In 1923, the U.S. Supreme Court decided the landmark case of Frye v. United States. In that case, attorneys were attempting to enter into evidence information from a polygraph test. The Court ruled that scientific evidence can be admissible if it has "gained general acceptance in the particular field to which it belongs." This is sometimes referred to as the "general acceptance" standard.
The Frye decision held until 1993, at which point the U.S. Supreme Court heard Daubert v. Merrell Dow Pharmaceuticals. In this case, the Court unanimously ruled that scientific evidence can only be admissible if it meets the following criteria:
- It must be subject to empirical testing: the theory or technique must be falsifiable, refutable, and testable.
- It must be subjected to peer review and publication.
- It must have a known potential error rate.
- The existence and maintenance of standards and controls concerning its operation must be in place.
- It must, to some degree, conform to theory and technique that is generally accepted by a relevant scientific community.
It is interesting to note that, due to a 1998 ruling in United States v. Sheffer, the Court found that procedures that appear to be valid and reliable must be closely scrutinized using the Daubert standard. Most courts do not consider psychological expert testimony that involves only clinical/medical judgment (i.e., it does not involve tests or assessment procedures) to be subject to the Daubert standard. However, if a psychologist uses tests or assessment procedures that give the appearance of "infallibility," then that testimony's admissibility hinges on whether the procedures meet the Daubert standard.
So, what does this mean? Essentially, a psychologist or psychiatrist can say whatever he/she wants to about a particular case, and it can be entered into evidence as long as that testimony is only based only on the professional's clinical/medical judgment (even if that judgment is absolutely incorrect). As soon as a professional starts using tests and procedures that increase the accuracy of clinical/medical opinions, his/her testimony must be held to a higher standard.
NOTE: The standards I discussed above apply to federal cases only. Many states have adopted similar standards, and are often referred to as "Frye states" or "Daubert states." In Colorado, the decision in People v. Shreck (2001) dictates the following: "Under the standard established in this rule [Rule 702, Colorado Court Rules of Evidence, Testimony By Experts], the trial should focus on the reliability and relevance of the scientific evidence and determine the reliability of the scientific principles, the qualifications of the witness, and the usefulness of the testimony to the jury. In determining the reliability and relevance of the evidence, the court should apply a broad inquiry and consider the totality of the circumstances in each specific case, considering a wide range of factors. Because the applicable standard is so liberal, the court should also apply its discretionary authority under C.R.E. 403 to ensure the probative value of the evidence is not substantially outweighed by unfair prejudice."
In my experience, the Shreck standard allows for the vast majority of the data a psychologist or psychiatrist could produce (no matter the quality of the data) to be entered into evidence.
Thanks for reading-- Max Wachtel, Ph.D.