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The Age of Expert Testimony: Science in the Courtroom - Report of a Workshop 4 The Scientist’s Role in the Courtroom “Here’s the bottom line. When you ladies and gentlemen with your M.D.s and Ph.D.s come into a courtroom, you are going to be forced to use the court’s language, you are going to have to follow the court’s procedures. Or put a little differently, you’re going to be playing in my ballpark and by my rules. It will not be a scientific meeting where one presenter gets up after another with their power points and their overheads and presents their paper. They get a few questions and then you move on to the next person. It’s a very, very different situation.” — Judge Richard Levie Many scientists, engineers, and physicians are understandably reluctant to testify in court, and the workshop spent considerable time discussing this issue. From the point of view of the scientist, the courtroom is “someone else’s turf, where the rules are different and unfamiliar.” This situation, said one veteran scientific witness, “is a challenge that used to frighten me and continues to worry many of my colleagues as they consider whether to step into the courtroom.” Common concerns of scientists are that they will be embarrassed publicly, their results may be misunder-stood or used out of context, and that they may be branded as a “hired gun” for one side or another of an issue. One reason scientists are uncomfortable in the courtroom is that they are neither trained in nor comfortable with the formalism of the legal adversary proceeding as a mechanism to resolve scientific differences. One scientist discussed the modes of debate in science, which tradition-ally lead to consensus, not victory or defeat. When a group of scientists is
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The Age of Expert Testimony: Science in the Courtroom - Report of a Workshop asked to address a question, the group eventually recognizes the value of the strongest evidence and opinions. At that point, even if one or a few members of the group are at extreme ends of the bell-shaped curve of opinion, the custom is for all to join in a “consensus truth.” In the courtroom, the goal is not a consensus truth but a definitive decision. Although there may be a consensus in the scientific community about a particular question, this consensus is unlikely to appear in the courtroom. Instead, opposing attorneys search out experts from the tails of the bell-shaped curve so as to strengthen their particular arguments. Even so, some scientific, engineering, and medical experts feel a responsibility to make themselves available to offer courtroom testimony; some of whom go so far as to define a collective responsibility to do so. Their reasoning is that the best way to provide sound evidence for legal questions is to provide the most qualified experts. “If those of you who are honorable, conscientious, and learned don’t show up,” said a judge, “then who do you think will show up?” Another view presented was that both science and the law are human activities and, in certain respects, social constructs. It is not surprising that members of each group are unfamiliar with the culture and “professional myths” of the other. Participating in resolving legal disputes is one way for the two cultures to “untangle those myths” and learn to communicate better. In discussing ways to encourage the scientific community to improve expert testimony, participants discussed a role for professional societies and for programs of the AAAS and the National Academies. Some societies have, or are considering, codes of practice for this purpose. Other participants doubted that professional societies would have enough courtroom expertise to be helpful and might even, particularly for licensed professions, find difficulty in resolving definitions and issues of practice. THE PRACTICE OF SCIENCE In its Daubert opinion, the Court repeatedly uses the term “scientific method,” a concept discussed at length during the workshop. In general, the participants disliked the idea of a too-exact definition in regard to science. As one participant said, “There is no definition of ‘scientificity’.” As suggested previously, the hypotheses and knowledge of science are always evolving, and this includes the science that underlies scientific evidence. An hypothesis can be falsified or disproved, but it cannot be labeled “permanently true,” because the knowledge on which it is based is always incomplete. An hypothesis that is tested and found “not to be false” is considered to be corroborated but not proved. Indeed, the work of science is to test hypotheses. This process may
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The Age of Expert Testimony: Science in the Courtroom - Report of a Workshop begin with an observation about the world and proceed to the formula-tion of an hypothesis to explain that observation; this is followed by the performance of experiments and the collection of data to test the hypothesis, and finally by a lengthy process of peer review, publication, and attempts by other researchers to replicate the experiment. Out of this process grows consensus within the scientific community. As one brief filed in Daubert suggested, “Scientific methodology today is based on generating hypotheses and testing them to see if they can be falsified; indeed, this methodology is what distinguishes science from other fields of human inquiry.”13 This statement is followed in the Daubert opinion by a quote from Karl Popper, another eminent philosopher of science, who wrote in the 1930s: “[T]he criterion of the scientific status of the theory is its falsifiability or refutability or testability.”14 Chief Justice Rehnquist was sufficiently perplexed by this assertion to offer a mild dissent: “I defer to no one in my confidence in federal judges, but I’m at a loss to know what is meant when it is said that the scientific status of a theory depends on its falsifiability, and I expect some of them will be confused, too.15 Workshop participants found no problem with refutability, or test-ability. Scientific experiments are published publicly for the purpose of offering others the chance to replicate the results of the experiment and either to refute them or confirm them. They did discuss the notion of falsifiability at some length, however, as a concept that was produced by philosophers of science in the 1930s, 1940s, and 1950s, but which has been incorporated into more sophisticated conceptions of science today. GOOD SCIENCE, BAD SCIENCE, AND PSEUDO-SCIENCE Several participants discussed the common public perception that scientists sometimes offer bad or “pseudo” science as evidence in the courtroom. A scientist at the workshop emphasized several reasons for this perception. He said that at one extreme of an imaginary spectrum are the “hard” sciences, such as molecular biology, physics, and chemistry. At the other end of the spectrum are the “pseudo-sciences,” such as astrology and numerology. In the middle, he said, are many topics whose 13 Green, “Expert Witnesses and Sufficiency of Evidence in Toxic Substances Litigation: The Legacy of Agent Orange and Bendectin Litigation,” 86 Nw. U. L. Rev. 643 (1992), cited in Daubert amici curiae brief of Nicolaas Bloembergen et al. 14 K. Popper, “Conjectures and Refutations: The Growth of Scientific Knowledge,” 37 (5th ed. 1989). 15 Daubert, 61 U.S.L.W. at 4811.
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The Age of Expert Testimony: Science in the Courtroom - Report of a Workshop status is less clear, including acupuncture, handwriting analysis, and psychological profiling. The important point, he said, is that even the pseudo-sciences share features with the harder sciences, but they do not have “enough of the virtues, such as refutability,” to elevate them to the status of science. Conversely, even some of the hardest sciences lack some aspects of “scientificity.” Quantum mechanics, for example, contains elements that are not testable, intuitive, or conservative. The important point is that there is no crisp distinction or algorithm that divides science, almost-science, and pseudo-science. “The difficulty of trying to tell science from pseudo-science, or real science from unreal science,” said the scientist, “is not a problem to be solved. It’s a problem to be gotten over. As the software people say, ‘It’s not a bug, it’s a feature’.” Because scientific areas have different standards for assessing evidence, experts can in good faith disagree over interpretations of data and other evidence. Even though scientists strive for consensus, every respected scientific journal reflects the lively debates that precede consensus. In court, two competent and ethical scientists may disagree in good faith, and such disagreements should not be taken as a sign that bad science is being practiced or that science has failed. Freedom to disagree should be seen as a strength, not a weakness, of science. Participants also discussed the “huge variation” among the cultures of large scientific communities that may cause confusion in the courtroom. For example, epidemiologists, who deal with probabilities rather than certainties, tend to speak with restraint; pathologists, whose task is to define a particular mechanism of disease or cause, are more willing to draw conclusions. ASSESSING RISK One of the hardest jobs scientists are asked to do—in the courtroom or in the laboratory—is to assess the risk to humans of certain chemicals or other agents. The workshop was attended by experts in both epidemiology and toxicology, two fields in which experts are commonly asked to provide evidence of risk. The task of risk assessment is often complicated by conflicting evidence from experts in these two fields. For example, an epidemiological study of 300,000 petroleum workers showed that the chemical benzene is not associated with non-Hodgkin’s lymphoma. However, the toxicological literature, describing workers in China exposed to higher levels of benzene, provides evidence of chromosomal abnormalities that are specific for non-Hodgkins lymphoma. In addition, benzene can cause non-
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The Age of Expert Testimony: Science in the Courtroom - Report of a Workshop Hodgkin’s lymphoma in laboratory animals. Is benzene, therefore, toxic or benign? Is its toxicity a matter of the exposure level? Another source of confusion is the limits of epidemiology, in which inferences are applied to populations of persons, not individuals. It is possible to say that cigarette smoking increases the likelihood of lung cancer in large populations, for example, but virtually impossible to say with certainty from epidemiological studies alone whether a particular individual’s cancer was caused by smoking. An epidemiological study is said to be sound when its conclusions meet certain generally accepted criteria. Among these are: Consistency: Not just one population, but several populations should show an elevated risk of illness from exposure. Strength of association: Stronger associations are more likely to have a causal explanation, because potential biases are less likely to cause the association. Temporality: Exposure must precede effect. Plausibility: Is a cause plausibly linked with an effect? Is the evidence consistent with the larger body of scientific knowledge that pertains to the topic? Is there a biological mechanism that explains how the changes take place? Epidemiologists prefer to see their evidence confirmed by all of these criteria, as well as some of the additional Bradford Hill criteria16 (such as dose response, specificity of the association, and replication). Their application, however, is a matter of judgment, where differences can easily arise. RELATIVE RISK One concept that causes confusion in the courtroom is that of relative risk. Here again, the scientist’s cautious search for consensus often con-flicts with the litigant’s need for a prompt decision regarding an indi-vidual dispute. For example, some courts have adopted a policy that a relative risk greater than 2.0 must be shown to establish causality.17 That is, the court 16 Bradford-Hill, A., ”The Environment and Disease: Association or Causation?” Proc. Royal Soc. Med. 58:295 (1966); see also: Bradford-Hill, A., “The Environment and Disease: Association or Causation?” President’s Address. Proc. Royal Soc. Med. 9:295-300 (1965). 17 By definition, an agent that creates a health risk of 2.0 is said to double the risk. Similarly, an agent that creates a health risk of 1.2 is said to increase a risk by 20 percent; and so on.
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The Age of Expert Testimony: Science in the Courtroom - Report of a Workshop does not deem an agent or condition that is associated with a risk of less than 2.0 to be more likely than not the cause of an individual’s injury, even though there is evidence that the agent or condition does increase the risk. Some courts use the same standard for admissibility of evidence. Consequently, in these courts unless an agent is associated with a relative risk greater that 2.0, the expert will not be permitted to testify about the possibility that the agent causes the illness or harm. One speaker noted that the use of such “bright lines” is troubling to scientists for several reasons: There is no biological reason for the use of a 2.0 standard as opposed to any other standard. The use of such a hard standard obscures the fact that any risk means that some people could be harmed by the agent in question. For example, the relative risk of “passive” smoking—a person who never smoked but lives in proximity to smokers—is reliably shown to be about 1.2, i.e., the risk of developing lung cancer is elevated about 20 percent by passive smoking. A court using the standard of 2.0 would not admit evidence about passive smoking, and a group of people who have contracted lung cancer from passive smoking would not be able to seek compensation. In terms of verdicts, the plaintiff will lose every case and will collect nothing where the relative risk is 1.2, while the defendant will lose every case and will pay everyone where the relative risk is 2.2. The use of a bright line may confuse risk with incidence. Relative risk is the likelihood of the occurrence of a harmful effect, given certain assumptions about the frequency, duration, and magnitude of exposure. Public health authorities, however, usually consider the calculated incidence or frequency of an effect. For example, if a chemical is calculated to carry a risk at a rate of only one in 10,000, and only 10 people are exposed, there is no real expectation of an actual incidence of the effect. Participants discussed several other points that may complicate court decisions. First, while the process of litigation may seek to assign risk to a single cause, most diseases are multi-factorial. Similarly, the “laws” of toxicology may be unclear to juries. For example, an overriding principle of toxicology is that the “dose makes the poison”; virtually everything can be toxic if taken in sufficient quantity. In addition, juries may not understand the concept of specificity. That is, each chemical may have a very specific effect that depends on its molecular structure; simply moving or exchanging a single atom may alter the effect of a substance. These scien-
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The Age of Expert Testimony: Science in the Courtroom - Report of a Workshop tific laws are easy to confuse, for example, when considering the toxicity of a substance, because the dosage of a toxic agent required to produce a particular disease in an animal may be far higher than the exposure of humans who are working with the toxic agent. ASSESSING CAUSATION IN SPECIFIC INDIVIDUALS The search for “truth” in the courtroom may become problematic when causative questions move beyond hard science to behavioral or philosophic realms. Physicians, in particular, are commonly asked to comment on issues that are “outside the box of scientific rigor,” as one speaker said. At the bedside and in the clinic, diagnosis of signs and symptoms is done with a variety of therapeutic ends in mind. The first goal is to ame-liorate suffering and disability. Intervention can include the treatment of the disease, the repair of injury, or the reduction or elimination of envi-ronmental causes of illness. A second goal is to comfort patients and their families. Here, the speaker stated, diagnosis is done largely for purposes of explanation—“as a narrative to hold on to.” In the courtroom, the goal of diagnosis is to identify a cause of a condition for purposes of ascribing responsibility to people and institutions. Yet the legal system’s desire to answer questions of responsibility and accountability frequently forces non-therapeutic questions on physicians. In child custody cases, for example, a physician may be asked which parent is “better” for the child, even when neither carries a disabling clinical diagnosis. Criminal law moves even farther from clinical matters into questions of personal responsibility and moral or existential questions. Physicians (as well as psychiatrists and psychologists) may be asked to comment on the level of criminal intent, competency to stand trial, or the appropriate-ness of a death sentence, all of which are distant from the physician’s familiar terrain of clinical diagnosis. Remarkably, said one attorney, the scrutiny of medical experts speci-fied by Daubert is rare. “When medical necessity is at stake in health insurance coverage cases,” he said, “the plaintiffs’ and the managed-care organizations’ experts are almost always allowed in.” Similarly, when the insanity defense is at issue in criminal cases, clinical experts are permitted to opine not merely about psychiatric diagnosis and symptoms but also about perceived responsibility of the examined individual—“without Daubert or Kumho standing in the way.”
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