Reasonable (Medical, Psychological, Scientific, Professional) Certainty
Terry Kukor, Ph.D., ABPP, and Meredith Veltri, Ph.D., ABPP
Netcare Forensic Center
June 2019
As best as can be determined, the “reasonable degree of certainty” formulation was first applied to scientific evidence in 1935, when a witness was “asked whether he could determine with reasonable scientific certainty the cause of the capsizing of the boat.” (Herbst v. Levy, 279 Ill. App. 353, 358, Ill. App. Ct. 1935). This term was not the mandate of the court but rather reflected a stylistic approach adopted by one of the lawyers working this case.
It was not until 1969 that this terminology was linked to the admissibility determination in the case of Twin City Plaza, Inc. v. Central Surety & Ins. Corp., 409 F.2d 1195, 1203 (8th Cir. 1969). To wit: “If the witness, based upon his background skill, possesses extraordinary training to aid laymen in determining facts and if he bases his answer upon what he believes to be reasonable scientific or engineering certainty, generally the evidence should be admitted, subject, of course, to the cross-examination of the adversary.” This statement was made without legal or scientific analysis as to what the term meant or why its use was being mandated.
Since that time, this phrase appears to have gradually become ingrained into forensic evaluation reports. One of the difficulties is the lack of uniform understanding about the precise meaning of this term. In their recent book on forensic report writing, Otto, DeMier, and Boccaccini (2014) concluded that the only consensus on this term is that the meaning is unclear. Melton et al., (2018) noted that the term represents an attempt to “transform probabilistic judgments into certain facts.”
A careful examination of relevant sources of authority raises questions about whether this term should be used in forensic reports. The term is not required by either the Frye test or Daubert trilogy of cases [Daubert, Joiner, and Kumho Tire], all of which address reliability, not certainty. This term is also not required by the Federal Rules of Evidence (FRE). In fact, FRE 702 speaks to reliability and sufficiency, not certainty. Given the lack of clear consensus on the meaning, use of this term could be potentially misleading for a jury. Per Ohio Rule of Evidence 403, misleading the jury is grounds for a mandatory exclusion of evidence.
At one time Ohio had apparently mandated the use of this term as precondition for admissibility. However, the Ohio Supreme Court has explicitly ruled in several different cases that the term is not required [see State v. Thompson, 23 N.E.3d 1096, 1129 (Ohio 2014); State v. Lang, 954 N.E.2d 596, 617 (Ohio 2011)]. In 2014, the Hawaii Supreme Court also confirmed that the term is not required.
Most recently, in 2016, the National Commission on Forensic Science (2016) recommended to the U.S. Attorney General that experts not use such language in reports or testimony. Later in 2016, the U.S. Attorney General issued a response to this recommendation directing federal Department of Justice prosecutors to abstain from use of this expression when presenting forensic reports or questioning forensic experts, unless required by a judge or law.
The conclusion to this tale? The Association of Ohio Forensic Evaluation Center Directors believes forensic examiners should be mindful about the concerns about “reasonable certainty” that have been made at the state and federal levels. We recommend that absent a clear directive from a judge to include this phrase, examiners should think twice about doing so.
The Ohio Forensic Directors hope to publish more research-based opinion pages as an opportunity to engage professionals in the discussion about their practice. Thank you to Drs. Kukor and Veltri for being our first contributors.