WHEN CAN EXPERTS TESTIFY AND HOW DO THEY TESTIFY AND WHEN IS A WITNESSES’ OPINION ADMISSIBLE
The introduction of opinion testimony and the testimony of expert witnesses is governed by Article VII of the Colorado Rules of Evidence (CRE). Both lay and expert witnesses can testify as to their opinions, but the opinion testimony of lay witnesses is strictly limited. Opinion testimony of expert witnesses can cover many more areas, but is subject to its own set of safeguards.
CRE 701 governs opinions offered by lay witnesses. CRE 701 provides that a witness who is not an expert can offer an opinion only if it is “(a) rationally based on the perception of the witness and (b) helpful to a clear understanding of his testimony or the determination of a fact in issue.” For example, in a DUI case, the prosecution may call a lay witness to testify that the defendant appeared drunk to the witness, as long as the witness had an adequate opportunity to observe the defendant during the relevant time frame. Such an opinion would be rationally based on the witness’ perception of the defendant and helpful to the jury in deciding whether the defendant was under the influence.
CRE 702 sets forth the basic rule for experts: if scientific, technical or other specialized knowledge will help the jury understand the evidence or determine a fact in issue, then a witness who is qualified as an expert can offer an opinion on the evidence or the issue. Therefore, a trial court must first decide whether expert testimony will help the jury, then decide whether the proposed witness is qualified as an expert.
Deciding whether expert testimony will help the jury may be easy: an expert in ballistics has training and experience with guns and ammunition and can help the jury decide whether a particular shot was fired from a particular gun. If the proposed witness has special training and/or education and/or experience in ballistics, the trial court will likely allow the ballistics expert to testify as to his or her conclusion on that issue.
Sometimes, however, the determination whether the testimony will help the jury is more difficult. As scientific knowledge grows, and as the application of that knowledge in the forensic setting increases, courts are being asked to decide whether new scientific knowledge and cutting edge techniques are reliable enough to assist the jury. The use of DNA evidence is an excellent example. The scientific principles underlying DNA have been known and accepted for decades. The application of this knowledge to blood, saliva, other fluids or hair found at crime scenes is a relatively new innovation. Questions arise as to the integrity of the crime scene, the method of preserving the samples, the method of testing the samples, and the propriety of using statistics to generate an opinion that a particular substance almost certainly came from one particular individual.
Trial judges are asked to consider a wide range of factors when determining whether a particular technique or principle is reliable enough to allow a jury to hear testimony about it. In a case titled People v. Shreck, the Colorado Supreme Court suggested that a trial court consider 1) the reliability of the scientific principles, 2) the qualifications of the witness, 3) the usefulness of the testimony to the jury, 4) whether the technique can and has been tested, 5) whether the theory or technique has been subjected to peer review and publication, 6) the known or potential rate of error and the existence and maintenance of standards controlling the technique’s operation, 7) whether the technique has been generally accepted, 8) the relationship of the proffered technique to more established modes of scientific analysis, 9) the existence of specialized literature dealing with the technique, 10) the non-judicial uses to which the technique is put, 11) the frequency and type of error generated by the technique and 12) whether evidence has been offered in previous cases to support or dispute the merits of the procedure.
This list of factors is not exclusive: a trial court should consider the totality of the circumstances in each case; the factors listed by the Court may or may not be pertinent in any particular inquiry. Some factors may be more important in some inquiries than in others. At bottom, the trial court must make a basic determination that a particular principle or technique is reliable enough so that a jury should be allowed to consider it. Of course, opposing counsel remains free to attack the reliability of the testimony, and the jury remains free to accept or reject the testimony.
Expert testimony must be offered by an expert witness. In order to qualify as an expert, a witness must have some sort of specialized education, training or experience. While many experts have advanced degrees, such is not necessary. To paraphrase one famous formulation, if you want to know how a bee can fly, get expert testimony from an aeronautical engineer; if you want to know whether bees always take off into the wind, get expert testimony from a beekeeper.
CRE 703 provides that the information upon which an expert witness relies may be introduced to the jury if it is the sort of information upon which an expert in the filed would normally rely. This rule allows for the introduction of evidence that might otherwise be inadmissible, in order to help the jury understand the basis of the expert’s opinion.
CRE 704 provides that experts can even go so far as to testify as to the ultimate issue in a case. Thus, in a case alleging a defective product, an expert may testify that the product was, or was not, in fact defective; in a sanity trial, an expert may testify that the defendant was, or was not, insane.