While not all expert witnesses are scientists, many of them are. This has led to a recognition that science and law are philosophically different, and that their pursuits follow different constructs. See generally The Age of Expert Testimony: Science in the Courtroom, Report of a Workshop (National Academies Press 2002) Catalog No. 10272; http://www.nap.edu/catalog/10272.html (“Report”).
The Report notes that scientists may be uncomfortable in the courtroom because the courtroom construct – using the adversary method to resolve differences – is foreign to them professionally. Scientists look for consensus, not victory and defeat. While each trial has a winner and a loser; this is not the outcome of scientific gatherings such as university seminars and professional meetings. The Report notes that the basis of the scientific construct is the “scientific method,” by which hypotheses are tested and proved false or not false. The essence of science is refutability. The approach to truth is iterative.
Refutability has no real analog in the legal construct. In a courtroom, “truth” is what a jury says it is. Even in the case of irreconcilable opinions, such as whether a soldier’s cancer was caused by agent orange, the scientist might say “we don’t know.” There is no “truth.” But the witnesses, and the trier, will ultimately reach a “truth,” through an evaluation using unknown factors and intangible considerations leading to a “yes-or-no” conclusion that may not be reproducible. Another judge or jury could reach a different result. And no matter how many trials and verdicts are obtained, we’re no closer to knowing whether agent orange caused cancer. The lack of a known error rate and the irreproducibility of the legal result are the antitheses of science. Yet the courtroom demands it.
Law is also guided by policy, which is not a scientific construct at all. Scientists are sometimes called on to testify as to whether something is safe. But, that is not a scientific conclusion. It is a conclusion based on what society deems an acceptable risk. When Ford’s witness says that the Pinto is “safe,” he’s straying from science. “Safe” is not a scientific construct, yet it’s written into many laws and regulations. And so when the inevitable testimony is presented, there is a philosophical collision.
In addition, scientists are used to presenting data and conclusions drawn from them, such as in the relatively collegiate setting of a professional meeting or a university seminar. There, colleagues nudge and probe with the usual goal of advancing overall scientific knowledge through gentle questioning and friendly constructive suggestion. In a sense, in such a setting, the goal is universal – to advance knowledge.
Conversely, the environment in a courtroom is decidedly hostile. The scientist is subjected to lengthy and often destructive questioning, the point of which is to destroy his credibility and that of his testimony. It is not the advancement of science or furtherance of scientific knowledge. Some have said that science is forward looking and that law is backward looking – trying to unscramble something that happened in the past.
In the world of science, the expert is rarely an advocate for a side or an individual, but rather for a hypothesis. Did an asteroid kill the dinosaurs? As more data are collected, the evidence accumulates. But we don’t need a decision by Friday. Their work is not focused on individual outcomes. Scientists speak more broadly about populations and groups of data. A scientist might note that as a group, flight attendants have a higher incidence of lung cancer, all other things being equal. That said, the scientist could never opine in scientific circles that a particular lung cancer was occupationally caused. The data aren’t there. When the flight attendant sues the airline, he’ll want a definitive answer. The scientist is not equipped professionally to give one. Under pressure, a scientist might say something in court she’d never say at a professional meeting or in a manuscript for a peer-reviewed journal.
It is important during expert witness preparation to review these philosophical points with the witness, and to acknowledge an understanding of the differences in approach between the courtroom and the laboratory. It is important, also, to keep these ideas in mind when considering the trier’s receipt of expert testimony. The trier will want relative certainty, not equivocation as might be the more scientific approach. But, equivocation is not weakness. This will make for a smoother trial.
Finally, it should be noted that in federal court, it is recognized that the backgrounds of judges frequently does not include science. Accordingly, the Federal Judicial Center and the National Academy of Sciences have published a “Reference Manual on Scientific Evidence,” now in its Third Edition (2011). Its purpose is to It is available on-line. I am not aware of any state analog in Colorado.
 The author does not completely agree with this point.