A Scientific Approach to Scientific Evidence: A Four-Stage Rule for Admissibility and Scope
Utilizing Forensic Science in Criminal Cases, 2014 Edition, Thomson Reuters/Aspatore (2013), Westlaw: 2013 WL 5757941
13 Pages Posted: 24 Dec 2015 Last revised: 30 Dec 2015
Date Written: November 1, 2013
Scientific or expert testimony can be a critical factor in a criminal jury trial. After years of trying cases, litigating admissibility of scientific and expert testimony in a variety of state and federal courts, and studying the subject academically, it is clear that there is little consistency in the determination of admissibility and scope of such evidence. The rules and the case law, both state and federal, are at best a mosaic and at worst a jumble. The trial judge is the “gatekeeper,” but most judges and most trial lawyers do not have a clear protocol to take a scientific approach to determine the admissibility or scope of scientific or expert evidence. To that end, we will break the determination of admissibility and scope into a four-stage process.
In this chapter, we will cover the four-stage rule that will guide the trial judge and the trial lawyer in determining whether to allow a witness who is a scientist (or expert) to testify and in determining the scope of that to which the witness should be allowed to testify. The four-stage rule is intuitive, based on science, and consistent with federal and state jurisprudence.
The four-stage rule imposes on the court the duty to ask:
1. Whether a proffered science (or area of expertise) is a science (or area of expertise); 2. Whether the proffered witness is a scientist (or expert) in this particular area of science (or expertise); 3. Whether the data is reliable; and finally, and only after the first three stages are met; 4. What a true scientist (or expert) can say based on the science and based on the reliable data.
We will first discuss the foundation for this four-stage rule. There is support for it in both the federal and the state rules and case law. Most important, the four stages are based on a scientific and logical approach to admissibility of, and the limitations on the scope of, any scientific or expert testimony.
Keywords: Scientific evidence, forensic, gatekeeper
JEL Classification: K14
Suggested Citation: Suggested Citation