What is expert evidence? According to Black's Law Dictionary,expert evidence is "fact or opinion evidence that purports to draw on specialized knowledge of a science or to rely on scientific principles for its evidentiary value". Evidence, Black's Law Dictionary (10th ed. 2014).
Because expert evidence is beyond the realm of judges’ and jurors’ everyday experiences, the prosecution and defense use expert witnesses to introduce evidence at trial. The Daubert Test is a method that federal district courts use to determine whether expert testimony is admissible under Federal Rule of Evidence 702, which generally requires that expert testimony consist of scientific, technical, or other specialized knowledge that will assist the fact-finder in understanding the evidence or determining a fact in issue. See Daubert v. Merrell Dow Pharms., Inc., 509 U.S. 579, 113 S.Ct. 2786 (1993).
During a pretrial Daubert hearing, a court will review the evidence outside the jury's presence. The proponent must show that the expert's underlying reasoning or methodology, and its application to the facts, are scientifically valid. In ruling on admissibility, the court considers the following factors:
In the federal court system, it replaced the Frye standard, which is still used in California, Illinois, Maryland, Minnesota, New Jersey, New York, Pennsylvania, and Washington.See Frye v. United States, 293 F. 1013 (D.C. Cir. 1923).
In Virginia, the standard for admissibility of expert evidence comes from Spencer v. Commonwealth, 393 S.E. 2d 609, 240 Va. 78 (2008). In Spencer, the Virginia Supreme Court held that when expert evidence is offered, a court "must make a threshold finding of fact with respect to the reliability of the method offered," unless: 1) it is a type of evidence "so familiar and accepted as to require no foundation to establish the fundamental reliability of the system, such as fingerprint analysis;" 2) it is so unreliable "that the considerations requiring its exclusion have ripened into rules of law, such as "lie-detector" tests;" or 3) its admission is required or regulated by statute, such as blood-alcohol concentration test results. The court will usually have to rely on expert testimony to make the threshold finding of fact; if there is a conflict, the finding will not be disturbed on appeal as long as the trial court's finding is supported by credible evidence. Even in the case where there is a dispute about the reliability of expert evidence, the court may, in its discretion and if it determines that there is a sufficient foundation, admit the evidence "with appropriate instructions to the jury to consider the disputed reliability of the evidence in determining its credibility and weight." Unanimity is not required, and the court has wide discretion to determine whether the evidence is reliable enough to be put before the jury. Spencer, 393 S.E.2d at 621.