"If scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue, a witness who is qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise" (Fed. R. Evid. 702). The admissibility of EXPERT TESTIMONY hinges on whether such testimony would help the judge or jury, and whether the witness is properly qualified as an expert. Expert witnesses may, and usually do, testify in the form of an opinion. The opinion must be supported by an adequate foundation of relevant facts, data, or opinions, rather than by conjecture. Thus, an expert frequently relies on firsthand or secondhand observations of facts, data, or opinions perceived prior to trial, or presented at trial during testimony or during a hypothetical question posed by an attorney. Courts do not require experts to have firsthand knowledge of facts, data, or opinions because experts in the field do not always rely on such firsthand knowledge. For instance, physicians routinely make diagnoses based on information from several sources, such as hospital records, X-ray reports, and opinions from other physicians.
When an expert offers a scientific fact as substantive evidence or as the basis of his or her opinion, the court must determine the reliability of the scientific fact by looking at such things as the validity of the underlying scientific principle, the validity of the technique applying that principle, adherence to proper procedures, the condition of instruments used in the process, and the qualifications of those who perform the test and interpret the results. Issues frequently arise over such scientific tools and techniques as lie detectors, DNA testing, and hypnosis. Some scientific tests, such as drug tests, radar, and PATERNITY blood tests, generally are accepted as reliable, and their admissibility may be provided for by statute.
In Kumho Tire Co. v. Carmichael 526 U.S. 137, 119 S.Ct. 1167, 143 L.Ed.2d 238 (U.S.Ala., Mar 23, 1999) (NO. 97-1709), a tire on the vehicle driven by Carmichael blew out, and the vehicle overturned, killing one passenger and injuring others. The survivors and decedent's representative brought a diversity suit against Kumho, the tire's maker, and its distributor. Their claim that the tire was defective relied mainly upon the depositions of a tire-failure analyst, whose expert testimony was to have been that a defect in the tire's manufacture or design caused the blow-out. The expert's opinion was based upon an inspection of the tire and upon the theory that in the absence of certain symptoms indicating tire abuse, a failure of the sort that occurred was caused by a defect. Kumho moved to exclude the expert's testimony, claiming that his methodology failed to satisfy Federal Rule of Evidence 702, which does not distinguish between "scientific" knowledge and "technical" or "other specialized" knowledge. The U.S. Supreme Court disagreed and ruled that the trial judge has the power to test the reliability of all expert testimony, whether by a scientific expert or by an expert who is not a scientist. The court held that Rule 702 does not address the testimony of scientists only, but that it applies to any type of expert testimony.
The AMERICAN MEDICAL ASSOCIATION maintains guidelines for physicians who testify both as treating physician experts and as nontreating expert witnesses. Many state medical associations also have guidelines for doctors who testify.
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