- 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).