Science in the Courtroom

By Stephen Breyer

In this age of science, science should expect to find a warm welcome, perhaps a permanent home, in our courtrooms. The legal disputes before us increasingly involve the principles and tools of science. Proper resolution of those disputes matters not just to the litigants, but also to the general public—those who live in our technologically complex society and whom the law must serve. Our decisions should reflect a proper scientific and technical understanding so that the law can respond to the needs of the public.

Consider, for example, how often our cases today involve statistics, a tool familiar to social scientists and economists but, until our own generation, not to many judges. Only last year, the US Supreme Court heard two cases that involved consideration of statistical evidence. In Hunt v. Cromartie, we ruled that summary judgment was not appropriate in an action brought against various state officials that challenged a congressional redistricting plan as racially motivated in violation of the Equal Protection Clause. In determining that disputed material facts existed regarding the motive of the state legislature in redrawing the redistricting plan, we placed great weight on a statistical analysis that offered a plausible alternative interpretation that did not involve an improper racial motive. Assessing the plausibility of this alternative explanation required knowledge of the strength of the statistical correlation between race and partisanship, understanding of the consequences of restricting the analysis to a subset of precincts, and understanding of the relationships among alternative measures of partisan support.

In Department of Commerce v. United States House of Representatives, residents of a number of states challenged the constitutionality of a plan to use two forms of statistical sampling in the upcoming decennial census to adjust for expected “undercounting” of certain identifiable groups. Before examining the constitutional issue, we had to determine whether the residents challenging the plan had standing to sue because of injuries they would be likely to suffer as a result of the sampling plan. In making this assessment, it was necessary to apply the two sampling strategies to population data in order to predict the changes in congressional apportionment that would most likely occur under each proposed strategy. After resolving the standing issue, we had to determine whether the statistical estimation techniques were consistent with a federal statute.

In each of these two cases, we judges were not asked to become expert statisticians, but we were expected to understand how the statistical analyses worked. Trial judges today are routinely asked to understand statistics at least as well, and probably better.

The legal disputes before us increasingly involve the principles and tools of science.

But science is far more than tools such as statistics. And that “more” increasingly enters directly into the courtroom. The Supreme Court, for example, has recently decided cases involving basic questions of human liberty, the resolution of which demanded an understanding of scientific matters. In 1997, we were asked to decide whether the Constitution contains a “right to die.” The specific legal question was whether the federal Constitution, which prohibits government from depriving “any person” of “liberty” without “due process of law” requires a state to permit a doctor’s assistance in the suicide of a terminally ill patient. Is the “right to assisted suicide” part of the liberty that the Constitution protects? Underlying the legal question was a medical question: To what extent can medical technology reduce or eliminate the risk of dying in severe pain? The medical question did not determine the answer to the legal question, but to do our legal job properly, we needed to develop an informed, although necessarily approximate, understanding of the state of that relevant scientific art.

Nor are the right-to-die cases unique in this respect. A different case in 1997 challenged the constitutionality of a state sexual psychopath statute. The law required a determination of when a person can be considered so dangerous and mentally ill that the threat he or she poses to public safety justifies indefinite noncriminal confinement, a question that implicates science and medicine as well as law.

The Supreme Court’s docket is only illustrative. Scientific issues permeate the law. Criminal courts consider the scientific validity of, say, DNA sampling or voiceprints, or expert predictions of defendants’ “future dangerousness,” which can lead courts or juries to authorize or withhold the punishment of death. Courts review the reasonableness of administrative agency conclusions about the safety of a drug, the risks attending nuclear waste disposal, the leakage potential of a toxic waste dump, or the risks to wildlife associated with the building of a dam. Patent law cases can turn almost entirely on an understanding of the underlying technical or scientific subject matter. And, of course, tort law often requires difficult determinations about the risk of death or injury associated with exposure to a chemical ingredient of a pesticide or other product.

Patent law cases can turn almost entirely on an understanding of the underlying technical or scientific subject matter.

The importance of scientific accuracy in the decision of such cases reaches well beyond the case itself. A decision wrongly denying compensation in a toxic substance case, for example, can not only deprive the plaintiff of warranted compensation but also discourage other similarly situated individuals from even trying to obtain compensation and can encourage the continued use of a dangerous substance. On the other hand, a decision wrongly granting compensation, although of immediate benefit to the plaintiff, can improperly force abandonment of the substance. Thus, if the decision is wrong, it will improperly deprive the public of what can be far more important benefits. The upshot is that we must search for law that reflects an understanding of the relevant underlying science, not for law that frees companies to cause serious harm or forces them unnecessarily to abandon the thousands of artificial substances on which modern life depends.

The search is not a search for scientific precision. We cannot hope to investigate all the subtleties that characterize good scientific work. A judge is not a scientist, and a courtroom is not a scientific laboratory. But the law must seek decisions that fall within the boundaries of scientifically sound knowledge.

Even this more modest objective is sometimes difficult to achieve in practice. The most obvious reason why is that most judges lack the scientific training that might facilitate the evaluation of scientific claims or the evaluation of expert witnesses who make such claims. Judges typically are generalists, dealing with cases that can vary widely in subject matter. Our primary objective is usually process-related: seeing that a decision is reached fairly and in a timely way. And the decision in a court of law typically (though not always) focuses on a particular event and specific individualized evidence.

A judge is not a scientist, and a courtroom is not a scientific laboratory. But the law must seek decisions that fall within the boundaries of scientifically sound knowledge.

Furthermore, science itself may be highly uncertain and controversial with respect to many of the matters that come before the courts. Scientists often express considerable uncertainty about the dangers of a particular substance. And their views may differ about many related questions that courts may have to answer. What, for example, is the relevance to human cancer of studies showing that a substance causes some cancers, perhaps only a few, in test groups of mice or rats? What is the significance of extrapolations from toxicity studies involving high doses to situations where the doses are much smaller? Can lawyers or judges or anyone else expect scientists always to be certain or always to have uniform views with respect to an extrapolation from a large dose to a small one, when the causes of and mechanisms related to cancer are generally not well known? Many difficult legal cases fall within this area of scientific uncertainty.

Finally, a court proceeding, such as a trial, is not simply a search for dispassionate truth. The law must be fair. In our country, it must always seek to protect basic human liberties. One important procedural safeguard, guaranteed by our Constitution’s Seventh Amendment, is the right to a trial by jury. A number of innovative techniques have been developed to strengthen the ability of juries to consider difficult evidence. Any effort to bring better science into the courtroom must respect the jury’s constitutionally specified role, even if doing so means that, from a scientific perspective, an incorrect result is sometimes produced.

Despite the difficulties, I believe that there is an increasingly important need for law to reflect sound science. I remain optimistic about the likelihood that it will do so. It is common to find cooperation between governmental institutions and the scientific community where the need for that cooperation is apparent. Today, as a matter of course, the president works with a science adviser, Congress solicits advice on the potential dangers of food additives from the National Academy of Sciences (NAS), and scientific regulatory agencies often work with outside scientists as well as their own to develop a product that reflects good science.

Any effort to bring better science into the courtroom must respect the jury’s constitutionally specified role.

The judiciary, too, has begun to look for ways to improve the quality of the science on which scientifically related judicial determinations will rest. The Federal Judicial Center is collaborating with NAS in developing the academy’s Program in Science, Technology, and Law. This program will bring together on a regular basis knowledgeable scientists, engineers, judges, attorneys, and corporate and government officials to explore areas of interaction and improve communication among the science, engineering, and legal communities. This program is intended to provide a neutral, nonadversarial forum for promoting understanding, encouraging imaginative approaches to problem solving, and conducting studies.

In the Supreme Court, as a matter of course, we hear not only from the parties to a case but also from outside groups, which file 30-page amicus curiae briefs that help us to become more informed about the relevant science. In the “right-to-die” case, we received about 60 such documents from organizations of doctors, psychologists, nurses, hospice workers, and handicapped persons, among others. Many discussed pain control technology, thereby helping us to identify areas of technical consensus and disagreement. Such briefs help to educate the justices on potentially relevant technical matters, making us not experts but moderately educated laypersons, and that education improves the quality of our decisions.

Moreover, the Supreme Court recently made clear that the law imposes on trial judges the duty, with respect to scientific evidence, to become evidentiary gatekeepers. The judge, without interfering with the jury’s role as trier of fact, must determine whether purported scientific evidence is “reliable” and will “assist the trier of fact,” thereby keeping from juries testimony that is not respected by other scientists. Last term, the Supreme Court made clear that this requirement extends beyond scientific testimony to all forms of expert testimony. The purpose of Daubert’s gatekeeping requirement “is to make certain that an expert, whether basing testimony upon professional studies or personal experience, employs in the courtroom the same level of intellectual rigor that characterizes the practice of an expert in the relevant field.”

Federal trial judges, looking for ways to perform the gatekeeping function better, increasingly have used case-management techniques such as pretrial conferences to narrow the scientific issues in dispute, pretrial hearings where potential experts are subject to examination by the court, and the appointment of specially trained law clerks or scientific special masters. Judge Jack B. Weinstein of New York suggests that courts should sometimes “go beyond the experts proffered by the parties” and “appoint independent experts” as the Federal Rules of Evidence allow. Judge Gerald Rosen of Michigan appointed a University of Michigan Medical School professor to testify as an expert witness for the court, helping to determine the relevant facts in a case that challenged a Michigan law prohibiting partial-birth abortions. Judge Richard Stearns of Massachusetts, acting with the consent of the parties in a recent, highly technical, genetic engineering patent case, appointed a Harvard Medical School professor to serve “as a sounding board for the court to think through the scientific significance of the evidence” and to “assist the court in determining the validity of any scientific evidence, hypothesis or theory on which the experts base their testimony.”

The Supreme Court recently made clear that the law imposes on trial judges the duty, with respect to scientific evidence, to become evidentiary gatekeepers.

In what one observer describes as “the most comprehensive attempt to incorporate science, as scientists practice it, into law,” Judge Sam Pointer Jr. of Alabama recently appointed a “neutral science panel” of four scientists from different disciplines to prepare testimony on the scientific basis of the claims in the silicone gel breast implant product liability cases consolidated as part of a multidistrict litigation process. This proceeding will allow judges and jurors in numerous cases to consider videotaped testimony by a panel of prominent scientists. The use of such videotapes is likely to result in more consistent decisions across courts, as well as great savings of time and expense for the individual litigants and the courts.

These case-management techniques are neutral, in principle favoring neither plaintiffs nor defendants. When used, they have typically proved successful. Nonetheless, judges have not often invoked their rules-provided authority to appoint their own experts. They may hesitate simply because the process is unfamiliar or because the use of this kind of technique inevitably raises questions. Will the use of an independent expert in effect substitute that expert’s judgment for that of the court? Will it inappropriately deprive the parties of control over the presentation of the case? Will it improperly intrude on the proper function of the jury? Where is one to find a truly neutral expert? After all, different experts, in total honesty, often interpret the same data differently. Will the search for the expert create inordinate delay or significantly increase costs? Who will pay the expert? Judge William Acker Jr. of Alabama writes: “Unless and until there is a national register of experts on various subjects and a method by which they can be fairly compensated, the federal amateurs wearing black robes will have to overlook their new gatekeeping function lest they assume the intolerable burden of becoming experts themselves in every discipline known to the physical and social sciences, and some as yet unknown but sure to blossom.”

A number of scientific and professional organizations have come forward with proposals to aid the courts in finding skilled experts. The National Conference of Lawyers and Scientists, a joint committee of the American Association for the Advancement of Science and the Science and Technology Section of the American Bar Association, has developed a pilot project to test the feasibility of increased use of court-appointed experts in cases that present technical issues. The project will recruit a slate of candidates from science and professional organizations to serve as court-appointed experts in cases in which the court has determined that traditional means of clarifying issues under the adversarial system are unlikely to yield the information that is necessary for a reasoned and principled resolution of the disputed issues. The project also is developing educational materials that will be helpful to scientists who are unfamiliar with the legal system.

The Federal Judicial Center will examine a number of questions arising from such appointments, such as the following:

• How did the appointed experts perform their duties?
• How did the court, while protecting the interests of the lawyers and the parties they represent, protect the experts from unreasonable demands, say, on their time?
• How did the court prepare the experts to encounter what may be an unfamiliar and sometimes hostile legal environment?

The Private Adjudication Center at Duke University is establishing a registry of independent scientific and technical experts who are willing to provide advice to courts or serve as court-appointed experts. Registry services also are available to arbitrators and mediators and to parties and lawyers who together agree to engage an independent expert at the early stages of a dispute. The registry has recruited an initial group of experts in medicine and health-related disciplines, primarily from major academic institutions, and new registrants are added on a regular basis. As needed, the registry also conducts targeted searches to find experts with the qualifications required for particular cases. Registrants must adhere to a code of conduct designed to ensure confidence in their impartiality and integrity.

These projects have much to teach us about the ways in which courts can use such experts. We need to learn how to identify impartial experts. Also, we need to know how best to protect the interests of the parties and the experts when such extraordinary procedures are used. We also need to know how best to prepare a scientist for the occasionally hostile legal environment that arises during depositions and cross-examination.

It would undoubtedly be helpful to recommend methods for efficiently educating (that is, in a few hours) willing scientists in the ways of the courts, just as it would be helpful to develop training that might better equip judges to understand the ways of science and the ethical, as well as practical and legal, aspects of scientific testimony.

In this age of science, we must build legal foundations that are sound in science as well as in law. Scientists have offered their help. We in the legal community should accept that offer. We are in the process of doing so. The Federal Judicial Center’s new manual on science in the courtroom seeks to open legal institutional channels through which science—its learning, tools, and principles—may flow more easily and thereby better inform the law. The manual represents one part of a joint scientific-legal effort that will further the interests of truth and justice alike.