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The History of "Reasonable Degree of Certainty"

Date Published
January 17, 2018

Sidebar to the article Uncertainty Ahead: A Shift in How Federal Scientific Experts Can Testify, by Danielle Weiss and Gerald LaPorte, published in NIJ Journal issue no. 279.

According to a document issued by the National Commission on Forensic Science (NCFS)[1] “reasonable degree of certainty” was first used — not legally mandated — in Herbst v. Levy in 1935, when the plaintiffs’ expert, Fred Ludolph, testified about the circumstances of a capsized boat. Ludolph was “then given a hypothetical question containing some of the facts in evidence relating to the speed of the boat, the number of passengers, the condition of the water, and other circumstances, and asked whether he could determine with reasonable scientific certainty the cause of the capsizing of the boat.”[2]

It was not until 1969 that the terminology was linked to the admissibility determination. In Twin City Plaza, Inc. v. Central Sur. (1969), the court wrote:

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. The weaker the scientific opinion or the less qualified the expert, the more vigorous will be the cross-examining attack and undoubtedly the less persuasive will be the opinion to the trier of fact.[3] [emphasis added with underline]

According to NCFS, this statement was made without legal or scientific analysis as to what the term meant or why its use was being mandated.

About This Article

This article was published as part of NIJ Journal issue number 279, published April 2018, as a sidebar to the article Uncertainty Ahead: A Shift in How Federal Scientific Experts Can Testify, by Danielle Weiss and Gerald LaPorte.

[note 1] Views of the Commission Regarding Use of the Term "Reasonable Scientific Certainty," National Institute of Standards and Technology.

[note 2] Herbst v. Levy, 279 Ill. App. 353, 358 (Ill. App. Ct. 1935).

[note 3] Twin City Plaza, Inc. v. Central Sur. INS, 409 F.2d 1195, 1203 (8th Cir. 1969).

National Institute of Justice, "The History of "Reasonable Degree of Certainty"," January 17, 2018, nij.ojp.gov:
Date Created: August 6, 2019