How to Evaluate the Reliability of An Expert Witness ?

In Nenno v. State, 970 S.W.2d 549, 561 (Tex. Crim. App. 1998), the court applied this test to evaluate the reliability of expert testimony from a special agent for the FBI who specialized in studying the sexual victimization of children. Id. at 562. The State called the agent to discuss the issue of future dangerousness in a death penalty case. Id. The court found that through interviews, case studies, and statistical research, a person could acquire superior knowledge concerning the behavior of such offenders. Id. In particular, the court found that the issue of future dangerousness is one that often surfaces in the course of research on sex offenders. Id. The court also observed that the lack of peer review for such research would go to the weight of the evidence and not its admissibility. Id. In Nenno, the Texas Court of Criminal Appeals stated that the test for reliability is: (1) whether the field of expertise is a legitimate one; (2) whether the subject matter of the expert's testimony is within the scope of that field; (3) whether the expert's testimony properly relies on and/or utilizes the principles involved in the field. Id. Rule 702 of the Texas Rules of Evidence requires that an expert be qualified "by knowledge, skill, experience, training, or education," and that his testimony will assist the trier of fact. TEX. R. EVID. 702. Thus, the trial court has a threshold responsibility for ensuring that an expert's testimony rests on a reliable foundation and is relevant to the issues of the case. Gammill v. Jack Williams Chevrolet, Inc., 972 S.W.2d 713, 728 (Tex. 1998). All expert testimony, not just novel, scientific testimony, must meet the fundamental requirements of reliability and relevance. Id. at 726. Experience alone may, in some cases, provide a sufficient basis for an expert's testimony. Id. An expert's testimony is sufficiently reliable if there is not too great an analytical gap between the data and the opinion proffered. Id. at 727. It should be noted that the trial court's gatekeeping function does not supplant cross-examination as the "traditional and appropriate means of attacking shaky but admissible evidence." Id. at 728.