In Texas, the rules of evidence that control the use of experts in trials are found in the 700 series of rules.  The judge is the “gatekeeper” to expert testimony and will only allow the expert testimony to be presented to the jury if specific requirements are met.  The current rules on experts were created by the United States Supreme Court in the case of Daubert v Merrill Dow Pharmaceuticals.

  • Judge is gatekeeper:  The trial judge has the job of gatekeeping or guaranteeing that expert testimony is actually “scientific knowledge”.
  • Relevance and reliability:  The trial judge must make sure that the expert’s testimony is relevant to the task at hand and rests on a reliable foundation.  Any concerns about expert testimony cannot be given to the jury as a question of the weight of the evidence.  Also, the Judge must find it more likely than not that the expert’s methods are reliable and reliably applied.
  • Scientific method/methodology: A conclusion will qualify as scientific knowledge if the proponent can show that it is the product of sound scientific methodology that uses the scientific method.
  • Factors:  Scientific methodology is the process of formulating hypotheses and conducting experiments to prove or disprove the hypothesis.  It is necessary to provide a nondispositive, nonexclusive, flexible set of observations considered relevant in order to determine the “validity” of any scientific testimony:
  1. Empirical testing: whether the theory or technique is falsifiable, refutable, and/or testable,
  2. whether it has been subjected to peer review and publication,
  3. the known or potential error rate,
  4. the existence and maintenance of standards and controls concerning its operation and
  5. the degree to which the theory and technique is generally accepted by a relevant scientific community.


       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, training, or education, may testify thereto in the form of an opinion or otherwise.


       The facts or data in the particular case upon which an expert bases an opinion or inference may be those perceived by, reviewed by, or made known to the expert at or before the hearing. If of a type reasonably relied upon by experts in the particular field in forming opinions or inferences upon the subject, the facts or data need not be admissible in evidence.


       Testimony in the form of an opinion or inference otherwise admissible is not objectionable because it embraces an ultimate issue to be decided by the trier of fact.


  1. Disclosure of Facts or Data. The expert may testify in terms of opinion or inference and give the expert’s reasons therefor without prior disclosure of the underlying facts or data, unless the court requires otherwise. The expert may in any event disclose on direct examination, or be required to disclose on cross-examination, the underlying facts or data.
  2. Voir dire. Prior to the expert giving the expert’s opinion or disclosing the underlying facts or data, a party against whom the opinion is offered upon request in a criminal case shall, or in a civil case may, be permitted to conduct a voir dire examination directed to the underlying facts or data upon which the opinion is based. This examination shall be conducted out of the hearing of the jury.
  3. Admissibility of opinion. If the court determines that the underlying facts or data do not provide a sufficient basis for the expert’s opinion under Rule 702 or 703, the opinion is inadmissible.
  4. Balancing test; limiting instructions. When the underlying facts or data would be inadmissible in evidence, the court shall exclude the underlying facts or data if the danger that they will be used for a purpose other than as explanation or support for the expert’s opinion outweighs their value as explanation or support or are unfairly prejudicial. If otherwise inadmissible facts or data are disclosed before the jury, a limiting instruction by the court shall be given upon request.