To a Reasonable Degree of Scientific Certainty: Understanding the DOJ’s Revised Guidance on Expert Scientific Testimony

Science, Technology, and the Law

To a Reasonable Degree of Scientific Certainty: Understanding the DOJ’s Revised Guidance on Expert Scientific Testimony

Many of us have watched television shows and movies, or perhaps even been present during a trial, where a given medical expert is on the stand as a witness, testifying about the forensic evidence relevant to the case at hand. As the attorneys wrap up their questioning of said expert, one question, normally asked with great emphasis for the jury, completes said testimony; do you believe these findings to a reasonable degree of scientific certainty? As of September 6, 2016, Attorney General Loretta Lynch released a memo to the Department of Justice officially banning the use of such a notorious phrase in expert scientific testimony among its various divisions.

Expert scientific testimony has been a revelation within American jurisprudence. Historically, the phrase “to a reasonable degree of scientific certainty” first appears on the record in the 1935 case of Herbst v. Levy, where the attorney in the case attempts to give credence to the witness’ testimony regarding evidence of certain events. 279 Ill. App. 353, 358 (1935). Fast forward some sixty odd years later, and the phrase appears again in the 1969 case of Twin City Plaza, Inc. v. Central Surety & Ins. Corp., this time being utilized to qualify a witness as an expert. 409 F.2d 1195, 1203 (8th Cir. 1969). The phrase has continued to set the bar for expert scientific witnesses, which is the norm in both criminal and civil trials today. This is in large part due to its ability to provide factfinders with a guidepost amidst a fog of highly technical and lengthy scientific testimony. The phrase, more so than the expert testimony itself, is often a gamechanger even among judges, given its brilliant ability to do one very important thing: attain or evade, reasonable doubt within the mind of a factfinder. American jurisprudence’s dependence on such “scientific certainty” is often seen as the single greatest influence on a jury or judge’s pursuit of proof beyond a reasonable doubt.

Yet, according to a recent report by the National Commission on Forensic Science, the phrase “to a reasonable degree of scientific certainty” has “no scientific meaning and may mislead factfinders [jurors or judges] when deciding whether guilt has been proved beyond a reasonable doubt.” Further, a 2016 report by the President’s Council of Advisors on Science and Technology stated that the phrase, “to a reasonable degree of scientific certainty”, “has no generally accepted meaning in science, implies certainty, and that expert witnesses ‘go beyond empirical evidence’ despite having no scientific basis for such opinions.” How could this be? How could such a familiar and impactful phrase that quite often sets the bar for reasonable doubt in many trials, be nothing more than junk science?

It appears the answer is rooted in science itself. A 2009 report from the National Academies of Sciences stated: “the fact is that many forensic tests–such as those used to infer the source of tool marks or bite marks – have never been exposed to stringent scrutiny.” The scientific community essentially condemned itself in this report, stating that “these techniques were developed in crime laboratories to aid in the investigation of evidence from a particular crime scene, and researching their limitations and foundations was never a top priority.” This comes as one of the biggest shocks from the DOJ’s recently released guidance; that the scientific community, which is fundamentally built on the scientific method, had failed to apply such a standard to their own techniques. The National Institute of Justice defines the scientific method consisting, generally, of four steps which include: (1) posing a question or hypothesis based on the appropriate background facts, knowledge, and information; (2) collecting and analyzing information; (3) evaluating and synthesizing that information; and (4) reaching a final conclusion. This method is what defines the scientific community and is the standard by which they peer review one another’s work, receive education and training and demonstrate that their findings amount to more than conjecture. Yet, the phrase has no true meaning in the scientific community outside of a courtroom, and the Federal Rules of Evidence that govern expert witnesses provides no requirement of its use in order to provide expert scientific testimony.

The DOJ’s 2016 guidance appears to be the federal government’s attempt to provide the American legal system with a new path forward when it comes to expert scientific testimony in hopes of severely decreasing the nearly 500 exonerations that occur each year due to scientific mistakes and inaccuracies. While the new guidance is certainly a step in the right direction, there is also the issue that many within the justice system, if not most, do not possess a basic understanding of the science presented during expert testimony. The fact remains that the law was not meant to be so reliant on modern science, yet modern American jurisprudence demands it. The question now becomes, where do we go from here when the majority of factfinders do not have a basic understanding of the science they are so often asked to interpret and provide judgment on?

Finding alternatives to this long-used phrase will certainly prove to be difficult, especially among attorneys that have clung to its persuasive value among jurors. The NCFC proposed a scientific and legal partnership that seeks to “identify appropriate language that may be used by experts to express conclusions and opinions to the trier of fact based on observations of evidence and data derived from evidence.” The Commission goes on to say that rather than use such meaningless phrases, “experts should make a statement about the examination itself, including an expression of the uncertainty in the measurement or in the data.” Based on this recommendation, a potential technique could be to have experts ground the basis of their expert opinions in reliable sources such a given study, as well as reiterating the restrictions on the evidence presented. This would better represent the true scientific process to the trier of fact, as well as provide a greater understanding of the evidentiary findings being put forth. Additionally, attorneys should work in tandem with the scientific community to ensure they can properly understand the forensic techniques utilized, as well as their evidentiary limitations, and develop appropriate language that can be understood by all.



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