OPINION
delivered the opinion of the court,
We granted appeal in this products liability action to determine whether the trial court erred in excluding as unreliable the testimony of the plaintiffs’ two expert witnesses, a mechanical engineer and a biomechanical engineer, and thereafter granting a directed verdict in favor of the defendant. We hold that the trial court erred in applying the nonexclusive list of reliability factors set out in
McDaniel v. CSX Transportation, Inc.,
*273 Charles Brown (“Mr. Brown”) and Barbara Sue Reynolds (“Mrs. Reynolds”) sustained injuries to their left legs while operating two different models of stand-up forklifts manufactured by Crown Equipment Corporation (“Crown”). Mr. Brown and Mrs. Reynolds brought product liability claims against Crown alleging that their injuries were caused by the defective nature of the forklifts. Mrs. Reynolds’ husband, Howard Reynolds (“Mr. Reynolds”), sought compensation from Crown based upon loss of consortium.
Prior to trial, Mr. Brown, Mrs. Reynolds, and Mr. Reynolds (collectively “the plaintiffs”) as well as Crown filed motions in limine seeking to preclude the opposing parties’ experts from testifying at trial. The trial court denied the motions and permitted the experts of both parties to testify at trial. During trial, the plaintiffs presented the testimony of Richard Jo-hannson (“Mr. Johannson”), a mechanical engineer, and Dr. Gerald Harris (“Dr. Harris”), a biomechanical engineer. Both Mr. Johannson and Dr. Harris opined that the injuries of Mr. Brown and Mrs. Reynolds would not have occurred had Crown installed rear doors on the operator compartments of the forklifts.
At the close of Crown’s proof, Crown renewed its motion to exclude the testimony of Mr. Johannson and Dr. Harris and moved for a directed verdict on all issues of liability. The trial court excluded the expert testimony of Mr. Johannson and Dr. Harris as unreliable under
McDaniel v. CSX Transportation, Inc.,
The Court of Appeals affirmed the judgment of the trial court. We granted review.
ANALYSIS
A. Overview of the Admissibility of Expert Testimony
Generally, questions pertaining to the qualifications, admissibility, relevancy, and competency of expert testimony are matters left to the trial court’s discretion.
McDaniel,
, Tennessee Rules of Evidence 702 and 703 govern the admissibility of expert testimony in Tennessee. Rule 702 states that “[i]f scientific, technical, or other specialized knowledge will substantially 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 in the form of an opinion or otherwise.” Rule 703 provides:
The facts or data in the particular case upon which an expert bases an opinion or inference may be those perceived by or made known to the expert at or before the hearing. If of a type reasonably relied upon by experts in the particular field in forming opinions or inferences upon the subject, the facts or data need not be admissible in evidence. The court shall disallow testimony in the form of an opinion or in *274 ference if the underlying facts or data indicate lack of trustworthiness.
The trial court, therefore, must determine that the expert testimony is reliable in that the evidence will substantially assist the trier of fact to determine a fact in issue and that the underlying facts and data appear to be trustworthy. In addition to these specific rules, evidence generally must be relevant to be admissible. See Tenn. R. Evid. 401, 402. The issue in the present case concerns the reliability of the testimony of the plaintiffs’ expert witnesses, Mr. Johannson and Dr. Harris.
In McDaniel, we listed several nonexclusive factors that courts could consider in determining the reliability of scientific testimony, including
(1) whether scientific evidence has been tested and the methodology with which it has been tested; (2) whether the evidence has been subjected to peer review or publication; (3) whether a potential rate of error is known; (4) whether ... the evidence is generally accepted in the scientific community; and (5) whether the expert’s research in the field has been conducted independent of litigation.
In addition to the
McDaniel
factors, we have identified other nondefinitive factors that a trial court may consider in assessing the reliability of an expert’s methodology. One such factor is the expert’s qualifications for testifying on the subject at issue.
Stevens,
Another factor that we have identified is the connection between the expert’s knowledge and the basis for the expert’s opinion.
Stevens,
We continue to emphasize, however, that these factors are non-exclusive and that a trial court need not consider all of these factors in making a reliability determination. Rather, the trial court enjoys the same latitude in determining how to test the reliability of an expert as the trial court possesses in deciding whether the expert’s relevant testimony is reliable.
Kumho Tire Co.,
B. Expert Testimony: Trial Court Proceedings
Mr. Johannson is a mechanical engineer with a professional engineering license. In 1970, Caterpillar hired him to aid in the redesign of its sit-down forklifts. While at Caterpillar, Mr. Johannson obtained sixteen patents for various devices on forklifts. In 1989, Mr. Johannson formed Concept Engineering, a private consulting firm that designs various machines for businesses.
Mr. Johannson offered two opinions regarding the circumstances surrounding the injuries to Mr. Brown and Mrs. Reynolds. He.testified that: 1) Crown was aware of the problem with left leg injuries and failed to take action to remedy the problem; and 2) a stand-up forklift with a properly latched door would have prevented the injuries suffered by Mr. Brown and Mrs. Reynolds.
The trial court found that it was required to apply all five of the McDaniel factors to Mr. Johannson’s testimony. 1 *276 The trial court first found that Mr. Jo-hannson failed to test his door design and offered “no evidence except for his bare-boned opinion regarding the pretrial testimony of the plaintiffs, various witnesses and the defendant’s accident reports.” As to factors two and three, the trial court reasoned that Mr. Johannson’s preliminary drawing of a door design could not be subjected to peer review and that the potential rate of error is unknown due to the lack of testing. In examining whether the evidence is generally accepted in the scientific community, factor four, the trial court explained that the scientific community “cannot possibly have any knowledge” of Mr. Johannson’s drawing and has rejected Mr. Johannson’s proposal to “ ‘just add doors and safety follows’ ” on prior occasions. Finally, the trial court found that Mr. Johannson had created his preliminary sketch for purposes of litigation. The trial court concluded its examination of Mr. Jo-hannson’s testimony by stating,
The Court does not dispute that the witness is an expert in his chosen field of engineering. The Court would not exclude this if he had any testing to back up his opinions; however, he does not. And the fact that he may be able to make a far more educated guess than a layperson, this does not make his opinion trustworthy.
Dr. Harris is a professor of biomedical engineering at Marquette University where he teaches courses in biomechanical engineering. He is also a licensed professional engineer. Dr. Harris’ work as a biomedieal/biomechanical engineer involves the application of mechanical engineering principles to the human body and the biomechanics of trauma or the study of the amount of force necessary to cause injuries to different parts of the body. This branch of biomechanics also evaluates the body’s position and how the position changes upon the occurrence of an accident or the application of a force. Dr. Harris also serves as director of research in the Department of Orthopedic Surgery at the Medical College of Wisconsin and collaborates with the Shriner’s Hospital in Chicago. He supervises two gait laboratories where he examines the movements and forces of a person’s legs, as well as a person’s ability to stand and maintain balance.
Dr. Harris offered opinions as to how Mr. Brown and Mrs. Reynolds were injured. Dr. Harris opined that 1) Mr. Brown and Mrs. Reynolds would not have been injured had their forklifts been equipped with doors; 2) the addition of a door would not increase the chances of injury during a tip-over or off-the-dock accident; and 3) the operator should remain inside the operator’s compartment during a tip-over or off-the-dock accident.
As with Mr. Johannson’s testimony, the trial court found that it was required to apply all five of the McDaniel factors to Dr. Harris’ testimony and addressed each factor in turn. The trial court concluded that 1) the doctor failed to offer support in the form of data and testing of his conclusion that the injuries would not have occurred if the forklifts had been equipped with doors; 2) Dr. Harris’ hypothesis had not been subjected to peer review; 3) the rate of error was unknown due to the doctor’s failure to test the hypothesis; 4) a determination of whether the evidence is *277 generally accepted in the scientific community could not be obtained due to Dr. Harris’ failure to submit any evidence; and 5) Dr. Harris’ opinions and conclusions came about through litigation. The trial court reasoned that:
Dr. Harris has conducted no testing, and he does not purport to rely on any testing which would support any of his conclusions. Dr. Harris has merely relied on his knowledge in the field of biomechanics. And, again, the Court has no reason to question Dr. Harris’ expertise as an expert in the field of biomechanics, but more is involved in this case than an expertise in the field of biomechanics. In this type of litigation, where the machinery in question is a highly specialized piece of equipment, an expert witness cannot rely on supposition or theories. An expert testifying that he knows what happened and how it could have been prevented may not do so absent any tests or research or reliable scientific method. Dr. Harris’ methodology appears to the Court to be little more than a consideration of the facts presented.
C. Application of the McDaniel Factors to the Testimony of Mr. Johannson and Dr. Harris
In the present case, the trial court concluded that it was required to apply all five of the
McDaniel
factors in assessing the reliability of the testimony of Mr. Johannson and Dr. Harris. Although a trial court has great latitude in assessing the reliability of expert testimony, we have never required a rigid application of the
McDaniel
factors in a reliability determination involving scientific or nonscientific expert evidence.
See Stevens,
The rigid application of the
McDaniel
factors to all expert testimony is problematic because all expert testimony may not “fit” within the factors. We agree with the United States Supreme Court that “we can neither rule out, nor rule in, for all cases and for all time the applicability of the factors ... nor can we now do so for subsets of cases categorized by category of expert or by kind of evidence.”
Kumho Tire Co.,
Upon reviewing the record, we conclude that both Mr. Johannson and Dr. Harris based their testimony primarily upon their practical experiences in them respective professions and that the testimony of neither expert fits neatly within the
McDaniel
factors. An expert may reach a conclusion from observations based upon his or her extensive and specialized experience.
Kumho Tire Co.,
1. Testing
In excluding the testimony of Mr. Johannson and Dr. Harris, the trial court emphasized their lack of testing to
*278
support their opinions. In rendering their opinions, however, both Mr. Johannson and Dr. Hands relied upon their review of Crown’s accident reports and reporting system, tests conducted by Crown, and other documents and materials from Crown. An expert may rely upon both data collected by others and tests performed by others in reaching his or her conclusions.
See Gussack Realty Co. v. Xerox Corp.,
In regard to the testing factor, the trial court also faulted Mr. Johann-son’s failure to develop and test the sketch of a door that he had presented. We recognize that some courts have excluded expert testimony of a safer alternative design where the expert did not create detailed drawings of the design or perform tests.
See, e.g., Zaremba v. Gen. Motors Corp.,
Furthermore, both Mr. Johannson and Dr. Harris testified that Crown has sold models of its stand-up forklifts equipped with doors. The fact that stand-up forklifts equipped with doors have been manufactured and placed on the market diminishes the need for tests, a prototype, and design development.
See McPike v. Corghi S.P.A.,
The trial court also emphasized Dr. Harris’ failure to test his conclusions regarding the actions that an operator should take in the event of a tip-over or off-the-dock emergency. Dr. Harris testified that from a biomechanic standpoint, an opera *279 tor involved in a tip-over or off-the-dock emergency should attempt to regain control of the forklift. If there is no time to react, the operator should stiffen and lean away from the impact zone.- Dr. Harris stated that training a wide variety of people to successfully jump off a forklift in the event of an emergency would be impossible due to differing work environments, work surfaces, operating speeds, and physical characteristics and reaction times of operators.
Contrary to Dr. Harris’ opinion, safety regulations instruct operators to exit compartments during these types of accidents. When an expert proposes a theory that modifies otherwise well-established knowledge, the importance of testing as a factor in determining reliability is at its highest.
Bitler v. A.O. Smith Corp.,
2. Peer Review
Although the trial court found that the opinions of neither Mr. Johannson nor Dr. Harris had been subjected to peer review, the lack of peer review does not necessarily render an expert’s opinion unreliable.
See Daubert,
3. Potential Rate of Error
The trial court found that the potential rate of error for the conclusions of Mr. Johannson and Dr. Harris is unknown due to lack of testing. The experienced-based methodology of the two experts, combined with Crown’s incorporation of a door on some of its stand-up forklifts, lessens the relevancy of the rate of error factor.
See Pipitone v. Biomatrix, Inc.,
4. General Acceptance
The trial court considered the general acceptance of the two experts’ opinions regarding the safety of stand-up forklifts that are not equipped with doors. In its ruling, the trial court referred to safety standards that do not require doors on stand-up forklifts. Those standards in-elude the American Society of Mechanical Engineers (ASME), the Occupational Safety and Health Administration (OSHA), the American National Standards Institute (ANSI), the National Institute for Occupational Safety and Health (NIOSH), and the military. ANSI and ASME are private, professional organizations,
3
and ANSI’s standards are “voluntary.”
4
Regulations from both 0'SHA and NIOSH are applicable to an employer’s conduct and not to a manufacturer’s conduct.
See
29 U.S.C. §§ 651-54, 669-71;
see also Minichello v. U.S. Indus., Inc.,
5. Research Conducted Independent of Litigation
Finally, the trial court found that the conclusions of Mr. Johannson and Dr. Harris were derived from litigation. Much of their testimony, however, was derived from pre-litigation personal experiences in their respective fields. As a result, the relevancy of this factor is lessened.
*281 Accordingly, we conclude that the trial court erred in holding that application of all five of the McDaniel factors was mandated and in applying the McDaniel factors when the factors did not provide an adequate measure of the reliability of the methodologies employed by Mr. Johannson and Dr. Harris. During the trial, the trial court expressed reservations as to the reliability of the testimony of Mr. Johannson and Dr. Hams. We, however, are unable to separate these expressions from the trial court’s mistaken belief that it was required to apply all five of the McDaniel factors. Rather, a trial court need only apply those McDaniel factors that it finds reasonably measure the reliability of the particular expert’s methodology. Therefore, we conclude that the trial court erred in excluding the testimony of both Mr. Johannson and Dr. Harris.
D. Directed Verdict
Having concluded that the trial court erred in excluding the testimony of Mr. Johannson and Dr. Harris, we now turn to the trial court’s decision to grant Crown’s motion for a directed verdict on the plaintiffs’ claims that the stand-up forklifts were defective or unreasonably dangerous.
5
We review a trial court’s decision to grant a directed verdict de novo, applying the same standards as employed by the trial court.
See Gaston v. Tenn. Farmers Mut. Ins. Co.,
Under the Tennessee Products Liability Act of 1978, “[a] manufacturer or seller of a product shall not be hable for any injury to a person or property caused by the product unless the product is determined to be in a defective condition or unreasonably dangerous at the time it left the control of the manufacturer or seller.” Tenn.Code Ann. § 29-28-105(a) (1980). Thus, the Act provides for recovery for injuries caused by a product that either is in a “defective” condition or is “unreasonably dangerous.”
Davis v. Komatsu Am. Indus. Corp.,
a product is dangerous to an extent beyond that which would be contemplated by the ordinary consumer who purchases it, with the ordinary knowledge common to the community as to its characteristics, or that the product because of its dangerous condition would not be put on the market by a reasonably prudent manufacturer or seller, assuming that the manufacturer or seller knew of its dangerous condition.
Id. at (8).
In determining whether a product is defective or unreasonably dangerous as to warrant liability, “the state of scientific and technological knowledge
*282
available to the manufacturer or seller at the time the product was placed on the market, rather than at the time of injury, is applicable.” Tenn.Code Ann. § 29-28-105(b) (1980). Moreover, “Consideration is given ... to the customary designs, methods, standards and techniques of manufacturing, inspecting and testing by other manufacturers or sellers of similar products.”
Id.
Evidence of a better, safer, or different design that might have avoided injury is insufficient to establish a design defect.
Shoemake v. Omniquip Int’l Inc.,
In granting Crown’s motion for a directed verdict, the trial court found that absent expert testimony, the plaintiffs failed to offer evidence that Crown’s forklifts were defective. The plaintiffs presented evidence through expert testimony, which we have held to be admissible, that Crown’s stand-up forklifts were unsafe for normal and reasonably anticipated handling and use due to the absence of a door. The plaintiffs’ experts further testified that the injuries to Mr. Brown and Mrs. Reynolds would not have occurred had the forklifts they were operating been equipped with doors. Upon viewing the evidence in a light most favorable to the plaintiffs as the nonmoving parties, we conclude that reasonable minds could disagree with the trial court’s conclusion that the plaintiffs failed to present proof of a defect.
In determining whether a product is unreasonably dangerous, we have interpreted the Tennessee Products Liability Act of 1978 as providing for two tests: the consumer expectation test and the prudent manufacturer test.
Ray ex rel. Holman,
Under the prudent manufacturer test, liability is imposed “in circumstances in which a reasonably prudent manufacturer with knowledge of a product’s dangerousness would not place the product in the stream of commerce.”
Ray ex rel. Holman,
Application of the prudent manufacturer test requires a risk-utility balancing of a number of factors, including (1) the product’s usefulness and desirability; (2) the product’s safety aspects-the likelihood and probable seriousness of injury; (3) the availability of a substitute product that would safely meet the same need; (4) the manufacturer’s ability to eliminate the product’s unsafe character without hindering its usefulness or causing the maintenance of its utility to be too expensive; (5) the ability of the operator or user to avoid danger through the exercise of care in using the product; (6) the user’s anticipated awareness of the product’s inherent *283 dangers and their avoidability; and (7) the feasibility of the manufacturer spreading the loss by setting the price of the product or maintaining liability insurance. Id. at 532-38, 533 n. 10.
In granting a directed verdict in favor of Crown, the trial court held that absent expert testimony the plaintiffs failed to offer proof that Crown’s forklifts were unreasonably dangerous. Through admissible expert testimony, the plaintiffs presented evidence regarding the likelihood and probable seriousness of injury to an operator of a stand-up forklift without a door and the operator’s inability to avoid the danger. The plaintiffs also provided expert proof that the inclusion of a door would prevent the injury without hindering the overall usefulness and safety of the product. Upon viewing the evidence in a light most favorable to the plaintiffs as the nonmoving parties, we conclude that reasonable minds could disagree with the trial court’s conclusion that the plaintiffs failed to present proof that Crown’s stand-up forklifts were unreasonably dangerous. Accordingly, the trial court erred in granting Crown’s motion for a directed verdict on the plaintiffs’ claims that Crown’s stand-up forklifts were defective and unreasonably dangerous.
CONCLUSION
We hold that the trial court erred in finding that application of all the McDaniel factors was mandated and in applying those factors when they failed to provide a reasonable measure of the reliability of the experts’ methodologies. We further conclude that the trial court erred in granting Crown’s motion for a directed verdict on the plaintiffs’ claims that Crown’s stand-up forklifts are defective and unreasonably dangerous. Accordingly, we reverse the judgment of the Court of Appeals and remand the case to the trial court for further proceedings consistent with this opinion.
Costs of appeal are taxed to the appel-lee, Crown Equipment Corporation, and its sureties, for which execution may issue if necessary.
Notes
. In its written order excluding the testimony of both Mr. Johannson and Dr. Harris, the trial court stated,
Tennessee has not adopted the Daubert standards, but instead requires a consideration of a nonexclusive list of factors to *276 determine an expert witness’s reliability. Among the factors that the Court must consider are those set out in the case of McDaniel v. CSX Transp., Inc.,955 S.W.2d 257 (Tenn.1997), rehearing denied,955 S.W.2d 257 (Tenn.1997), ce rt. denied,524 U.S. 915 ,118 S.Ct. 2296 ,141 L.Ed.2d 157 (1998).
(Emphasis added).
. John Sevart is a mechanical engineer who did not testify at trial. The plaintiffs contend that the trial court’s placement of rigid time constraints along with the trial court's requirements regarding the order of proof prevented the plaintiffs from presenting the expert testimony of John Sevart. According to the plaintiffs, Sevart would have testified regarding the propriety of a compartment door and the tests that he had conducted. The plaintiffs, however, failed to cite to the portion of the record where they sought to present Sevart's testimony and where the trial court' denied their request or provided the basis upon which the request was denied. Although Sevart’s affidavit is included in the record, the record does not contain an offer of proof by the plaintiffs suggesting that Sevart’s testimony would be consistent with his affidavit. Accordingly, we decline to address the issue.
. See "ANSI Overview," available at http:// www.ansi.org /about_ansi/overview /overview.aspx? menuid=l (last visited Sept. 26, 2005); "About ASME,” available at http:// www.asme. org/about (last visited Oct. 24, 2005).
. See "ANSI Overview,” supra note 3.
. The plaintiffs also contend that the trial court erred in granting a directed verdict on their failure to warn and failure to train claims. The plaintiffs, however, failed to raise these issues in the Court of Appeals. We decline to address these issues.
