What Makes Scientific Evidence Reliable ?

Evidence Rule 702 provides that an expert witness may testify as to his opinion based on scientific knowledge if it will help the trier of fact understand the evidence or determine a fact in issue. A trial court's responsibility under Rule 702 is to determine whether proffered scientific evidence is sufficiently reliable and relevant to assist the jury. The proponent of the scientific evidence must demonstrate by clear and convincing evidence that the evidence is reliable. This is accomplished by showing the validity of the underlying scientific theory, the validity of the technique applying the theory, and proper application of the technique on the occasion in question. Factors that may affect reliability include, but are not limited to, the following: (1) the extent to which the underlying scientific theory and technique are accepted as valid by the relevant scientific community, if such a community can be ascertained; (2) the testifying expert's qualifications; (3) the existence of literature supporting or rejecting the underlying scientific theory and technique; (4) the technique's potential rate of error; (5) the availability of other experts to test and evaluate the technique; (6) the clarity with which the underlying scientific theory and technique can be explained to the court; (7) the experience and skill of the person who applied the technique on the occasion in question. While Rule 702 involves the "dual inquiry of relevance and reliability," the "overarching subject of Rule 702 is the scientific validity of the evidence at issue." In weeding out the so-called "junk" science, trial judges are called upon to serve as "gatekeepers." The proffered testimony must be sufficiently tied to the facts of the case that it will aid the jury in resolving a factual dispute.