Syllabus
NOTE: Where it is feasible, a syllabus (headnote) will be released,
as is being done in connection with this case, at the time the opinion
is issued.
The syllabus constitutes no part of the opinion of the Court but has
been prepared by the Reporter of Decisions for the convenience of the
reader.
See United States v. Detroit Timber & Lumber Co.,
200 U.S. 321, 337.
SUPREME COURT OF THE UNITED STATES
KUMHO TIRE CO., LTD., et al. v. CARMICHAEL
et al.
ON WRIT CERTIORARI TO THE UNITED STATES COURT OF APPEALS
FOR THE ELEVENTH CIRCUIT
No. 97—1709. Argued December 7, 1998–Decided March 23, 1999
When a tire on the vehicle driven by Patrick Carmichael blew out and
the vehicle overturned, one passenger died and the others were injured.
The survivors and the decedent’s representative, respondents here,
brought this diversity suit against the tire’s maker and its distributor
(collectively Kumho Tire), claiming that the tire that failed was
defective. They rested their case in significant part upon the depositions
of a tire failure analyst, Dennis Carlson, Jr., who intended to testify
that, in his expert opinion, a defect in the tire’s manufacture or
design caused the blow out. That opinion was based upon a visual
and tactile inspection of the tire and upon the theory that in the
absence of at least two of four specific, physical symptoms indicating
tire abuse, the tire failure of the sort that occurred here was caused
by a defect. Kumho Tire moved to exclude Carlson’s testimony on the
ground that his methodology failed to satisfy Federal Rule of Evidence
702, which says: “If scientific, technical, or other specialized
knowledge will assist the trier of fact … , a witness qualified as
an expert … may testify thereto in the form of an opinion.” Granting
the motion (and entering summary judgment for the defendants), the
District Court acknowledged that it should act as a reliability “gatekeeper”
under Daubert v. Merrell Dow Pharmaceuticals, Inc., 509
U.S. 579, 589, in which this Court held that Rule 702 imposes a special
obligation upon a trial judge to ensure that scientific testimony
is not only relevant, but reliable. The court noted that Daubert discussed
four factors–testing, peer review, error rates, and “acceptability”
in the relevant scientific community–which might prove helpful in
determining the reliability of a particular scientific theory or
technique, id., at 593—594, and found that those factors
argued against the reliability of Carlson’s methodology. On the plaintiffs’
motion for reconsideration, the court agreed that Daubert should
be applied flexibly, that its four factors were simply illustrative,
and that other factors could argue in favor of admissibility. However,
the court affirmed its earlier order because it found insufficient
indications of the reliability of Carlson’s methodology. In reversing,
the Eleventh Circuit held that the District Court had erred as a
matter of law in applying Daubert. Believing that Daubert was
limited to the scientific context, the court held that the Daubert factors
did not apply to Carlson’s testimony, which it characterized as skill-
or experience-based.
Held:
1. The Daubert factors may apply to the testimony of engineers
and other experts who are not scientists. Pp. 7—13.
(a) The Daubert “gatekeeping” obligation applies not only to
“scientific” testimony, but to all expert testimony. Rule 702 does not
distinguish between “scientific” knowledge and “technical” or “other
specialized” knowledge, but makes clear that any such knowledge might
become the subject of expert testimony. It is the Rule’s word “knowledge,”
not the words (like “scientific”) that modify that word, that establishes
a standard of evidentiary reliability. 509 U.S., at 589—590. Daubert referred
only to “scientific” knowledge because that was the nature of the expertise
there at issue. Id., at 590, n. 8. Neither is the evidentiary
rationale underlying Daubert’s “gatekeeping” determination limited
to “scientific” knowledge. Rules 702 and 703 grant all expert witnesses,
not just “scientific” ones, testimonial latitude unavailable to other
witnesses on the assumption that the expert’s opinion will have a reliable
basis in the knowledge and experience of his discipline. Id., at
592. Finally, it would prove difficult, if not impossible, for judges
to administer evidentiary rules under which a “gatekeeping” obligation
depended upon a distinction between “scientific” knowledge and “technical”
or “other specialized” knowledge, since there is no clear line dividing
the one from the others and no convincing need to make such distinctions.
Pp. 7—9.
(b) A trial judge determining the admissibility of an engineering expert’s
testimony may consider one or more of the specific Daubert factors.
The emphasis on the word “may” reflects Daubert’s description
of the Rule 702 inquiry as “a flexible one.” 509 U.S., at 594. The Daubert factors
do not constitute a definitive checklist or test, id., at
593, and the gatekeeping inquiry must be tied to the particular facts, id., at
591. Those factors may or may not be pertinent in assessing reliability,
depending on the nature of the issue, the expert’s particular expertise,
and the subject of his testimony. Some of those factors may be helpful
in evaluating the reliability even of experience-based expert testimony,
and the Court of Appeals erred insofar as it ruled those factors
out in such cases. In determining whether particular expert testimony
is reliable, the trial court should consider the specific Daubert factors
where they are reasonable measures of reliability. Pp. 10—12.
(c) The court of appeals must apply an abuse-of-discretion standard
when it reviews the trial court’s decision to admit or exclude expert
testimony. General Electric Co. v. Joiner, 522
U.S. 136, 138—139. That standard applies as much to the trial court’s
decisions about how to determine reliability as to its ultimate conclusion.
Thus, whether Daubert’s specific factors are, or are not,
reasonable measures of reliability in a particular case is a matter
that the law grants the trial judge broad latitude to determine.
See id., at 143. The Eleventh Circuit erred insofar as it
held to the contrary. P. 13.
2. Application of the foregoing standards demonstrates that the District
Court’s decision not to admit Carlson’s expert testimony was lawful.
The District Court did not question Carlson’s qualifications, but
excluded his testimony because it initially doubted his methodology
and then found it unreliable after examining the transcript in some
detail and considering respondents’ defense of it. The doubts that
triggered the court’s initial inquiry were reasonable, as was the
court’s ultimate conclusion that Carlson could not reliably determine
the cause of the failure of the tire in question. The question was
not the reliability of Carlson’s methodology in general, but rather
whether he could reliably determine the cause of failure of the
particular tire at issue. That tire, Carlson conceded, had traveled
far enough so that some of the tread had been worn bald, it should
have been taken out of service, it had been repaired (inadequately)
for punctures, and it bore some of the very marks that he said indicated,
not a defect, but abuse. Moreover, Carlson’s own testimony cast considerable
doubt upon the reliability of both his theory about the need for
at least two signs of abuse and his proposition about the significance
of visual inspection in this case. Respondents stress that other
tire failure experts, like Carlson, rely on visual and tactile examinations
of tires. But there is no indication in the record that other experts
in the industry use Carlson’s particular approach or that
tire experts normally make the very fine distinctions necessary to
support his conclusions, nor are there references to articles or
papers that validate his approach. Respondents’ argument that the
District Court too rigidly applied Daubert might have had
some validity with respect to the court’s initial opinion, but fails
because the court, on reconsideration, recognized that the relevant
reliability inquiry should be “flexible,” and ultimately based its
decision upon Carlson’s failure to satisfy either Daubert’s
factors or any other set of reasonable reliability criteria.
Pp. 13—19.
131 F.3d 1433, reversed.
Breyer, J., delivered the opinion of the Court, in which Rehnquist, C. J.,
and O’Connor, Scalia, Kennedy, Souter, Thomas, and Ginsburg, JJ.,
joined, and in which Stevens, J., joined as to Parts I and II. Scalia,
J., filed a concurring opinion, in which O’Connor and Thomas, JJ.,
joined. Stevens, J., filed an opinion concurring in part and dissenting
in part.
Opinion of the Court
NOTICE: This opinion is subject to formal revision before publication
in the preliminary print of the United States Reports. Readers are
requested to notify the Reporter of Decisions, Supreme Court of the
United States, Washington, D. C. 20543, of any typographical or other
formal errors, in order that corrections may be made before the preliminary
print goes to press.
[March 23, 1999]
Justice Breyer delivered the opinion of the Court.
In Daubert v. Merrell Dow Pharmaceuticals, Inc., 509
U.S. 579 (1993), this Court focused upon the admissibility of scientific
expert testimony. It pointed out that such testimony is admissible only
if it is both relevant and reliable. And it held that the Federal Rules
of Evidence “assign to the trial judge the task of ensuring that an expert’s
testimony both rests on a reliable foundation and is relevant to the
task at hand.” Id., at 597. The Court also discussed certain
more specific factors, such as testing, peer review, error rates, and
“acceptability” in the relevant scientific community, some or all of
which might prove helpful in determining the reliability of a particular
scientific “theory or technique.” Id., at 593—594.
This case requires us to decide how Daubert applies to the testimony
of engineers and other experts who are not scientists. We conclude that Daubert’s
general holding– setting forth the trial judge’s general “gatekeeping”
obligation–applies not only to testimony based on “scientific” knowledge,
but also to testimony based on “technical” and “other specialized” knowledge.
See Fed. Rule Evid. 702. We also conclude that a trial court may consider
one or more of the more specific factors that Daubert mentioned
when doing so will help determine that testimony’s reliability. But,
as the Court stated in Daubert, the test of reliability is “flexible,”
and Daubert’s list of specific factors neither necessarily nor
exclusively applies to all experts or in every case. Rather, the law
grants a district court the same broad latitude when it decides how to
determine reliability as it enjoys in respect to its ultimate reliability
determination. See General Electric Co. v. Joiner, 522
U.S. 136, 143 (1997) (courts of appeals are to apply “abuse of discretion”
standard when reviewing district court’s reliability determination).
Applying these standards, we determine that the District Court’s decision
in this case–not to admit certain expert testimony–was within its discretion
and therefore lawful.
I
On July 6, 1993, the right rear tire of a minivan driven by Patrick Carmichael
blew out. In the accident that followed, one of the passengers died,
and others were severely injured. In October 1993, the Carmichaels
brought this diversity suit against the tire’s maker and its distributor,
whom we refer to collectively as Kumho Tire, claiming that the tire
was defective. The plaintiffs rested their case in significant part
upon deposition testimony provided by an expert in tire failure analysis,
Dennis Carlson, Jr., who intended to testify in support of their
conclusion.
Carlson’s depositions relied upon certain features of tire technology
that are not in dispute. A steel-belted radial tire like the Carmichaels’
is made up of a “carcass” containing many layers of flexible cords,
called “plies,” along which (between the cords and the outer tread)
are laid steel strips called “belts.” Steel wire loops, called “beads,”
hold the cords together at the plies’ bottom edges. An outer layer,
called the “tread,” encases the carcass, and the entire tire is bound
together in rubber, through the application of heat and various chemicals.
See generally, e.g., J. Dixon, Tires, Suspension and Handling
68—72 (2d ed. 1996). The bead of the tire sits upon a “bead seat,”
which is part of the wheel assembly. That assembly contains a “rim
flange,” which extends over the bead and rests against the side of
the tire. See M. Mavrigian, Performance Wheels & Tires 81, 83
(1998) (illustrations).
A. Markovich, How To Buy and Care For Tires 4 (1994).
Carlson’s testimony also accepted certain background facts about the
tire in question. He assumed that before the blowout the tire had
traveled far. (The tire was made in 1988 and had been installed some
time before the Carmichaels bought the used minivan in March 1993;
the Carmichaels had driven the van approximately 7,000 additional
miles in the two months they had owned it.) Carlson noted that the
tire’s tread depth, which was 11/32 of an inch when new, App. 242,
had been worn down to depths that ranged from 3/32 of an inch along
some parts of the tire, to nothing at all along others. Id., at
287. He conceded that the tire tread had at least two punctures which
had been inadequately repaired. Id., at 258—261, 322.
Despite the tire’s age and history, Carlson concluded that a defect in
its manufacture or design caused the blow-out. He rested this conclusion
in part upon three premises which, for present purposes, we must
assume are not in dispute: First, a tire’s carcass should stay bound
to the inner side of the tread for a significant period of time after
its tread depth has worn away. Id., at 208—209. Second,
the tread of the tire at issue had separated from its inner steel-belted
carcass prior to the accident. Id., at 336. Third, this
“separation” caused the blowout. Ibid.
Carlson’s conclusion that a defect caused the separation, however, rested
upon certain other propositions, several of which the defendants
strongly dispute. First, Carlson said that if a separation is not caused
by a certain kind of tire misuse called “overdeflection” (which consists
of underinflating the tire or causing it to carry too much weight,
thereby generating heat that can undo the chemical tread/carcass
bond), then, ordinarily, its cause is a tire defect. Id., at
193—195, 277—278. Second, he said that if a tire has been subject
to sufficient overdeflection to cause a separation, it should reveal
certain physical symptoms. These symptoms include (a) tread wear
on the tire’s shoulder that is greater than the tread wear along
the tire’s center, id., at 211; (b) signs of a “bead groove,”
where the beads have been pushed too hard against the bead seat on
the inside of the tire’s rim, id., at 196—197; (c) sidewalls
of the tire with physical signs of deterioration, such as discoloration, id., at
212; and/or (d) marks on the tire’s rim flange, id., at
219—220. Third, Carlson said that where he does not find at least
two of the four physical signs just mentioned (and presumably
where there is no reason to suspect a less common cause of separation),
he concludes that a manufacturing or design defect caused the separation. Id., at
223—224.
Carlson added that he had inspected the tire in question. He conceded
that the tire to a limited degree showed greater wear on the shoulder
than in the center, some signs of “bead groove,” some discoloration,
a few marks on the rim flange, and inadequately filled puncture holes
(which can also cause heat that might lead to separation). Id., at
256—257, 258—261, 277, 303—304, 308. But, in each instance, he testified
that the symptoms were not significant, and he explained why he believed
that they did not reveal overdeflection. For example, the extra shoulder
wear, he said, appeared primarily on one shoulder, whereas an overdeflected
tire would reveal equally abnormal wear on both shoulders. Id., at
277. Carlson concluded that the tire did not bear at least two of
the four overdeflection symptoms, nor was there any less obvious
cause of separation; and since neither overdeflection nor the punctures
caused the blowout, a defect must have done so.
Kumho Tire moved the District Court to exclude Carlson’s testimony on
the ground that his methodology failed Rule 702’s reliability requirement.
The court agreed with Kumho that it should act as a Daubert-type
reliability “gatekeeper,” even though one might consider Carlson’s
testimony as “technical,” rather than “scientific.” See Carmichael v. Samyang
Tires, Inc., 923 F. Supp. 1514, 1521—1522 (SD Ala. 1996). The
court then examined Carlson’s methodology in light of the reliability-related
factors that Daubert mentioned, such as a theory’s testability,
whether it “has been a subject of peer review or publication,” the
“known or potential rate of error,” and the “degree of acceptance
… within the relevant scientific community.” 923 F. Supp., at 1520
(citing Daubert, 509 U.S., at 592—594). The District Court
found that all those factors argued against the reliability of Carlson’s
methods, and it granted the motion to exclude the testimony (as well
as the defendants’ accompanying motion for summary judgment).
The plaintiffs, arguing that the court’s application of the Daubert factors
was too “inflexible,” asked for reconsideration. And the Court granted
that motion. Carmichael v. Samyang Tires, Inc., Civ.
Action No. 93—0860—CB—S (SD Ala., June 5, 1996), App. to Pet. for Cert.
1c. After reconsidering the matter, the court agreed with the plaintiffs
that Daubert should be applied flexibly, that its four factors
were simply illustrative, and that other factors could argue in favor
of admissibility. It conceded that there may be widespread acceptance
of a “visual-inspection method” for some relevant purposes. But the court
found insufficient indications of the reliability of
“the component of Carlson’s tire failure analysis which most concerned
the Court, namely, the methodology employed by the expert in analyzing
the data obtained in the visual inspection, and the scientific basis,
if any, for such an analysis.” Id., at 6c.
It consequently affirmed its earlier order declaring Carlson’s testimony
inadmissable and granting the defendants’ motion for summary judgment.
The Eleventh Circuit reversed. See Carmichael v. Samyang
Tire, Inc., 131 F.3d 1433 (1997). It “review[ed] … de novo”
the “district court’s legal decision to apply Daubert.” Id., at
1435. It noted that “the Supreme Court in Daubert explicitly
limited its holding to cover only the ‘scientific context,’ ” adding
that “a Daubert analysis” applies only where an expert relies
“on the application of scientific principles,” rather than “on skill-
or experience-based observation.” Id., at 1435—1436. It concluded
that Carlson’s testimony, which it viewed as relying on experience, “falls
outside the scope of Daubert,” that “the district court erred
as a matter of law by applying Daubert in this case,” and that
the case must be remanded for further (non-Daubert-type) consideration
under Rule 702. Id., at 1436.
Kumho Tire petitioned for certiorari, asking us to determine whether
a trial court “may” consider Daubert’s specific “factors”
when determining the “admissibility of an engineering expert’s testimony.”
Pet. for Cert. i. We granted certiorari in light of uncertainty among
the lower courts about whether, or how, Daubert applies
to expert testimony that might be characterized as based not upon
“scientific” knowledge, but rather upon “technical” or “other specialized”
knowledge. Fed. Rule Evid. 702; compare, e.g., Watkins v. Telsmith,
Inc., 121 F.3d 984, 990—991 (CA5 1997), with, e.g., Compton v. Subaru
of America, Inc., 82 F.3d 1513, 1518—1519 (CA10), cert. denied,
519 U.S. 1042 (1996).
II
A
In Daubert, this Court held that Federal Rule of Evidence 702
imposes a special obligation upon a trial judge to “ensure that any and
all scientific testimony … is not only relevant, but reliable.” 509 U.S.,
at 589. The initial question before us is whether this basic gatekeeping
obligation applies only to “scientific” testimony or to all expert testimony.
We, like the parties, believe that it applies to all expert testimony.
See Brief for Petitioners 19; Brief for Respondents 17.
For one thing, Rule 702 itself says:
“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.”
This language makes no relevant distinction between “scientific” knowledge
and “technical” or “other specialized” knowledge. It makes clear
that any such knowledge might become the subject of expert testimony.
In Daubert, the Court specified that it is the Rule’s word
“knowledge,” not the words (like “scientific”) that modify that word,
that “establishes a standard of evidentiary reliability.” 509 U.S.,
at 589—590. Hence, as a matter of language, the Rule applies its
reliability standard to all “scientific,” “technical,” or “other
specialized” matters within its scope. We concede that the Court
in Daubert referred only to “scientific” knowledge. But
as the Court there said, it referred to “scientific” testimony “because
that [wa]s the nature of the expertise” at issue. Id., at
590, n. 8.
Neither is the evidentiary rationale that underlay the Court’s basic Daubert “gatekeeping”
determination limited to “scientific” knowledge. Daubert pointed
out that Federal Rules 702 and 703 grant expert witnesses testimonial
latitude unavailable to other witnesses on the “assumption that the expert’s
opinion will have a reliable basis in the knowledge and experience of
his discipline.” Id., at 592 (pointing out that experts may
testify to opinions, including those that are not based on firsthand
knowledge or observation). The Rules grant that latitude to all experts,
not just to “scientific” ones.
Finally, it would prove difficult, if not impossible, for judges to administer
evidentiary rules under which a gatekeeping obligation depended upon
a distinction between “scientific” knowledge and “technical” or “other
specialized” knowledge. There is no clear line that divides the one
from the others. Disciplines such as engineering rest upon scientific
knowledge. Pure scientific theory itself may depend for its development
upon observation and properly engineered machinery. And conceptual
efforts to distinguish the two are unlikely to produce clear legal
lines capable of application in particular cases. Cf. Brief for National
Academy of Engineering as Amicus Curiae 9 (scientist seeks
to understand nature while the engineer seeks nature’s modification);
Brief for Rubber Manufacturers Association as Amicus Curiae 14—16
(engineering, as an “applied science,” relies on “scientific reasoning
and methodology”); Brief for John Allen et al. as Amici Curiae 6
(engineering relies upon “scientific knowledge and methods”).
Neither is there a convincing need to make such distinctions. Experts
of all kinds tie observations to conclusions through the use of what
Judge Learned Hand called “general truths derived from … specialized
experience.” Hand, Historical and Practical Considerations Regarding
Expert Testimony, 15 Harv. L. Rev. 40, 54 (1901). And whether the
specific expert testimony focuses upon specialized observations,
the specialized translation of those observations into theory, a
specialized theory itself, or the application of such a theory in
a particular case, the expert’s testimony often will rest “upon an
experience confessedly foreign in kind to [the jury’s] own.” Ibid. The
trial judge’s effort to assure that the specialized testimony is
reliable and relevant can help the jury evaluate that foreign experience,
whether the testimony reflects scientific, technical, or other specialized
knowledge.
We conclude that Daubert’s general principles apply to the expert
matters described in Rule 702. The Rule, in respect to all such matters,
“establishes a standard of evidentiary reliability.” 509 U.S., at 590.
It “requires a valid … connection to the pertinent inquiry as a precondition
to admissibility.” Id., at 592. And where such testimony’s factual
basis, data, principles, methods, or their application are called sufficiently
into question, see Part III, infra, the trial judge must determine
whether the testimony has “a reliable basis in the knowledge and experience
of [the relevant] discipline.” 509 U.S., at 592.
B
The petitioners ask more specifically whether a trial judge determining
the “admissibility of an engineering expert’s testimony” may consider
several more specific factors that Daubert said might “bear
on” a judge’s gate-keeping determination. These factors include:
–Whether a “theory or technique … can be (and has been) tested”;
–Whether it “has been subjected to peer review and publication”;
–Whether, in respect to a particular technique, there is a high “known
or potential rate of error” and whether there are “standards controlling
the technique’s operation”; and
–Whether the theory or technique enjoys “general acceptance” within a
“relevant scientific community.” 509 U.S., at 592—594.
Emphasizing the word “may” in the question, we answer that question yes.
Engineering testimony rests upon scientific foundations, the reliability
of which will be at issue in some cases. See, e.g., Brief
for Stephen Bobo et al. as Amici Curiae 23 (stressing the
scientific bases of engineering disciplines). In other cases, the
relevant reliability concerns may focus upon personal knowledge or
experience. As the Solicitor General points out, there are many different
kinds of experts, and many different kinds of expertise. See Brief
for United States as Amicus Curiae 18—19, and n. 5 (citing
cases involving experts in drug terms, handwriting analysis, criminal modus
operandi, land valuation, agricultural practices, railroad procedures,
attorney’s fee valuation, and others). Our emphasis on the word “may”
thus reflects Daubert’s description of the Rule 702 inquiry
as “a flexible one.” 509 U.S., at 594. Daubert makes clear
that the factors it mentions do not constitute a “definitive
checklist or test.” Id., at 593. And Daubert adds
that the gatekeeping inquiry must be “ ‘tied to the facts’ ” of a
particular “case.” Id., at 591 (quoting United States v. Downing,
753 F.2d 1224, 1242 (CA3 1985)). We agree with the Solicitor General
that “[t]he factors identified in Daubert may or may not
be pertinent in assessing reliability, depending on the nature of
the issue, the expert’s particular expertise, and the subject of
his testimony.” Brief for United States as Amicus Curiae 19.
The conclusion, in our view, is that we can neither rule out, nor
rule in, for all cases and for all time the applicability of the
factors mentioned in Daubert, nor can we now do so for subsets
of cases categorized by category of expert or by kind of evidence.
Too much depends upon the particular circumstances of the particular
case at issue.
Daubert itself is not to the contrary. It made clear that its
list of factors was meant to be helpful, not definitive. Indeed, those
factors do not all necessarily apply even in every instance in which
the reliability of scientific testimony is challenged. It might not be
surprising in a particular case, for example, that a claim made by a
scientific witness has never been the subject of peer review, for the
particular application at issue may never previously have interested
any scientist. Nor, on the other hand, does the presence of Daubert’s
general acceptance factor help show that an expert’s testimony is reliable
where the discipline itself lacks reliability, as, for example, do theories
grounded in any so-called generally accepted principles of astrology
or necromancy.
At the same time, and contrary to the Court of Appeals’ view, some of Daubert’s
questions can help to evaluate the reliability even of experience-based
testimony. In certain cases, it will be appropriate for the trial judge
to ask, for example, how often an engineering expert’s experience-based
methodology has produced erroneous results, or whether such a method
is generally accepted in the relevant engineering community. Likewise,
it will at times be useful to ask even of a witness whose expertise is
based purely on experience, say, a perfume tester able to distinguish
among 140 odors at a sniff, whether his preparation is of a kind that
others in the field would recognize as acceptable.
We must therefore disagree with the Eleventh Circuit’s holding that a
trial judge may ask questions of the sort Daubert mentioned
only where an expert “relies on the application of scientific principles,”
but not where an expert relies “on skill- or experience-based observation.”
131 F.3d, at 1435. We do not believe that Rule 702 creates a schematism
that segregates expertise by type while mapping certain kinds of
questions to certain kinds of experts. Life and the legal cases that
it generates are too complex to warrant so definitive a match.
To say this is not to deny the importance of Daubert’s gatekeeping
requirement. The objective of that requirement is to ensure the reliability
and relevancy of expert testimony. It is to make certain that an expert,
whether basing testimony upon professional studies or personal experience,
employs in the courtroom the same level of intellectual rigor that characterizes
the practice of an expert in the relevant field. Nor do we deny that,
as stated in Daubert, the particular questions that it mentioned
will often be appropriate for use in determining the reliability of challenged
expert testimony. Rather, we conclude that the trial judge must have
considerable leeway in deciding in a particular case how to go about
determining whether particular expert testimony is reliable. That is
to say, a trial court should consider the specific factors identified
in Daubert where they are reasonable measures of the reliability
of expert testimony.
C
The trial court must have the same kind of latitude in deciding how to
test an expert’s reliability, and to decide whether or when special briefing
or other proceedings are needed to investigate reliability, as it enjoys
when it decides whether that expert’s relevant testimony is
reliable. Our opinion in Joiner makes clear that a court of
appeals is to apply an abuse-of-discretion standard when it “review[s]
a trial court’s decision to admit or exclude expert testimony.” 522 U.S.,
at 138—139. That standard applies as much to the trial court’s decisions
about how to determine reliability as to its ultimate conclusion. Otherwise,
the trial judge would lack the discretionary authority needed both to
avoid unnecessary “reliability” proceedings in ordinary cases where the
reliability of an expert’s methods is properly taken for granted, and
to require appropriate proceedings in the less usual or more complex
cases where cause for questioning the expert’s reliability arises. Indeed,
the Rules seek to avoid “unjustifiable expense and delay” as part of
their search for “truth” and the “jus[t] determin[ation]” of proceedings.
Fed. Rule Evid. 102. Thus, whether Daubert’s specific factors
are, or are not, reasonable measures of reliability in a particular case
is a matter that the law grants the trial judge broad latitude to determine.
See Joiner, supra, at 143. And the Eleventh Circuit
erred insofar as it held to the contrary.
III
We further explain the way in which a trial judge “may” consider Daubert’s
factors by applying these considerations to the case at hand, a matter
that has been briefed exhaustively by the parties and their 19 amici.
The District Court did not doubt Carlson’s qualifications, which included
a masters degree in mechanical engineering, 10 years’ work at Michelin
America, Inc., and testimony as a tire failure consultant in other tort
cases. Rather, it excluded the testimony because, despite those qualifications,
it initially doubted, and then found unreliable, “the methodology employed
by the expert in analyzing the data obtained in the visual inspection,
and the scientific basis, if any, for such an analysis.” Civ. Action
No. 93—0860—CB—S (SD Ala., June 5, 1996), App. to Pet. for Cert. 6c.
After examining the transcript in “some detail,” 923 F. Supp., at 1518—519,
n. 4, and after considering respondents’ defense of Carlson’s methodology,
the District Court determined that Carlson’s testimony was not reliable.
It fell outside the range where experts might reasonably differ, and
where the jury must decide among the conflicting views of different experts,
even though the evidence is “shaky.” Daubert, 509 U.S., at 596.
In our view, the doubts that triggered the District Court’s initial inquiry
here were reasonable, as was the court’s ultimate conclusion. For one
thing, and contrary to respondents’ suggestion, the specific issue before
the court was not the reasonableness in general of a tire expert’s
use of a visual and tactile inspection to determine whether overdeflection
had caused the tire’s tread to separate from its steel-belted carcass.
Rather, it was the reasonableness of using such an approach, along with
Carlson’s particular method of analyzing the data thereby obtained, to
draw a conclusion regarding the particular matter to which the expert
testimony was directly relevant. That matter concerned the likelihood
that a defect in the tire at issue caused its tread to separate from
its carcass. The tire in question, the expert conceded, had traveled
far enough so that some of the tread had been worn bald; it should have
been taken out of service; it had been repaired (inadequately) for punctures;
and it bore some of the very marks that the expert said indicated, not
a defect, but abuse through overdeflection. See supra, at 3—5;
App. 293—294. The relevant issue was whether the expert could reliably
determine the cause of this tire’s separation. Nor was the basis
for Carlson’s conclusion simply the general theory that, in the absence
of evidence of abuse, a defect will normally have caused a tire’s separation.
Rather, the expert employed a more specific theory to establish the existence
(or absence) of such abuse. Carlson testified precisely that in the absence
of at least two of four signs of abuse (proportionately greater
tread wear on the shoulder; signs of grooves caused by the beads; discolored
sidewalls; marks on the rim flange) he concludes that a defect caused
the separation. And his analysis depended upon acceptance of a further
implicit proposition, namely, that his visual and tactile inspection
could determine that the tire before him had not been abused despite
some evidence of the presence of the very signs for which he looked (and
two punctures).
For another thing, the transcripts of Carlson’s depositions support both
the trial court’s initial uncertainty and its final conclusion. Those
transcripts cast considerable doubt upon the reliability of both
the explicit theory (about the need for two signs of abuse) and the
implicit proposition (about the significance of visual inspection
in this case). Among other things, the expert could not say whether
the tire had traveled more than 10, or 20, or 30, or 40, or 50 thousand
miles, adding that 6,000 miles was “about how far” he could “say
with any certainty.” Id., at 265. The court could reasonably
have wondered about the reliability of a method of visual and tactile
inspection sufficiently precise to ascertain with some certainty
the abuse-related significance of minute shoulder/center relative
tread wear differences, but insufficiently precise to tell “with
any certainty” from the tread wear whether a tire had traveled less
than 10,000 or more than 50,000 miles. And these concerns might have
been augmented by Carlson’s repeated reliance on the “subjective[ness]”
of his mode of analysis in response to questions seeking specific
information regarding how he could differentiate between a tire that
actually had been overdeflected and a tire that merely looked as
though it had been. Id., at 222, 224—225, 285—286. They
would have been further augmented by the fact that Carlson said he
had inspected the tire itself for the first time the morning of his
first deposition, and then only for a few hours. (His initial conclusions
were based on photographs.) Id., at 180.
Moreover, prior to his first deposition, Carlson had issued a signed
report in which he concluded that the tire had “not been … overloaded
or underinflated,” not because of the absence of “two of four” signs
of abuse, but simply because “the rim flange impressions . . . were
normal.” Id., at 335—336. That report also said that the
“tread depth remaining was 3/32 inch,” id., at 336, though
the opposing expert’s (apparently undisputed) measurements indicate
that the tread depth taken at various positions around the tire actually
ranged from .5/32 of an inch to 4/32 of an inch, with the tire apparently
showing greater wear along both shoulders than along the
center, id., at 432—433.
Further, in respect to one sign of abuse, bead grooving, the expert seemed
to deny the sufficiency of his own simple visual-inspection methodology.
He testified that most tires have some bead groove pattern, that
where there is reason to suspect an abnormal bead groove he would
ideally “look at a lot of [similar] tires” to know the grooving’s
significance, and that he had not looked at many tires similar to
the one at issue. Id., at 212—213, 214, 217.
Finally, the court, after looking for a defense of Carlson’s methodology
as applied in these circumstances, found no convincing defense. Rather,
it found (1) that “none” of the Daubert factors, including
that of “general acceptance” in the relevant expert community, indicated
that Carlson’s testimony was reliable, 923 F. Supp., at 1521; (2)
that its own analysis “revealed no countervailing factors operating
in favor of admissibility which could outweigh those identified in Daubert,”
App. to Pet. for Cert. 4c; and (3) that the “parties identified no
such factors in their briefs,” ibid. For these three reasons taken
together, it concluded that Carlson’s testimony was unreliable.
Respondents now argue to us, as they did to the District Court, that
a method of tire failure analysis that employs a visual/tactile inspection
is a reliable method, and they point both to its use by other experts
and to Carlson’s long experience working for Michelin as sufficient
indication that that is so. But no one denies that an expert might
draw a conclusion from a set of observations based on extensive and
specialized experience. Nor does anyone deny that, as a general matter,
tire abuse may often be identified by qualified experts through visual
or tactile inspection of the tire. See Affidavit of H. R. Baumgardner
1—2, cited in Brief for National Academy of Forensic Engineers as Amici
Curiae 16 (Tire engineers rely on visual examination and process
of elimination to analyze experimental test tires). As we said before, supra, at
14, the question before the trial court was specific, not general.
The trial court had to decide whether this particular expert had
sufficient specialized knowledge to assist the jurors “in deciding
the particular issues in the case.” 4 J. McLaughlin, Weinstein’s
Federal Evidence ¶702.05[1], p. 702—33 (2d ed. 1998); see also Advisory
Committee’s Note on Proposed Fed. Rule Evid. 702, Preliminary Draft
of Proposed Amendments to the Federal Rules of Civil Procedure and
Evidence: Request for Comment 126 (1998) (stressing that district
courts must “scrutinize” whether the “principles and methods” employed
by an expert “have been properly applied to the facts of the case”).
The particular issue in this case concerned the use of Carlson’s two-factor
test and his related use of visual/tactile inspection to draw conclusions
on the basis of what seemed small observational differences. We have
found no indication in the record that other experts in the industry
use Carlson’s two-factor test or that tire experts such as Carlson
normally make the very fine distinctions about, say, the symmetry
of comparatively greater shoulder tread wear that were necessary,
on Carlson’s own theory, to support his conclusions. Nor, despite
the prevalence of tire testing, does anyone refer to any articles
or papers that validate Carlson’s approach. Compare Bobo, Tire Flaws
and Separations, in Mechanics of Pneumatic Tires 636—637 (S. Clark
ed. 1981); C. Schnuth et al., Compression Grooving and Rim Flange
Abrasion as Indicators of Over-Deflected Operating Conditions in
Tires, presented to Rubber Division of the American Chemical Society,
Oct. 21—24, 1997; J. Walter & R. Kiminecz, Bead Contact Pressure
Measurements at the Tire-Rim Interface, presented to Society of Automotive
Engineers, Feb. 24—28, 1975. Indeed, no one has argued that Carlson
himself, were he still working for Michelin, would have concluded
in a report to his employer that a similar tire was similarly defective
on grounds identical to those upon which he rested his conclusion
here. Of course, Carlson himself claimed that his method was accurate,
but, as we pointed out in Joiner, “nothing 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.” 522 U.S., at 146.
Respondents additionally argue that the District Court too rigidly applied Daubert’s
criteria. They read its opinion to hold that a failure to satisfy any
one of those criteria automatically renders expert testimony inadmissible.
The District Court’s initial opinion might have been vulnerable to a
form of this argument. There, the court, after rejecting respondents’
claim that Carlson’s testimony was “exempted from Daubert-style
scrutiny” because it was “technical analysis” rather than “scientific
evidence,” simply added that “none of the four admissibility criteria
outlined by the Daubert court are satisfied.” 923 F. Supp.,
at 1522. Subsequently, however, the court granted respondents’ motion
for reconsideration. It then explicitly recognized that the relevant
reliability inquiry “should be ‘flexible,’ ” that its “ ‘overarching
subject [should be] … validity’ and reliability,” and that “Daubert was
intended neither to be exhaustive nor to apply in every case.” App. to
Pet. for Cert. 4c (quoting Daubert, 509 U.S., at 594—595). And
the court ultimately based its decision upon Carlson’s failure to satisfy
either Daubert’s factors or any other set of reasonable
reliability criteria. In light of the record as developed by the parties,
that conclusion was within the District Court’s lawful discretion.
In sum, Rule 702 grants the district judge the discretionary authority,
reviewable for its abuse, to determine reliability in light of the
particular facts and circumstances of the particular case. The District
Court did not abuse its discretionary authority in this case. Hence,
the judgment of the Court of Appeals is
Reversed.
Scalia, J., concurring
[March 23, 1999]
Justice Scalia, with whom Justice O’Connor and Justice Thomas join, concurring.
I join the opinion of the Court, which makes clear that the discretion
it endorses–trial-court discretion in choosing the manner of testing
expert reliability–is not discretion to abandon the gatekeeping function.
I think it worth adding that it is not discretion to perform the
function inadequately. Rather, it is discretion to choose among reasonable means
of excluding expertise that is fausse and science that is
junky. Though, as the Court makes clear today, the Daubert factors
are not holy writ, in a particular case the failure to apply one
or another of them may be unreasonable, and hence an abuse of discretion.
Stevens, J., dissenting
[March 23, 1999]
Justice Stevens, concurring in part and dissenting in part.
The only question that we granted certiorari to decide is whether a trial
judge “[m]ay . . . consider the four factors set out by this Court
in Daubert v. Merrill Dow Pharmaceuticals, Inc., 509
U.S. 579 (1993), in a Rule 702 analysis of admissibility of an engineering
expert’s testimony.” Pet. for Cert. i. That question is fully and
correctly answered in Parts I and II of the Court’s opinion, which
I join.
Part III answers the quite different question whether the trial judge
abused his discretion when he excluded the testimony of Dennis Carlson.
Because a proper answer to that question requires a study of the
record that can be performed more efficiently by the Court of Appeals
than by the nine Members of this Court, I would remand the case to
the Eleventh Circuit to perform that task. There are, of course,
exceptions to most rules, but I firmly believe that it is neither
fair to litigants nor good practice for this Court to reach out to
decide questions not raised by the certiorari petition. See General
Electric Co. v. Joiner, 522 U.S. 136, 150—151 (1997)
(Stevens, J., concurring in part and dissenting in part).
Accordingly, while I do not feel qualified to disagree with the well-reasoned
factual analysis in Part III of the Court’s opinion, I do not join
that Part, and I respectfully dissent from the Court’s disposition
of the case.
