Reasonable Scientific Certainty

From the DOJ / NIST / National Commission on Forensic Science (link)

Document title: Testimony using the term “Reasonable Scientific Certainty”

Statement of the Issue:

"Forensics experts are often required to testify that the opinions or facts stated are offered “to a reasonable scientific certainty” or to a “reasonable degree of [discipline] certainty.” Outside of the courts, this phrasing is not routinely used in scientific disciplines. Moreover, the terminology, in its varying forms, is not defined in standard medical or scientific reference materials. With respect to its use in the courts, this phrase is almost always interjected as a matter of custom, but in some jurisdictions results from an appellate court ruling or trial judges’ or lawyers’ belief that it is a necessary precondition for admissibility. In the courtroom setting, the phrase risks misleading or confusing the factfinder.

It is the view of the National Commission on Forensic Science (NCFS) that the scientific community should not promote the use of this terminology. Additionally, the legal community should recognize that medical professionals and other scientists do not routinely use “to a reasonable scientific certainty” when expressing conclusions outside of the courts since there is no foundational scientific basis for its use. Therefore, legal professionals should not require that forensic discipline testimony be admitted conditioned upon the expert witness testifying that a conclusion is held to a “reasonable scientific certainty,” a “reasonable degree of scientific certainty,” or a “reasonable degree of [discipline] certainty,” as such terms have no scientific meaning and may mislead jurors or judges when deciding whether guilt has been proved beyond a reasonable doubt. The Commission recognizes the right of each court to determine admissibility standards but expresses this view as part of its mandate to “develop proposed guidance concerning the intersection of forensic science and the courtroom.”

Read the rest here (link).