Forensic Experts

Role and Duties of an Expert

The role of expert witnesses should be to give an impartial and unbiased assessment or interpretation of the evidence that the judge or party has asked them to consider. The admissibility of expert testimony is itself a vast area of law. Those practicing in the United States know that within U.S. jurisdictions admissibility is based on two tests derived from two important cases—the Frye test and the Daubert test.

The Frye test (also known as the general acceptance test) was stated in Frye v. United States(293 F. 1013, D.C. Cir., 1923): “Just when a scientific principle or discovery crosses the line between the experimental and demonstrable stages is difficult to define;… the thing from which the deduction is made must be sufficiently established to have gained general acceptance in the particular field in which it belongs.”

Subsequently in 1975, FRE 702 provided, “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, or training, or education may testify thereto in the form of an opinion or otherwise.”

Most jurists believed that rule 702 superseded Frye, and in 1993 the Supreme Court confirmed that in Daubert v. Merrell Dow Pharmaceuticals, Inc. (509 U.S. 579). This decision held that one must produce proof that establishes the scientific reliability of expert testimony before a federal court can admit it. Factors that judges could consider were the following:

• Whether the proposition is testable,
• Whether the proposition has been tested,
• Whether the proposition has been subjected to peer review and publication,
• Whether the methodology technique has a known or potential error rate,
• Whether there are standards for using the technique, and
• Whether the methodology is generally accepted.

Judges later explored in cases whether these principle applied to all experts—not just scientific experts. In 2000, the Supreme Court revised rule 702 to include as qualified all expert witnesses whose opinion testimony “is sufficiently based upon reliable facts or data, [if] the testimony is the product of reliable principles and methods, and [if] the witness has applied the principles and methods to the facts of the case.” Advisory Committee notes to rule 702 emphasized that if a witness is relying primarily on experience to reach an opinion, that witness must explain how that specific experience leads to that particular opinion.

...