The National Commission on Forensic Science has called for the attorney general of the United States to replace the term of “reasonable degree of certainty.” 

According to the National Commission: 

      There is no common definition of reasonable certainty. Therefor whether convinced as “scientific certainty” or [discipline] certainty the term is idiosyncratic to the witness. 

Here are the commission’s three recommendations: 

  • Recommendation #1: The Attorney General should direct all attorneys appearing on behalf of the Department of Justice (a) to forego use of these phrases when presenting forensic discipline testimony unless  directly required by judicial authority as a condition of admissibility for the witness’ opinion or conclusion, and (b) to assert the legal position that such terminology is not required and is indeed misleading. 
  • Recommendation #2: The Attorney General should direct all forensic science service providers and forensic science medical providers employed by Department of Justice not to use such language in reports or  couch their testimony in such terms unless directed to do so by judicial authority. 
  • Recommendation #3: The Attorney General should, in collaboration with NIST, direct the OSACs to develop appropriate language that may be used by experts when reporting or testifying about results or findings  based on observations of evidence and data derived from evidence.


It is too early to tell what impact these proposed changes will have, if any, on expert testimony.