Admissibility of scientific evidence

What makes some scientific evidence admissible? Who makes this decision? These questions formed the basis of a recent article in the Journal of the New York State Bar Association entitled “Scientific proof: the court’s role as gatekeeper for admitting scientific expert testimony.” The first item of note is that in our legal system, the trial court judge is accorded tremendous responsibility and leeway in deciding what type of scientific evidence to allow at trial as well as its method of presentation to the trier of fact. In essence, there is a bifurcation, since the trial judge becomes the trier of law, deciding who may testify, what they may testify about, and the method of presentation concerning the evidence. The jury then becomes the trier of fact, deciding to what degree each expert witness is to be believed, how much of all the evidence proffered or submitted should be considered, and the weight that should be given to any evidence. The article noted that “The trial courts are entrusted with the duty of gatekeeper when reviewing the admissibility of scientific expert testimony. The intention is to eliminate junk science and ensure that jurors only hear reliable expert testimony which will assist them in understanding key issues of fact presented at trial.”

Ninety-some years ago, in Frye v United States (293 F 1013, DC Cir Ct App, 1923), the “general acceptance standard” was espoused; despite numerous court rulings further defining and tweaking this standard, the general acceptance standard or test is still in play today, particularly at the state level. The court in Frye noted

Somewhere in this twilight zone the evidential force of the scientific principle must be recognized, and while courts will go a long way in admitting expert testimony deduced from a well-recognized scientific principle or discovery, the thing from which the deduction is made must be sufficiently established to have gained general acceptance in the particular field in which it belongs.

About 40 years ago, the Federal Rules of Evidence, which has since been adopted by every state in one form or another, added rule 702 that specifically addressed the admission of expert testimony. This rule states that qualified experts (again, this determination rests within the purview of the trial judge) may testify and give their opinion or other testimony when

(a) the expert’s scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue; (b) the testimony is based on sufficient facts or data; (c) the testimony is the product of reliable principles and methods; and (d) the expert has reliably applied the principles and methods to the facts of the case.

Fast forward 20 years to Daubert v Merrell Dow Pharmaceuticals, Inc. (509 US 579, 1993). We find that the Supreme Court decreed that rule 702 supersedes Frye at least at the federal level, in that expert testimony now must be based more on its scientific validity than on its acceptance in the scientific community. The trial court judge became the gatekeeper with the responsibility to “scrutinize the reliability of any expert evidence offered” and, in addition, must ensure that (1) any expert testimony is derived from scientific knowledge, (2) such scientific knowledge is relevant to the issues being discussed, and (3) such scientific evidence rests on a reliable foundation.

Daubert essentially laid down 4 considerations in determining the admissibility of scientific expert testimony. The first is whether the theory or technique being proposed has been tested in the scientific community to which it applies. The second is whether the theory or technique has been subjected to peer review in the scientific community in which it resides. The third is that any potential rate of error must be duly noted. Finally, the fourth is a determination as to whether the theory or technique being proposed has been generally accepted in the expert’s professional community. Five years later, in Kumho Tire Co. v Carmichael (526 US 137, 1999), Daubert was extended to all expert testimony, not just scientific expert testimony.

The article noted that it was still possible for junk science to make its way into the courtroom because “The broad standard for review for admitting scientific expert testimony places a heavy burden on the trial court to examine proffered scientific evidence and determine its reliability. This may result in admitting scientific testimony which is nonetheless unreliable or disputed within the scientific community.” After discussing a few high-profile cases in which dubious scientific testimony was allowed, the article concluded with the opinion that all of the standards—Frye, Daubert, and the Federal Rules of Evidence—have one common goal, which is “to admit reliable and generally accepted scientific evidence that will assist a jury in understanding the key issues at trial.” It also noted that all of these safeguards are not foolproof, error free, or infallible. “Novel science…may result in the admissibility of potentially unreliable evidence which may later be refuted by further advancements in science. Likewise,…one can be convicted based upon scientific expert theory that is later deemed unacceptable in the scientific community.”


It is well known that, historically, time has a way of changing the validity of science. Orthodontics is a classic example of how what one espouses today as gospel will tomorrow be viewed as hypocrisy, whereas what seems to be fringe science today will someday be seen as a tenet of our thinking. Sure, there are certain constancies. Take basic Newtonian physics; I don’t see that changing a whole lot in the future. However, in my lifetime alone, I have seen the definition of centric relation change 3 times. Some of orthodontics is based on hard science. Some of it is based on soft science. For better or worse, as a specialty we are simultaneously a science, an art, and a business.

Clinical orthodontics allows really astute clinicians to do the wrong thing for the right reason and come out with a wonderful result. This is because many of our patients are multifactorial in terms of etiology, clinical development, differential diagnostic assessment, and responsiveness to various mechanotherapeutic approaches, and are subject to the whims of nature, growth, aging, environmental influences, and appliance interventions with regard to retention and stability. We have scant evidence that only one way is appropriate in any situation. We have scant scientific evidence of cause and effect and of a direct and assured response to a given clinical approach at the expense of other alternatives. We see patients differently, as shown by the variety of treatment goals applicable to any patient based on esthetic norms and accepted variations. We are a specialty rife with viable alternatives.

Our scientific community is at odds with our clinical community. Our clinical community is a house divided. Is it any wonder that we have leaders and followers going off in different directions, carrying their various banners on high, decrying the efforts and approaches of colleagues, all in the name of “mine is faster, better, easier, more dollar friendly (or whatever) than yours”?

It might sound as if I don’t like where we are, but in a weird sort of way I do. I love orthodontics. I love the interpretive freedom it affords when I discuss treatment goals and objectives with my patients based on not only my beliefs but also theirs: their desires and needs, whether esthetic, social, clinical, temporal, fiscal, and so on. I adore clinical practice: the way that there are innumerable ways to treat a patient regarding interventional timing, the type of appliance used, the prescription espoused among our appliance systems, auxiliary use, retention modality, and so on. I can’t imagine many other careers as rewarding as ours in terms of self-satisfaction; service to our patients for enhancing their self-esteem and persona; security; and role modeling. And let’s not forget that we make a good living from our ministrations. I could go on, but it’s all been said before.

This article was about the science of orthodontics from the evidentiary perspective. I have never thought of it as a hard science. I just don’t see our specialty as being wired that way. There is no harm in trying. I applaud those trying to apply hard scientific testing to orthodontics with the goal of producing hard evidence, diagnostic evidence, or treatment evidence. I just don’t know whether we will ever get what we think we want. Don’t get me wrong. We’ll learn a few things, we’ll narrow the perspective, we’ll hone the approach a little, but I don’t see us getting very far past Frye’s “general acceptance” standard.

General acceptance means that there are many ways to look at a patient. General acceptance means that there may be several viable treatment plans based on the varying goals and objectives of treatment developed in conjunction with our patients. General acceptance means that there are many ways to treat a certain problem and many philosophies of retention. General acceptance by our entire specialty means that there ain’t just one way.

Those who really must hear this are our “experts”: those who would go into court and chastise, castigate, or emasculate, and try to destroy the professionalism and credibility of a colleague who is either a defendant or an opposing expert. These are the dangerous ones; these are the heretics in our midst. Experts should recognize that the world, particularly the orthodontic world, is not black or white. There is a lot of gray out there. Yes, sometimes errors are made; okay, fine. But differing views and approaches are not failures that need addressing or redress. They can be as simple as beliefs and approaches that have gained some degree of general acceptance in a professional community and thus have just as much right to exist as the beliefs of the next guy or the next expert.

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Apr 6, 2017 | Posted by in Orthodontics | Comments Off on Admissibility of scientific evidence

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