Possible Causes

      Another factor commonly applied to the determination of admissibility of an
expert opinion is the ability to rule out other possibilities.7 Claar, 29 F.3d at 453
(discussing whether the expert accounts for obvious alternative explanations); cf
Ambrosini v. Labarraque, 101 F.3d 129 (D.C. Cir. 1996) (stating that the existence
of causes not eliminated pertains to weight and not admissibility). Yet, this
requirement cannot be carried to a quixotic extreme. Exemplifying this limitation,
the U.S. Court of Appeals for the Third Circuit concluded that an “‘expert’s causation
conclusion should not be excluded because he or she has failed to rule out every
possible alternative cause.’” Westberry v. Gislaved Gummi AB, 178 F.3d 257, 265
(4th Cir. 1999) (quoting Heller v. Shaw Indus., Inc., 167 F.3d 146, 156 (3rd Cir.
1999)) (emphasis added).




      7
        Courts often cite this factor when addressing an expert opinion on causation
arrived through a differential diagnosis. See, e.g., Turner, 229 F.3d at 1207
(discussing whether the doctor’s differential diagnosis was aimed at cause or solely
symptoms); Glastetter v. Novartis Pharm. Corp., 252 F.3d 986, 989 (8th Cir. 2001)
(detailing doctors’ differential diagnosis in attempting to connect Parlodel and
intracerebral brain hemorrhage); Westberry v. Gislaved Gummi AB, 178 F.3d 257,
262-66 (4th Cir. 1999) (detailing that a doctor’s differential diagnosis is generally
accepted and also discussing the requirement to rule out possible alternatives as well
as rule in the alleged cause); Nat’l Bank of Commerce of El Dorado v. Associated
Milk Producers, Inc., 22 F. Supp. 2d 942, 963 (E.D. Ark. 1998) (stating that even
when a doctor rules out alternatives, the plaintiff still bears the burden of ruling the
claim in). As illustrated, doctors commonly utilize the method. A differential
diagnosis is performed by “‘ruling in’ all scientifically plausible causes of the
plaintiff’s injury. The physician then ‘rules out’ the least plausible causes of injury
until the most likely cause remains.” Glastetter, 252 F.3d at 989 (8th Cir. 2001). The
remaining cause is the expert’s conclusion as to what caused or did not cause the
plaintiff’s injury. Id.

                                         -18-
      The district court did not separately discuss this factor, rather, addressed it
under testing, the first factor. The court found Kelsey was unable to rule out other
accident theories, except for ruling out a manufacturing defect.

       Kelsey’s testing demonstrated the SN2 in question would not fire with only the
trigger mechanism being depressed, rather, both the bottom contact point and trigger
had to be activated. This ruled out a manufacturing defect. Kelsey has ruled out all
other possible explanations through a safer alternative design, the sequential-fire
pneumatic nailer. Kelsey opined that a properly designed tool, a sequential-fire tool,
would prevent an injury under any theory in this case. It is undisputed that Lauzon
continually depressed the trigger as he was securing the roof sheathing. Utilizing a
sequential fire tool would have required the bottom contact point to be depressed
against the roof sheathing and then the trigger to be pulled each time he sought to fire
a nail. Thus, Kelsey’s proffered opinion rules out all possible causes because the use
of the sequential-fire tool would preclude a nail being expelled at all, let alone into
the hand of Lauzon.

       Even a specious interpretation of Kelsey’s testimony, which would enable other
possible theories of the event to exist such as an accident, does not preclude his
testimony under this factor. In Westberry, the court found the doctor only “explained
why he did not believe that the cold Westberry developed in 1994 or the waterskiing
he did over that summer accounted for his sinus problems.” Id. at 266. The doctor’s
explanations as to conclusions not ruled out went to weight and not admissibility. Id.
265-66. After discounting obvious alternatives through scientific testing, such as the
manufacturing defect, Kelsey need only be able to explain why other conceivable
causes are excludable. Senco may attack Kelsey’s explanations of causation on cross
examination, thereby requiring Kelsey to offer valid explanations as to why his
conclusion remains reliable. See McCullock v. H.B. Fuller Co., 61 F.3d at 1038,
1044 (2d Cir. 1995). To hold otherwise denigrates Justice Blackmun’s observation
in Daubert:

                                         -19-
      [I]n this regard respondent seems to us to be overly pessimistic about the
      capabilities of the jury and of the adversary system generally. Vigorous
      cross-examination, presentation of contrary evidence, and careful
      instruction on the burden of proof are the traditional and appropriate
      means of attacking shaky but admissible evidence. See Rock v.
      Arkansas, 483 U.S. 44, 61 (1987).

Daubert, 509 U.S. at 596.

       The ruling out of the manufacturing defect simultaneously rules in a design
defect. Further, an accurate interpretation of Kelsey’s testimony illustrates that he
opines a sequential-fire tool precludes all other theories, including accidental. Even
a specious interpretation allows for the testimony to be admitted because of his
exclusion of other claims and due to the protections afforded by the very nature of our
legal system. In conclusion, sufficient evidence exists to meet this factor.

F. Relevancy

       The last applicable factor that bears upon the admission of expert testimony
under Rule 702 is whether the opinion offered by the expert is sufficiently related to
the facts of the case such that it will aid the jury in resolving the factual dispute. Id.
at 591; see also Bogosian, 104 F.3d at 479 (finding that testimony of expert and that
of plaintiff must be sufficiently related).

       The district court appeared more concerned with this factor than any other.
The trial court held the theory offered by Kelsey does not sufficiently relate to
Lauzon’s recollection of events. Thus, the trial court found that Kelsey’s opinion was
not relevant and weighed against admitting his testimony.

     Differences do exist between Lauzon’s and Kelsey’s versions of the event.
Lauzon testified that he properly drove a nail and, as the SN2 recoiled, two more nails

                                          -20-
were driven. He believes a double-fire did not take place because he thought the
bottom contact point was four to five inches above the sheathing, therefore, the firing
mechanism could not have been actuated.

      Kelsey discredits, in part, Lauzon’s theory of the event based upon his research
and scientific testing. Kelsey tested the SN2 for a manufacturing defect, one that
would enable the SN2 to drive nails when the trigger was pulled, even though the
bottom contact point was not depressed. Through testing, Kelsey was unable to find
such a defect in the particular SN2. As a result of the tests conducted, Kelsey
concluded, “Lauzon’s recollection of the accident occurrence is in error . . . . [I]n the
process of moving his body down the sloped roof surface, Lauzon unintentionally and
unconsciously caused the nose trigger of the [SN2] to contact the edge . . . .”
sheathing, causing a double-fire. H. Boulter Kelsey, Expert Report, at 6.

       Though a simple comparison of the aforementioned testimony reveals what
appears to be two varied versions of the event, a more detailed analysis demonstrates
their symbiotic relationship, especially in light of corroborating testimony. Kelsey
has objectively proven that the supposed manner Lauzon contends the accident
happened was not scientifically possible: the SN2 would not fire without the bottom
contact point and trigger being depressed. Senco concurs in Kelsey’s scientific
conclusion. In spite of the contradiction between Kelsey and Lauzon’s testimony,
Kelsey does not discredit Lauzon’s testimony. Instead, Kelsey explains how
Lauzon’s recollection of the event, specifically that the SN2 was four to five inches
above the sheathing, further evidences the double-fire: since Lauzon did not intend
to drive the nail, he experienced a double-fire due to an unexpected recoil operating
against his hand. Thus, a more detailed examination illustrates that Kelsey’s
testimony is dependent upon Lauzon’s recollection of the event. If Lauzon was aware
that the bottom contact point was depressed, the recoil fire would not have occurred
because the recoil would have been anticipated. As a result, the bottom triggering



                                          -21-
mechanism would not have remained in contact with the sheathing and the tool could
not have cycled again.

       Kelsey’s double-fire conclusion is consistent with other crucial aspects of
Lauzon’s testimony as well as the sole eye-witness, Nelson. Lauzon testified that two
nails were expelled in rapid succession. It was the second nail that imbedded itself
in Lauzon’s hand. This comports with Kelsey’s conclusion that there was a double-
fire. Further credence is given to Kelsey’s version of the event in light of the
statement given by Nelson. Nelson states he clearly remembers the bottom contact
point hitting the edge of the sheathing.8 We would agree that where opinion
testimony has no support in the record that it should be excluded. See Weisgram,
169 F.3d at 518-20. However, in the present case the district court failed to recognize
the connection between Nelson’s statement as the sole eye-witness and the testimony
of Kelsey. In conclusion, Nelson’s recollections and portions of Lauzon’s testimony
clearly correspond with and support Kelsey’s conclusions.

       What is apparent from the foregoing analysis is that a sufficient nexus exists
between the testimony of Lauzon and Nelson and that of Kelsey. Thus, Kelsey’s
proffered expert testimony will aid the jury in their determination. See Daubert, 509
U.S. at 591. It is far better where, in the mind of the district court, there exists a close
case on relevancy of the expert testimony in light of the plaintiff’s testimony to allow
the expert opinion and if the court remains unconvinced, allow the jury to pass on the




       8
        An examination of the nature of the incident could account for the difference
between the testimony offered by Kelsey and Nelson and that of Lauzon. A jury
could readily find that Lauzon’s recollection may have be clouded by the suddenness
of the accident.

                                           -22-
evidence. Depending on the verdict,9 the trial court can always refer to Federal Rule
of Civil Procedure 50(b) and grant a judgment as a matter of law or a new trial.

      In conclusion, we find a sufficient relationship exists between the facts and the
expert testimony proffered by Kelsey to aid the jury in resolving the factual dispute.

II. Conclusion

       Through examination of the record in light of the requirements of Daubert and
its progeny, ineluctably we are led to conclude the district court’s exclusion of the
testimony was an abuse of discretion and fell outside the spirit of admissibility as set
forth in Federal Rule of Evidence 702. We reverse the district court’s exclusion of
Kelsey’s proffered expert testimony and remand the case for further proceedings
consistent with this opinion. We likewise reverse the district court’s grant of
summary judgment.

      REVERSED and REMANDED.

      A true copy.

             Attest:

                 CLERK, U.S. COURT OF APPEALS, EIGHTH CIRCUIT.




      9
       It is important to remember that any discrepancies that do exist affect
credibility and not admissibility. Daubert, 509 U.S. at 591; See also Kannankeril,
128 F.3d at 807-8.

                                         -23-
