A toxic tort, as the term is used in this Article, is a cause of action that arises when a plaintiff has developed a disease following long-term exposure to a physical agent—either a chemical or a form of energy such as electromagnetic fields (EMFs). Typically, the defendant’s economic activity resulted in the plaintiff’s exposure to the agent. Courts essentially must determine whether the plaintiff’s exposure and subsequent disease are causally related, as that relationship is defined by the applicable law, or whether the exposure and disease are associated merely by chance. For example, did the asbestos inhaled by the plaintiff cause his1 lung cancer? Did the radar gun used by the traffic control officer cause his testicular cancer? Did the Bendectin taken by the plaintiff cause the birth defects that occurred thereafter? Traumatic injury occurs instantaneously, but disease develops over a period of time. The cause of disease, therefore, cannot be the direct object of the senses and can only be inferred.
It is possible to imagine a legal system in which the absence of direct observation of the genesis of disease would constitute an absolute bar to a plaintiff’s recovery. Although such a system may have merit, it is not the law in American courts. Rather, under appropriate safeguards, a scientific expertise permitted to offer an opinion2 concerning the ultimate issue; whether the defendant’s economic activity caused the plaintiff’s disease.
This Article examines the valid use of expert testimony with respect to causal knowledge in furtherance of justice. The expert may employ the causal concepts of science when expressing purely scientific knowledge. Indeed, it is the layman’s lack of such specialized knowledge that is the fundamental justification for the law’s use of expert testimony. Ultimately, however, application of the principle of causality remains the exclusive province of the trier of fact because the law employs the layman’s concept of causality for the resolution of causal issues.3
This Article is solely concerned with causality in the context of harm that manifests after a period of time has elapsed from the subject’s initial contact with the putative causal agent. This situation presents the most troubling and complex issues regarding the determination of causal relationships using scientific knowledge. Excluded from consideration is the Bhopal-type disaster, in which a chemical escapes from a broken pipeline and causes almost immediate death.4 Although, in such a disaster causality is a necessary element in a subsequent cause of action, causality is not likely to be its most important element.
For convenience, this Article assumes the underlying legal theory in a toxic tort case is ordinary negligence.5 Thus, the plaintiff has the responsibility of pleading and proving the toxic agent proximately caused the plaintiff’s disease or injury. The concept of proximate causality consists of “legal causation” and “causation-in-fact.”6 Legal causation involves issues of foreseeability, duty, and policy. Ordinarily, legal causation is not a pivotal issue in toxic tort cases because a defendant’s breach of the duty not to cause cancer or other disease necessarily leads to a finding of legal causation. Thus, in a toxic tort case, proof of causation-in-fact is tantamount to satisfying the element of proximate causality. This Article, therefore, will focus on issues involving causation-in-fact, rather than legal causation.7
The decision to undertake this Article was prompted in part by our perception that much of the legal scholarship dealing with the relation of science and law is unenlightening and circular because of failure to define terms, employ them consistently, and give examples to aid in the understanding of general statements. We have attempted to avoid these perceived shortcomings by providing definitions throughout the Article and in the Glossary, and by the liberal use of examples. Most of the examples and hypotheticals involving scientific matters and legal issues used in this article are based on the personal experiences of Andrew A. Marino. Citations to the original materials are given when further details might be helpful in understanding the matter being discussed.
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II. CAUSALITY IN SCIENCE
In a toxic tort case, the expert is not required or expected to have knowledge regarding the law or legal concepts, or to take them into account when testifying. Thus, “proximate cause,” “legal cause,” “foreseeability,” “duty,” and other legal terms of art are not pertinent to an expert’s testimony. Rather, the expert’s testimony is confined to the area of human knowledge called science. In its broadest conceptualization, science consists of making valid observations, inferring reasons for the observations, and offering mechanistic explanations; success in this endeavor is measured by the resulting ability to predict future events. In principle, science is independent of the values of the practicing scientist; this ideal characteristic distinguishes science from law, and from other human activities such as philosophy, theology, and art. In contrast to mathematics, which is axiomatic and seeks reasons based on logic, science is observational and seeks reasons based on experience.
Scientific knowledge is based on observations made within a philosophical and procedural framework.8 The applicability of scientific knowledge outside that framework depends on whether scientific knowledge extends to society at large, where the underlying philosophy is not always logical empiricism, value and policy have a recognized role, and the existence of a causal relationship is proved differently. If a particular scientific inference cannot be extended from science to society, scientific knowledge has no utility in a toxic tort case.9
It is a daunting task to formulate rules within which the potential societal significance of scientific knowledge can be recognized and evaluated. One of the barriers to such an effort is the traditional absence of scientific training in the formal education and practical experience of judges and lawyers. Nevertheless, the cost and importance of scientific knowledge are so great that such rules must be developed.
It is intuitively clear that an effort to incorporate scientific knowledge into the legal system must begin with an appreciation of what a scientist means by stating “x caused y.” The meaning of such a statement depends on whether the putative relationship involves living or nonliving things.10
The physical sciences (physics and chemistry, for example) involve the study of nonliving things, such as an atom of hydrogen, a beam of light, or the planet Jupiter. An entity called force11 is postulated to be the necessary and sufficient cause for every event (also called an observation, effect, or phenomenon). Thus, “x caused y” means that “x” was the set of forces that was necessary and sufficient for “y” to happen.12
The biological sciences (biology and physiology, for example) involve the study of animals and plants. The complexity of living organisms is such that myriad factors can affect them, and any such factor is labeled a cause. Thus, “x caused y” means that “y” would not have occurred under the circumstances as and when it did but for the presence of “x.” For example, consider the relationship between smoking and cancer. Smoking is not always a sufficient cause of cancer because not everyone who smokes a similar amount for a similar time period develops cancer. Moreover, it is not a necessary cause because not everyone who develops cancer has a history of smoking. But the scientific evidence shows that cancer occurs more often among those who smoke. It follows, therefore, that among smokers who developed cancer, smoking was sufficient in the circumstances to cause cancer in some instances. That is, smoking was a sufficient cause in some cases.
The essential meaning of cause in biological sciences, that of a factor sufficient in the circumstances to modify a subsequent event, is essentially identical to its lay meaning. For example, “the cause of death was a gunshot wound” means that the death would not have occurred when, where, and to whom it occurred but for the wound. The wound was not necessary for the victim to die, and in other circumstances may not have been sufficient to result in death. The wound was simply sufficient in the circumstances to cause death.13
In toxic tort cases, it is important to distinguish between causes and mechanisms. For example, it can be inferred from valid observations that consumption of aspirin causes headaches to abate, or that living beside high-voltage powerlines causes cancer, but the validity of each of these causal conclusions is independent of knowledge of the underlying mechanical causes. That is, the particular cellular location at which aspirin acts, and the signal transduction and gene expression caused by EMF’s need not be understood prior to, or as part of, the process by which the validity of the causal relationship is evaluated. Since the mechanistic causes of few biological phenomena—and no putative toxic torts—are known with reasonable precision, there cannot be a toxic tort cause of action if the element of proximate causality is interpreted to require proof of mechanistic causes.14
A. Generalization in Science: From Caused to Can Cause
In an experiment involving laboratory rats and asbestos, suppose “x” was a specific amount of asbestos per cubic meter of air in the room that housed a particular gender and strain of rats (e.g., ten micrograms/cubic meter, and Sprague-Dawley males), “y” was the observation of cancer at a particular rate (e.g., twenty percent), and “x caused y” was justified in the experiment by means of a statistical test. Clearly, if “x caused y” is true,15 it follows that “x can cause y” is also true.
Suppose that we contemplate the meaning of “x can cause y” where “x” now represents a higher concentration of asbestos particles than was used in the actual experiment. The conclusion that “x can cause y” was originally rationalized by reference to the observation that “x caused y,” but it is incorrect to say “caused” at the higher concentration because that experiment has not been performed. If it were performed, the observed cancer rate might be different. In fact, for any “x” other than that used in the study, “x can cause y” would be untrue because the statement is specifically applicable to a particular “x” and “y,” and not based on the results of an experiment.
How, then, are the results of studies generalized so that the results may be used to state a proposition applicable in situations other than the precise circumstances of the original study? Such an inductive conclusion is justified when a sufficient number of additional studies yield mutually consistent results. The induction may then be expressed by removing the terms qualifying the subject and the predicate. The result is that the assertion becomes “X can cause Y,” where “X” is asbestos,16 and “Y” is cancer.17 Thus, reasoning in biology proceeds from a group of specific observations to an inductive statement, the generality and applicability of which depends completely on the quality, quantity, and degree of relevance of the component studies.
In biology, the induction is expressed in words rather than in a precise mathematical expression as in physics. Hence, scientists’ views of the truth of an inductive biological judgment will differ just as individuals’ views regarding the importance of various items of evidence used to justify a judgment will differ.18 One factor affecting differing views is the scientist’s choice of scientific reports considered. Another factor is the weight the scientist affords particular studies. Perhaps the most important factor is the degree of certitude a scientist implicitly incorporates in his inductive generalization. Some scientists instinctively demand many studies and a high degree of certitude, while others find a general cause-and-effect relationship on the basis of only a few studies. If the meanest scientific data led a scientist to posit a causal link, or if the strongest possible data did not do so, the scientist would not be a proper expert witness because the scientist would no longer be acting as a scientist, but as an advocate. It is the responsibility of counsel to expose the expert’s personal standards so that the trier of fact can appropriately judge the scientist’s reasoning process.19
B. Can’t Cause in Science
In a toxic tort case, the plaintiff must prove that the toxic agent caused the disease. The thrust of the defendant’s evidence will attempt to illustrate that such a causal inference is not warranted.20 Alternatively, the defendant may attempt to affirmatively establish that the toxic agent can’t cause the plaintiffs type of disease. For example, if a defendant in an asbestos case could prove that asbestos cannot cause cancer, it would be unnecessary to consider the actual dose the plaintiff received because the safety of asbestos under all reasonable circumstances would have been established.
Consider, for example, an attempt to rationalize the statement “asbestos can’t cause cancer.” Such an undertaking would consist of a series of animal experiments in which various doses were applied under specific conditions, and the resulting incidence of cancer was determined. If a range of doses was tested and increased cancer was not observed, then it would be true to say that no evidence favoring “asbestos can cause cancer” was found. Expressed in other language, a valid inference would be that “asbestos can’t cause cancer” in the circumstances of the studies. Cannot, therefore, tentatively might be inferred from a series of did not observations. The negative inference becomes a nullity, however, when even one animal study is positive. If the results were uniformly negative when the study was repeated using ten different asbestos doses, and the eleventh study was positive, it would no longer be true to infer that asbestos cannot cause cancer. Thus, one valid affirmative study may destroy a plausible inference that was based on numerous valid negative observations.21
An affirmative defense of can’t cause, therefore, is nearly impossible from a scientific viewpoint because a null hypothesis can be disproved, but it cannot be proved. Furthermore, such a defense is usually strategically unwise because it may be perceived as an attempt to prove too much. A defendant should rarely prevail in a toxic tort suit on the basis of a can’t cause affirmative defense because there are few, if any, commercially significant physical agents for which there are no relevant well-conducted positive studies.
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III. QUALIFICATIONS OF THE EXPERT IN TOXIC TORTS
An expert is a person who has knowledge not ordinarily possessed by the layman. Historically, the courts have permitted experts to testify when specialized knowledge is relevant to an issue in a case. If a court agrees that expert testimony is needed, the court determines the specialty or profession that encompasses the required expertise and whether the witness has the requisite training and experience.22
In a toxic tort case, the gist of the expert’ s testimony is a causal assertion such as: “the asbestos caused …,” “the Bendectin caused …,” or “the electromagnetic field caused….” The toxic tort expert, therefore, must have training and experience sufficient to analyze and explain the laboratory and epidemiological studies pertinent to the effects of the toxic agent at issue on animals and human beings. The expert must sufficiently understand the studies that have been conducted in order to ascertain whether the data and conclusions are valid, and if so, how the data and conclusions apply to the facts of the case. Evidence of this ability consists of documented academic attainment and a demonstrated history of adducing and evaluating scientific data, ideally including data involving the toxic agent pertinent to the case. No expert should be permitted to testify regarding causality if the expert lacks academic attainment and actual experience of the appropriate type, and few experts should be permitted to testify if they possess only one such qualification.23 If the witness was trained appropriately, performed many experiments, and published many scientific articles dealing with the biological effects of the toxic agent involved in the case, the court would have a firm basis to regard the witness as qualified to offer opinions in the case.
A reasonable approach to matching the expert’s knowledge to a particular case is to inquire whether the causal issue—which must be framed in the pleadings since it is an element of the cause of action—is within the training and experience of the proffered expert. First, does the expert’s academic background indicate training in the scientific methods and processes for inferring causality? An earned Ph.D. in any science indicates that the witness satisfies this requirement, although other evidence such as actual experience may suffice. Second, has the witness demonstrated a familiarity with the scientific studies that embody the current scientific knowledge regarding the effects on living organisms produced by the toxin of interest? The best such evidence would consist of scientific publications or other suitable written reports authored by the expert and dealing with the issue of the biological effects of the toxic agent. If the expert possesses these two characteristics, the causal issue should be within the training and experience of the expert.
B. Non-Causal Knowledge
The relationship between the amount of exposure to the toxic agent experienced by subjects in particular scientific studies and the amount of the plaintiff’s exposure is always an important consideration in deciding whether the toxic agent caused the plaintiff’s disease. For example, if the amount of asbestos the plaintiff breathed was infinitesimally small compared with the amount shown to cause adverse effects in laboratory animals or associated with cancer in human observational studies, there would be no reasonable basis for an expert to assert the likelihood of a cause-and-effect relationship between the plaintiff’s dose and the plaintiff’s disease.
Scientific studies conducted under laboratory conditions usually describe the amount of the agent used in the study. This is rarely the case with epidemiological studies because epidemiological studies are usually retrospective in nature and therefore involve an analysis of events that existed prior to the design and conduct of the study. This situation necessarily precludes measurement by the investigator of the levels of the toxic agent actually experienced by the epidemiological study subjects.24 The fact of exposure is determined based on place of residence or occupation, but the actual exposure levels can only be estimated, using situations similar to those that existed during the study. For example, individuals living beside a high-voltage powerline or airport radar, working as electrical engineers, or operating ham radios were regarded as being exposed to electromagnetic fields,25 but the specific levels of the electromagnetic fields involved were not stated in the published studies.
The expert must know and understand the scientific laws and principles that apply to movement or propagation of the toxic agent in the environment and in the body. The expert must demonstrate that he is qualified to make relative evaluations of the exposure levels or doses used in laboratory studies, the dose of toxin experienced by the subjects in the epidemiological studies, and the dose experienced by the plaintiff.
Knowledge of dosimetry26 is distinct from knowledge of scientific causality. For example, suppose that Dr. Able, Chairman of the Department of Epidemiology at State University and author of several published studies involving the biological effects of asbestos, offers to testify that the plaintiff’s disease was caused by occupational exposure to asbestos fibers. Since studies have shown that asbestos workers exhibit higher than expected cancer rates, it is reasonable to conclude that asbestos can cause cancer. Dr. Able, therefore, is qualified to testify to that effect. It does not necessarily follow, however, that Dr. Able is qualified to testify that asbestos caused the plaintiff’s cancer unless Dr. Able can also evaluate the levels of asbestos experienced by the subjects in the published studies in relation to the exposure levels experienced by the plaintiff.
The ability to analyze technical reports to determine whether measurements were made properly, and to infer exposure levels from descriptions of conditions attendant to the plaintiff’s exposure, cannot necessarily be inferred from the demonstration that Dr. Able is an expert in the epidemiology of asbestos. In Dr. Able’s published studies, for example, the technical expertise regarding dosimetry of asbestos may have been the responsibility of one of his co-authors. It is proper for such a community of expertise to be formed in the context of a scientific publication.27 In the courtroom, however, Dr. Able must explain and defend any assertion that the plaintiff’s dose of asbestos was comparable to the levels that occurred in his published studies. Absent specific indications in Dr. Able’s background that he has the qualifications to analyze technical reports regarding measurements of asbestos levels under various conditions applicable to the plaintiff’s situation, Dr. Able is not qualified to opine regarding the specific cause-and-effect relationships involving the plaintiff. Knowledge of dosimetry is an essential element in the expert’s causal conclusion. The issue of dosimetry, therefore, cannot properly be framed as a hypothetical, with supporting evidence supplied by another expert.
If Dr. Able had no training or experience in evaluating animal experiments, Dr. Able would be incompetent to distill information from animal studies that might be crucial to the issue of dosimetry.28 For example, suppose animal studies showed that asbestos breathed by animals was rapidly removed from the lungs by the lymphatic system so that actual levels of asbestos did not build up in lung tissue until the level of airborne asbestos was above a specific amount. Such information is pertinent because it tends to establish a threshold below which adverse consequences from asbestos would not occur since the asbestos was rapidly removed from lung tissue and hence not present to cause any adverse effects. Without such knowledge, therefore, Dr. Able would be incompetent to testify regarding the specific cause-and-effect relationship.
C. Scientific and Medical Experts Distinguished
Physicians make causal inferences in different ways and for different purposes than do scientists.29 Although the training of Ph.D.s and M.D.s in the biological sciences are similar in both college and the first two post-graduate years, the pathways diverge thereafter, as is necessary for the acquisition of skill in two fundamentally different areas of human knowledge. The three to five year training period in the methods of science, which is an integral part of the education of the Ph.D. student, has no counterpart in the education of the physician. Consequently, even though a physician may actually possess scientific knowledge, a physician is not necessarily an expert in the process of inferring causality from scientific data to the degree required to qualify as a courtroom expert. A physician has a received view of science and is charged with its implementation on behalf of his patients, not with the evaluation or expansion of that received view. It would be no more reasonable to presume that a physician was an expert in the process of scientific inference than it would be to expect a scientist to diagnose and treat disease.30
Both diagnosis and treatment of disease involve scientific and causal considerations, but they differ fundamentally from those based directly on data from scientific studies. The physician seeks to ascertain the cause of a patient’s symptoms, but within the framework of the physiology of the patient—for example, whether high blood pressure caused the dizzy spells, whether altered electrical activity in the brain caused the seizures, or whether the presence of a tumor caused the pneumonia. Determination of the cause of the high blood pressure, altered electrical activity, or tumor that, in turn, caused the patient’s symptoms generally is not within the training or the interest of the physician.31
In a medical malpractice case, expert testimony is required to establish both the duty of the defendant physician toward the plaintiff, and the role of the physician’s breach of that duty in causing the plaintiff’s injury. If the plaintiff offered testimony from a licensed physician having a Board certification in the medical specialty involved in the case, the physician would likely be permitted to opine regarding any medical issue in the case, including the question of causality. In essence, qualification as a medical expert is based on the physician’s status, as certified by the relevant state or professional accrediting agency. If accepted, the expert may testify regarding causality on the basis of the expert’s experience as a physician and his treatment of many patients with medical problems similar to those of the plaintiff. This form of expert reasoning is based on anecdotal knowledge, which may or may not be based on scientific knowledge. Such testimony, therefore, cannot serve as a substitute for the scientific reasoning the plaintiff must provide to sustain his case in toxic tort.
In a medical malpractice case, there are many potential expert witnesses. In toxic tort cases, however, where scientific rather than anecdotal knowledge must form the basis of the expert testimony, there will usually be only a few persons who possess the requisite knowledge.32 When courts fail to recognize the causal issue in toxic torts is distinct and different from that in medical malpractice, the typical result is acceptance of medical credentials in the context of disputes over scientific issues.33
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IV. VALIDITY OF SCIENTIFIC KNOWLEDGE
A. Intrinsic Validity
An expert’s opinion depends on the supporting data. The validity of the scientific studies and reports used by a qualified expert in toxic tort cases, therefore, should be an important consideration for the expert, the court, counsel, and the trier of fact. Scientists have long recognized the need for a process by which the validity of scientific data can be assessed. The process that developed to meet this need is one of the most important and pervasive features of science—peer review.
The peer review process may vary among different scientific specialties, but the process’ essential features are universal. After an experiment is conducted and evaluated, the investigator submits a written description of the work to a scientific journal that specializes in reviewing, evaluating, and publishing such research. The editor of the journal sends copies to persons the editor deems to be knowledgeable regarding the subject of the study.34
The reviewers, whose identities are not disclosed to the authors, comment on the scientific merit of the work described in the manuscript, including the following: the adequacy of experimental design; the appropriateness of statistical analysis; methods, and procedures used for handling animals or other research subjects; and the relationship among the stated aims of the study, the data obtained, the interpretation given, and the conclusions stated.
The reviewers do not consider either the method by which the study was funded or the ultimate reason it was performed when evaluating the merits of a particular report.35 Since the method of funding a study is not a factor in the review process, authors do not disclose funding to journal editors unless the authors choose to do so, or unless the funding source expects or requires disclosure.36
The reviewers provide a written evaluation covering the pertinent points of the manuscript, and the editor either accepts or rejects the manuscript, or accepts it conditionally. The latter decision is a recognition that the work merits publication, but only after comments raised by the reviewers have been adequately addressed. If the revised manuscript is deemed acceptable by the editor, the work appears in the journal in due course and becomes a permanent addition to the corpus of science, since journals are maintained in perpetuity in archival scientific libraries. Such a manuscript is said to have been peer reviewed, meaning the work has met a minimum standard within the particular scientific discipline regarding the quality of the work described therein, as determined by the journal editor.37
The peer-review process confers no express or implied warranties regarding the truthfulness, importance, or general acceptance of the methods or data in the report.3838 Nevertheless, the peer-review process serves its intended purposes of screening for obvious errors in methodology and reasoning and ensuring the work is not simply a rehash of previously performed work. Peer-reviewed studies are the means by which scientific knowledge is normally disseminated, learned, opposed, improved, corrected, or rejected. Consequently, peer-reviewed studies constitute and embody the knowledge that the expert in toxic torts should ordinarily use to perform analyses and reach conclusions. The peer-reviewed reports could be used, attacked, or reanalyzed to make inferences warranted by the data, but not made by the original authors. In each instance, however, it is the peer-reviewed publication39 that experts normally look to as the source of scientific knowledge, and therefore as the basis of scientific judgments.40
B. Extrinsic Validity
The source of funding of a scientific experiment is not a factor in the peer review of a manuscript because the review process is limited to scientific considerations. Nevertheless, the nature of the privity between the author of a scientific study and a party in a toxic tort case can affect the weight that should be accorded the study.41 Suppose an employee of a defendant power company published a study that concluded that living near powerlines does not result in increased risk of disease. It would be reasonable for the expert relying on this study, as well as the court and the trier of fact, to be aware that an employee of a party to the dispute performed the study. Even though the employee-employer relationship does not affect the peer evaluation, ordinary human experience suggests that such studies might be biased in some manner, and the relationship may properly serve as a basis for giving less weight to the results of the study. Thus, depending on a study’s funding, a question concerning its extrinsic validity may arise.
A contract is a method of funding research to provide knowledge desired by the funding party. Data obtained pursuant to a contract is owned by the funder, which therefore has the right to determine the data’s disposition and the extent of access that will be permitted.42 A typical investigator performing contract research is an employee of a private research organization or national laboratory.43 Investigators working under contract may be permitted to submit some of their work for peer review, depending on the sponsor’s needs and desires and the policy of the scientist’s organization. The sponsor, however, may have concerns regarding patentability, competitor advantage, or potential liability that may encourage secrecy regarding some or all of the study results. The lack of academic freedom to publish any data one chooses is a well-understood aspect of contract research. Tn agreeing to perform contract research, an investigator acknowledges that the primary goal is the satisfaction of the contract, not contribution to the corpus of public knowledge in science.
Another way of funding scientific research is the grant, a method whereby the goals of the research are chosen by the investigator, and the primary interest of the granting organization is the contribution to public knowledge within the particular branch of science.44 Under a grant, data produced in the experiment is ordinarily subject to the exclusive control of the investigator. At the investigator’s discretion, data is submitted for peer review and published in scientific journals. The typical grantee45 is an academician who is expected to perform research and publish as a condition of academic employment.
Although the idea of dishonesty in science in any form and to any degree is repugnant, various species of dishonesty do occur. An expert witness who relies on particular scientific reports, therefore, has a responsibility to consider the reports’ extrinsic validity, particularly its source of funding.
C. Reliance on the Work Product of Blue-Ribbon Committees46
Opinions concerning scientific matters pertinent to toxic tort litigation are sometimes provided by a blue-ribbon committee, a group of scientists appointed by a public or private organization with an interest in the analysis of a particular scientific issue that impacts society.47 Several factors indicate that the work product of blue-ribbon committees is not a reliable source of knowledge for an expert witness. First, the primary goal of a blue-ribbon committee is to arrive at a consensus, while the primary goal of an expert witness is to convey knowledge to the court in a truthful and accurate manner. Since there is no necessary connection between the consensus of a committee and the accuracy of its work product, an expert generally has no reason to accept a blue-ribbon committee’s consensus as accurate.
Second, a blue-ribbon committee’s consensus has no practical value unless it is formed by a representative group of individuals. Only then would it be reasonable to regard the committee’s opinion as an accurate characterization of the state of the pertinent science. If the forming organization chosen committee members because of their opinions, an expert witness would have no basis for according the committee’s opinion more weight than the members’ individual opinions.48
Third, the qualifications of the blue-ribbon committee members must be established before an expert may reasonably rely on the committee’s opinion. But an expert witness will frequently lack personal knowledge regarding the expertise of at least some committee members, and will therefore lack a basis to assess their qualifications to offer such an opinion. Even if the witness believed that all members were qualified, a question arises concerning the extent of time and effort actually expended by each member during committee deliberations.
Fourth, because blue-ribbon committees are formed by organizations with an interest in the results, blue-ribbon committees often have obvious conflicts of interest, and an expert would be naive to ignore them.49 Conflicts of interest occur even when a blue-ribbon committee is appointed by a federal50 or state51 agency. Over-arching governmental involvement in blue-ribbon committee selection, therefore, is not a substitute for choosing a balanced committee as a condition precedent to the representational validity of the committee’s opinion.52
The expert in a toxic tort case must recognize the work product of a blue-ribbon committee is unavoidably shaped by the appointing authority through its choice of committee members. If the expert lacks knowledge of the qualifications and extent of effort of the committee members, he has no rational basis for accepting their opinion. An expert should suspect conflicts of interest whenever the results of a blue-ribbon committee are dispositive of a scientific issue in a toxic tort suit, because such issues are often controversial and incapable of resolution on a purely scientific basis. While an expert witness is necessarily confined to-the scientific facts, value and policy considerations are usually incorporated into the opinion of a blue-ribbon committee. For these reasons, the expert should refrain from substituting a blue-ribbon committee’s judgment for his own. If the witness must rely on the work of a blue-ribbon committee, he is probably not an expert.
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V. APPLICATION OF SCIENTIFIC REASONING IN TOXIC TORT CASES
The expert in a toxic tort case must rationalize an assertion that the plaintiff’s disease and the dosage of the toxin received were causally related and not merely a chance association. For example, in the case of a traffic-control officer who used a radar gun and developed cancer, the plaintiff’s exposure to electromagnetic fields and his disease occurred in the context of many factors, among others: the plaintiff ate peanuts; smoked cigarettes; wore blue socks; drove a motorcycle; lifted weights; collected coins; lived near a superhighway; and had arthritic knees. The question arises, therefore, why the expert singled out electromagnetic fields as the causative agent, as opposed to myriad other co-existing circumstances.53
If the expert is to rationalize the causal relationship, the rationalization must be done on the basis of scientific knowledge, namely, an appropriate and reliable corpus of scientific data that permits the expert to infer that the plaintiff’s disease was a consequence of exposure to the toxic agent. Scientific studies potentially available regarding the question of causality are test-tube, animals and epidemiological studies, and each has particular strengths and weaknesses.54 Moreover, the methodology by which the scientific data is analyzed must itself be appropriate and reliable.
Although the expert must always consider the limitations of scientific studies with regard to inferring causal relationships in human subjects, such data are appropriately used to form causal inferences in proper situations. Animal and human studies are routinely used in science for this purpose. Indeed, most human and animal studies are performed with the intent to make such inferences. Causal inferences must be proved or disproved using such data before a drug can legally be advertised, an additive can be incorporated into a food product, a pesticide can be sprayed into the environment, or a powerline, nuclear power plant, microwave tower, or other facility that will emit potentially toxic agents into the environment can lawfully be constructed.55 It is quite clear, therefore, that the expert’s use of scientific studies to rationalize causal links in toxic torts is identical to the use of such data in myriad other areas.
A. Principal Inductive Opinion
The logic of scientific reasoning constrains the order in which the expert must approach a determination of whether the plaintiff’s exposure and the subsequent disease were causally related. Since the plaintiff was exposed to the toxic agent and developed a disease, the expert must first determine whether the toxic agent caused the effects in laboratory studies or the diseases in epidemiological studies that it appears to have caused. In other words, the seminal question is whether the toxic agent can cause the plaintiff’s disease, given the available information characterizing the effects the agent is capable of causing. If the evidence did not support an opinion that the toxic agent can cause the plaintiff’s type of disease, it would be logically impossible for an expert witness to conclude that it did so in the plaintiff’s case. The expert’s opinion whether the toxic agent can cause the disease complained of must be based on the strength of existing scientific studies; that is, on the basis of the studies’ number, quality, and degree of relevance to the toxic agent involved in the case.56
The legally significant question that arises concerning the can cause opinion is: Considered as a scientific statement, is it true?57 No witness can testify with complete freedom from possible error because sensory physiology and rational inference are fallible. These are the only two processes by which a witness can acquire knowledge cognizable at law. Thus, an expert who testifies on the basis of scientific studies cannot do so with absolute certainty.
Although the individual studies considered by the expert usually involve cause-and-effect relationships that are ninety-five percent,58 the expert necessarily incorporates subjective considerations in forming a can cause opinion.59 Thus, it is not possible for an expert to conclude with a numerical degree of certainty that a toxic agent can cause the plaintiff’s type of disease. As with all conclusions in science that are not themselves the direct result of scientific studies, the inductive inference must be stated using qualitative terms such as “possible,” “likely,” or “nearly certain.”
There is no explicit scientific convention regarding the exact meaning of the various terms routinely used to qualify the degree of truth of a generalization, but the definition of these terms can be discovered from an analysis of their use patterns. Not surprisingly, truth-qualifying terms are used in science as in other areas of human endeavor. “Possible” means only that the causal relationship is not impossible. In science, “possible” can be applied to any asserted causal relation because none are impossible.60 The term “reasonably possible” refers to causal statements whose probability of truth is greater than the naked minimum (anything greater than zero). “Probable” and “likely” indicate that the statement is more than fifty percent certain. The can cause opinion in a toxic tort case necessary to subject the defendant to liability is that, “it is probably true that X can cause Y,” because the burden is on the plaintiff to establish his case by a preponderance of the evidence.
Disease is a complex process involving many biological changes. Any cause-and-effect relationship between a toxic agent and a biological change is probative with regard to the fundamental issue of disease causation in human subjects. For example, if test-tube and animal studies show the toxic agent affected cell division, cell metabolism, the immune system, growth, healing, or reproduction, as reflected in the relevant laboratory variables, it might be reasonable to infer that the toxic agent probably can cause disease in human subjects because changes in one or more such variables invariably manifest when disease occurs. Similarly, if associations appear in epidemiological studies between exposure to the toxic agent and the plaintiff’s type of disease, then, depending on the number and quality of such studies, the proposition “it is probably true that X can cause Y” may be justified.
The question often arises as to how many test-tube, animal, and human studies are needed before an expert is justified in asserting that the causal relationship is “probably true.” This question can be resolved only by ascertaining how many such studies, and of what type and quality, ordinarily are required when the toxic agent or other similar agents are considered in relation to issues other than those involved in toxic tort lawsuits. Such issues include claims of medical efficacy of a drug, specification of the nature and severity of likely side effects of such drugs, and assertions of the absence of adverse health impacts due to a food additive or air pollutant.61
The alternative to a can cause conclusion is not a can’t cause conclusion. Rather, the conclusion is that the evidence does not warrant an inference of can cause according to the subjective level of certainty used in asserting a causal connection (“possible,” “likely,” and so forth).62 In other words, the two possible results of an individual experiment are either that the investigator found or did not find that “x” caused “y”. The alternative to “I found that x caused y,” therefore, is “I did not find that x caused y,” rather than “I found that x did not cause y,” because not finding “y” is not a possible observation.
B. Exposure to the Toxic Agent
Normally, the expert in a toxic tort case has no personal knowledge of the amount of the toxic agent received by the plaintiff because the expert neither measured nor observed it. In the radar gun example, the officer was exposed to different strengths of the radar field depending on the angle between the axis of the gun and the officer’s body, the reflection characteristics for electromagnetic fields of the patrol car’s glass and metal surfaces, the number of hours per day the officer operated the radar gun, and the years of exposure. The expert did not observe any of these factors during the time the plaintiff operated the radar gun. Nevertheless, the expert must demonstrate that he possesses the requisite knowledge regarding the plaintiff’s exposure to the toxic agent.
The expert must know the plaintiff’s dose of the toxic agent relative to the doses employed in relevant animal studies, and to the doses received by the subjects in relevant epidemiological studies. If, in the previous example, the amount of electromagnetic fields the officer received was similar to the amount received by a person who did not operate a radar gun, there would be no basis to assert that the cancer was caused by the fields produced by the radar gun, as opposed to the levels generally present in the environment. Thus, the expert must show that the plaintiff’s level of exposure to the toxic agent was greater than that ordinarily received by persons who do not develop the plaintiff’s type of disease.
An expert’s knowledge regarding the absolute and relative amount of a plaintiffs exposure to a toxic agent is based on the testimony of other witnesses and the results of tests and measurements made to mirror the plaintiff’s exposure to the toxic agent. On the basis of this knowledge, the expert must construct and render plausible a model of the plaintiff’s exposure that, to a legally acceptable level of certainty, permits the expert to estimate the dose the plaintiff actually received.63
C. Principal Deductive Opinion
If the expert sustains the burden of showing that “it is probably true that X can cause Y,” the question then arises whether the amount of toxic agent the plaintiff experienced probably caused his disease. Assume the plaintiff had no exposure to any other agent that also could cause his type of disease, and his exposure to the toxic agent occurred at significantly greater levels than those routinely experienced by persons who do not manifest the plaintiff’s type of disease. An expert could justifiably conclude that, although the possible causative role of unknown factors cannot be eliminated, the existence of only one potential cause sufficient under the circumstances makes it likely that it was the actual cause of the plaintiff’s disease. On the other hand, if the plaintiff had been exposed to additional agents shown by scientific studies to be sufficient causes of the plaintiff’s disease, a more complex factual issue exists. Accordingly, the relative importance of multiple agents in causing the plaintiff’s disease must be determined from an analysis of the quality and amount of pertinent scientific evidence.
When reasoning deductively in a toxic tort case, the concept of causality employed by the expert is identical to the but for conception employed by the layman in everyday life. The but for concept of causality is ordinarily the basis of liability in tort and is the core meaning of cause throughout the law.64 The expert’s testimony will be that the plaintiff’s disease probably would not have occurred when it occurred “but for” his exposure to the toxic agent. From an operational viewpoint, this testimony is equivalent to an assertion that erasing the history of the plaintiff’s exposure to the toxic agent, but making no other, changes in the circumstances involving the plaintiffs life, probably would have eliminated the occurrence of the plaintiffs disease at the time it actually occurred.
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VI. ADMISSIBILITY OF SCIENTIFIC EVIDENCE IN TOXIC TORT CASES
The court must evaluate the admissibility of the expert testimony before it may be considered by the trier of fact.65 The basic question a court must consider when determining the legal admissibility of scientific testimony is the reliability of the expert’s scientific knowledge. Since the court cannot decide the scientific issues,66 it must focus on the expert’s decision-making process, that is, the method by which the expert arrived at the opinion.
The court essentially must answer two questions: (1) Was the expert’s conclusion based on controlled observations of nature published in peer-reviewed scientific literature?; and (2) Were the applicable principles of scientific inference properly applied to the scientific data? If the court answers both questions affirmatively, it follows that it is “reasonably possible” the testimony is true, and therefore reliable. The court’s gatekeeping function, therefore, has been fulfilled. Any standard of truth greater than “reasonably possible” would usurp the function of the trier of fact.6767 Conversely, a lesser standard would amount to an abrogation of the court’s responsibility to assess reliability. The court’s function is to determine whether an inference may reasonably be drawn by a jury, or whether it must necessarily be drawn. The jury’s role is activated whenever the court finds the degree of certainty of the inference is between the two poles.
A. Modern American Jurisprudence Regarding Reliability of Expert Testimony: Frye to Daubert
Modern American jurisprudence regarding reliability of expert testimony began in a 1923 criminal case, Frye v. United States.68 This jurisprudence developed primarily in the criminal law, but ripened for definitive analysis in a toxic tort case, Daubert v. Merrell Dow Pharmaceuticals, Inc.,69 decided in 1993. In Daubert, the Supreme Court parsed the Federal Rules of Evidence and held reliability of scientific testimony must be determined by considering how the expert arrived at his opinion.70
Although Daubert has been significant in the development of the toxic tort cause of action, the implications of Daubert extend far beyond tort law to all cases in which scientific evidence is sought to be introduced. Before Daubert, courts had historically treated science as objective and dispassionate a source of knowledge but not a source of error.71 Based on this deferential view of science, courts found it unnecessary to ask the scientific expert, “How do you know?” In reality, however, science is no more objective and free of bias than are other areas of human endeavor. The courts’ absolute faith in scientists, therefore, was misplaced. Had it not been for the mid-course correction of Daubert, the law would have continued to evolve along a path that is hopelessly inconsistent with the nature of modern science.
The initial standard for determining the reliability of expert testimony was laid down in Frye, which otherwise was an ordinary murder case. James Frye, the defendant, passed a lie-detector test, and offered the polygrapher’s testimony regarding the results as evidence of his innocence.72 The defendant’s expert maintained that lying was always accompanied by a fear of being caught, and that this fear produced a rise in blood pressure that could be detected by a machine.73 The court held that “the thing from which the deduction is made74 must be sufficiently established to have gained general acceptance in the particular field to which it belongs.”75 The Court concluded that lie detectors “ha[d] not yet gained such standing and scientific recognition among physiological and psychological authorities as would justify the courts in admitting testimony deduced from the discovery, developments and experiments thus far made.”76 Although the “general acceptance” requirement was first applied against a criminal defendant in Frye, for the next half century, criminal defendants invoked the rule to prevent prosecutors from using new scientific developments to achieve unjust convictions.
While Frye was adopted in criminal cases in all the federal circuits and most state courts, it had no significant impact in civil cases.77 The advent of the toxic tort cause of action, however, provided a new area for application of Frye because each toxic tort case involved an assertion that an agent previously regarded as safe was not safe under some circumstances.78 Consequently, defendants found it advantageous to assert the “general acceptance” rule in toxic tort cases and thereby gain the benefit of the pre-existing presumption of safety. The effect of the rule when applied in toxic tort cases was to permit a party to shield its activities from substantive evaluation.79
The rule equating reliability with general acceptance was a form of judicial solipsism, because the only practical procedure for meeting the burden of Frye was to persuade the court to judicially notice the disputed principle. Consider, for example, a good faith attempt to meet the Frye burden. Initially, the identity of the persons whose “general acceptance” opinions the court will consider must be ascertained, but this is a difficult task because there are no credentialling agencies in science that designate such persons.80 A further difficulty arises concerning the reliability of each opinion in the authoritative group: What standard should the court apply? The standard obviously cannot be “general acceptance.” The means by which the group of opinion holders should be sampled to obtain their opinion raises an additional problem, because the conduct of valid surveys is itself a science.18 Therefore, the survey results would be inadmissible based on the Frye rule, unless their proponent first showed the principles followed in conducting the survey had gained “general acceptance.”
Another fundamental difficulty with applying Frye to toxic tort cases is that the rule tends to prevent establishment of precisely the factual conditions required to satisfy it. Testimony by the plaintiff’s expert that a toxic agent can cause disease will always be met by contrary testimony from the defendant’s expert.82 The defendant’s expert testimony is frequently based on scientific studies designed or controlled by the defendants. Thus, a rule that predicates the absence of reliability solely on the presence of controversy induces a defendant to create controversy, and thereby gain standing to invoke the rule.83
The United States Supreme Court, in Daubert, considered whether a plaintiff’s principal inductive opinion, in a toxic tort case or otherwise, need be generally accepted before it may be presented to the trier of fact.84 Daubert involved the morning-sickness drug Bendectin. The FDA approved Bendectin in 1956, and millions of pregnant women took the drug.85 Subsequently, concern arose that Bendectin might be capable of causing birth defects in the offspring of women who took it early in their pregnancy.86 Laboratory, animal, and epidemiological studies were performed to evaluate the issue.87 The FDA periodically revisited its original decision, but continued to permit the sale of Bendectin.88 Nevertheless, Merrell Dow, Bendectin’s manufacturer, eventually took Bendectin off the market in the face of several thousand lawsuits alleging that use of Bendectin had resulted in harm.89
In the trial court, the Daubert plaintiffs presented eight experts who concluded, on the basis of laboratory, animal, and epidemiological studies, that Bendectin can cause birth defects.90 Merrell Dow moved for summary judgment based on the affidavit of one expert who testified that the opinions of the plaintiff’s experts were not generally accepted.91 The court granted summary judgment in favor of Merrell Dow, citing Frye,92 and the Ninth Circuit affirmed on the same basis.93
The question presented to the Supreme Court was whether “general acceptance” was the appropriate standard for admitting scientific testimony that was contested for unreliability.94 The Court specifically rejected the Frye rule and held that “scientific … knowledge” was the applicable standard as provided in Rule 702 of the Federal Rules of Evidence.95 Daubert reaffirmed the proposition that the reliability of an expert opinion is a question of evidentiary law. If the opinion is “scientific … knowledge,” it is sufficiently reliable and can be admitted if it is relevant and not prejudicial.96 The standard for the degree of certainty that ultimately must be met is defined by the applicable substantive law.
The Daubert Court found the authority for a standard based on scientific knowledge in the Federal Rules of Evidence. Regardless of whether Congress or the drafters of the rules actually intended this result, the nature of modern science has rendered such a standard inevitable. Historically, juries regarded scientists with awe,97 but the judicial tendency toward such reverence has decreased in recent years. Perhaps this change reflects an evolving perception that scientists are not deserving of, and therefore should not be routinely accorded, an exalted status. Historical metaphors of the scientist as devoid of emotions, bias, error, and personal values are now commingled with other metaphors such as that of the partisan and the spin doctor.98
B. The Hearsay Rule
With the exception of scientific data actually obtained by the expert, scientific knowledge that forms the basis of an expert’s testimony regarding causality is hearsay.99 Nevertheless, the interests of justice sanction the use of one scientist’s data by another scientist. There are several cogent reasons, however, that the hearsay exception should prohibit the expert witness from relying on the opinion of another scientist or of a blue-ribbon committee,100 either in support of or in lieu of the expert’s own analysis.
First, the court has a nondelegable duty to assess the testimony of each expert whose opinion is offered as evidence in support of the truth of the matters contained therein. If the testifying expert is permitted to rely on the opinions of others, it is the expert, rather than the court, who effectively determines the admissibility of the testimony with regard to the qualifications and competency of the hearsay sources. Second, if experts testify on the basis of opinions held by others, opposing counsel is effectively precluded from cross-examining those who formulated the opinions. Important considerations, such as the potential bias or lack of credibility of the scientists or committee members, therefore, could not be pursued.
Third, with regard to a blue-ribbon committee report, the consensus language contained therein is frequently ambiguous. As a result, it may be merely the witness’s spin on the committee’s report that is actually placed into evidence. Fourth, blue-ribbon committees often confound the scientific issues regarding causality with policy considerations involving cost, fairness, allocation of the burden of proof, and subjective notions regarding the quantum of proof needed to prove the existence of a causal relation. The role of an expert witness in a toxic tort case involves only factual issues. All questions relating to policy and values should be reserved for the court. It would be an abrogation of the court’s role as the sole determiner of legislative intent to permit such decisions to be made by a blue-ribbon committee appointed by an executive authority, or by a private party.
Fifth, the possibility of bias should ordinarily exclude the use of hearsay sources of opinion. Individual scientists and blue-ribbon scientific committees ordinarily do not render spontaneous opinions regarding controversial scientific issues for purely altruistic and scientific purposes.101 Some bias-free information would be excluded by a rule that excludes reports of blue-ribbon committees, and such a rule would involve the court more deeply in adjudicating scientific matters than would otherwise have been the case. But when a choice must be made between relying on either a technically elite and knowledgeable group that is biased or potentially biased, and a scientifically unsophisticated but unbiased court, society is better served by the latter choice.
For these reasons, courts normally should not accept expert testimony based on the opinions of other experts. The scientific expert addressing causality in a toxic tort case should be restricted to testimony regarding his own opinions. The expert witness’ expertise lies in evaluating scientific data and rendering opinions thereon, not in conducting polls to apprise the court of the opinions of others, or in parroting the results of analyses performed by others. The individual reports on which an expert will rely should be established prior to trial, and a court order should be granted to limit or control the Use at trial of specific hearsay items, which are frequently well-known among those having all interest in particular toxic agents.102
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VII. EVALUATION OF SCIENTIFIC REASONING BY THE TRIER OF FACT
A. The Expert’s Choices of Method and Data
If the court is satisfied with the expert’s qualifications, and with the basis upon which the principal inductive and deductive opinions were formed, the expert will be permitted to opine to the trier of fact that “X can cause Y” and “x caused y.&lrdquo;103 The trier of fact then determines whether the expert’s opinions are probably true, after considering the method by which the expert reached his opinions. The proper basis for the expert’s opinion normally consists of nonpartisan scientific data published in the peer-reviewed scientific literature. On their face, these studies will purport to have established, or to have failed to establish, various cause-and-effect relationships involving the toxic agent under the particular circumstances of the studies. The plaintiff’s expert must rely on a group of such studies which he finds were performed at an acceptable level of competence. With respect to each study the plaintiff’s expert finds trustworthy and pertinent, he must make the basis for his view clear to the trier of fact. The plaintiff’s expert must explain why the studies are pertinent and trustworthy using layman’s terms.104 If the expert is unable to do so, the plaintiff cannot sustain his evidentiary burden.
The defendant’s expert, if attempting to persuade the trier of fact that a study contains errors which make it unreliable, is subject to the same rules that apply to the plaintiff’s expert.105 In particular, the defendant’s expert must produce the objective factors that guided his judgment, and it must appear that his judgment was a consequence of these objective factors. The questions regarding whether the expert has chosen, analyzed, and relied upon particular scientific studies on the basis of a scholarly and dispassionate analysis of all the pertinent literature, and whether the opinions based thereon are probably true, are fundamentally important in every toxic tort case. Determination of these issues is a difficult challenge to judges, lawyers, and the trier of fact because they often involve arcane scientific terms and concepts.
Many factors may affect the trier of fact’s determination of the credibility of a particular expert’s testimony. The trier of fact could decide that an expert’s opinion was improper if the expert accepted or rejected studies based on his a priori opinions rather than on the scientific merits. For example, in a hearing involving the safety of powerlines, an issue developed concerning whether electromagnetic fields produced by powerlines could cause biological effects in exposed animals.106 The opposing counsel challenged an expert for the power company on cross-examination with studies that reported biological effects in animals due to electromagnetic fields, and asked whether the expert had considered them in reaching his conclusion that no effects existed.107 The expert elaborated criteria for accepting scientific data, applied them to the positive studies, and concluded that those studies had no scientific value. The cross-examiner then asked whether the expert had similarly applied the criteria for acceptable scientific data to the negative studies.108 The expert stated he had not done so, and that he simply accepted the results of such studies because the results were as he believed they should be.109
The generation of expertise in contemplation of litigation may also signal to the trier of fact that a witness has failed to adhere to proper norms of scientific analysis. A witness who acquires his expertise regarding the causal potential, or lack thereof, of a particular toxin solely to take part in a specific legal dispute may have done so without thoroughly considering the pertinent scientific data. Examples include a physician who is not knowledgeable regarding the pharmacology of Bendectin or other similar drugs, or an electrical engineer with no knowledge of biology. If these experts are hired to give testimony and subsequently opine that Bendectin can cause birth defects or that electromagnetic fields can cause cancer, their testimony would be of dubious validity because their principal inductive opinions were based on knowledge acquired in contemplation of litigation. It is not reasonable to expect that such an instant expert would have developed the experienced judgment necessary to testify on such matters. The expert should possess knowledge that is pertinent to the case and acquired pursuant to a course of study and experimental inquiry, rather than for the purpose of litigation.
A related kind of dubious expertise consists in the proffering of testimony not actually authored by the testifying witness. This occurs when opinions for or against the view that “X can cause Y” reside in the word processor of a consulting company, which then hires scientists with an appropriate educational background and teaches them the canned analysis.110 The integrity of the law’s reliance on an expert requires that the witness actually possess substantive knowledge in the subject of the testimony and not merely be an actor playing a dramatic role in the courtroom. It is the responsibility of counsel to demonstrate such shortcomings on the part of opposing witnesses.
B. Principal Inductive Opinion
In a toxic tort case, the plaintiff’s experts, relying on a number of scientific studies in which the toxic agent was observed to produce various biological changes under different circumstances, will opine that it is probably true that the toxic agent can cause the particular disease involved in the case.111 The ethically preferable method of evaluating the likely effects of putative toxic agents on human beings is to observe the effects on animals and extrapolate the results to human beings.112 Indeed, an intention to reason in such a fashion is usually the justification for performing animal studies.
If animal studies showed that a disease similar to the plaintiff’s disease occurred in the test animals, the data would obviously be directly probative of the principal inductive opinion “X can cause Y.” Unfortunately, the animal version of a corresponding human disease is rarely a suitable observational endpoint because of time and cost considerations associated with animal studies.113 Consequently, although animal studies constitute the bulk of scientific research performed for the purpose of evaluating health risks, only a tiny portion of animal research is directly aimed at producing disease states in animals. Thus, scientific knowledge from animal studies is normally used indirectly to evaluate the correctness of the inductive inference.114
Frequently, the role of environmental factors in causing human disease is first discovered through epidemiological studies. The links between cigarette smoking and cancer, asbestos and cancer, and Agent Orange and certain skin diseases were all inferred from an analysis of disease patterns in exposed subjects. If an expert’s principal inductive opinion cannot be sustained on the basis of animal studies, it should be based on epidemiological studies. Further, if the peer-reviewed scientific literature contains both animal and human studies, the expert must demonstrate that both kinds of studies have been considered and that the inferences independently derived from each type of study are consistent. Any apparent conflict must be resolved before the expert’s overall conclusion can be accepted by the trier of fact.
The defendant’s expert carries a similar burden in situations in which there exist relevant data from both animal and epidemiological studies. In other words, if the defendant’s expert is to sustain an opinion that “X can cause Y” is untrue or unproven, he must do so based on all, not part, of the evidence. For example, in a trial involving the issue of whether electromagnetic fields from powerlines can cause cancer, the power company presented an expert who testified that the principal inductive opinion was untrue based on animal studies.115 A second expert reached a similar conclusion, based solely on an analysis of the epidemiological studies.116 In closing arguments, counsel for the power company asserted that since neither the animal nor the epidemiological studies supported the plaintiff’s principal inductive opinion, it was untrue or at least not proven to be true to an acceptable degree of certainty.117 It is improper, however, for an expert to opine regarding the truth of a proposition without considering all of the available relevant data. Even if the defendant’ s first expert could explain away the animal studies, his conclusion would be improper in the absence of a simultaneous consideration of the human studies because that data could cure or overcome the perceived shortcomings in the animal data. A similar point can be made regarding the testimony of the defendant’ s second expert. The conjunction of the experts’ testimony does not cure the defect inherent in each expert’s reasoning.
The expert’s reasoning regarding the truth or falsity of “X can cause Y” can be further assessed from the perspective of its implications. For example, consider a claim that Bendectin can cause birth defects. Animal studies have shown that Bendectin can cause various physiological changes. Based partially upon evidence of these changes, the drug was claimed to be beneficial for treatment of morning sickness and approved for sale by the FDA.118 The drug company’s experts applied scientific principles of reasoning to extrapolate animal data to human subjects and motivated the FDA to infer a benefit to humans.119 Thus, an expert may undercut his credibility if he argues that some animal studies cannot be interpreted or extrapolated to human subjects so as to indicate human risk, when he or his client have extrapolated animal studies to human subjects to rationalize a conclusion of human benefit. There is only one set of scientific rules governing the application of animal data to humans, and it is not dependent upon the result of the inference—whether it portends good or harm for human beings.
The trier of fact, particularly when properly assisted by counsel, can also evaluate the trustworthiness of an expert’s reasoning process by considering the expert’s nature and degree of advocacy. It is natural for an expert to display conviction, interest, and even passion regarding the various scientific studies he discusses, because the proper expert will be a person who has devoted a significant portion of professional time and effort to the subject of the testimony. In the process, the expert may, understandably, have developed subjective feelings regarding his testimony’s importance, but an expert who functions as an advocate, by emphasizing the evidence that supports his opinion and de-emphasizing data that suggests a contrary inference, fails in his basic responsibility—to teach the trier of fact the meaning of the applicable corpus of scientific knowledge.
For example, in a hearing regarding the safety of high-voltage powerlines, a power company expert testified regarding the implications of a scientific study, authored by Dr. Good, with regard to the possibility that electromagnetic fields can be hazardous. Dr. Good’s report described an effect on cells caused by electromagnetic fields, thereby suggesting that similarly exposed human subjects might also be affected. Initially, the expert believed the fields Dr. Good used were different from those produced by powerlines, and consequently concluded the study results had no implications regarding possible risks om powerline fields. The expert also testified that Dr. Good’s study was excellent. Following extensive cross-examination, however, the expert was forced to agree with the cross-examiner that the two fields were essentially comparable. This being the case, the cross-examiner suggested that Dr. Good’s study indicated that powerline fields were a human health risk. The expert then changed his previous testimony and said that Dr. Good’s study was inferior and of no scientific use.120
Unfortunately for the trier of fact, there are many shades and styles of scientific advocacy, and they are usually less obvious than that of the witness in the previous example. Furthermore, scientific advocacy may involve concepts that are pertinent to only one form of toxic agent and not to another.121 Consequently, a high degree of vigilance on the part of the opposing counsel is required with regard to each step in the expert’s chain of reasoning.
Attention to the structure of the expert’s chain of reasoning may reveal the tacit incorporation of assumptions that could sustain the expert’s opinion if true, but that are in fact false or unproven. One example is the implicit assumption that “X can cause Y” is true only if all or a majority of the pertinent animal and human studies were positive. For example, in a case in which the plaintiffs sought an injunction to overturn a school board requirement that their children must attend a neighborhood school that had been constructed next to a high-voltage powerline, the expert for the power company testified that some studies of the association between electromagnetic fields and cancer were positive and others negative. According to the expert, in the face of this conflicting evidence, it would be untrue to say that powerlines can cause cancer.122 The fallacy of such an argument lies in the assumption that all or most of the pertinent studies must be positive to warrant acceptance of a causal relationship. As discussed above, a negative study does not mean “X can’t cause Y,” but rather that the investigator found insufficient evidence to support the truth of the proposition that “X can cause Y.” If there is I positive study and 100 negative studies, and it is assumed that all 101 studies were done properly, the only correct inference would be that “X can cause Y.” An expert who evaluates scientific studies on the basis of relative numbers signals to the trier of fact either a result-oriented or policy-driven analysis.123
Another style of faulty reasoning is the invocation of the necessity to know the mechanistic causes of disease. The expert who can delineate the specific causal chain by which a particular toxic agent produces disease would be a powerful witness, and the testimony would undoubtedly merit acceptance by the trier of fact. But no such witness exists with regard to any toxic agent. No witness, for example, can authoritatively opine as to which of the several thousand agents present in cigarette smoke causes cancer, how such agents enter a cell, are transported or cause other substances to be transported into the cell nucleus, or how any such nuclear substances interact with the cell’ s genetic material thereby resulting in genetic aberrations that manifest as cancer. Absence of knowledge regarding cellular or molecular mechanisms that give rise to carcinogenesis is irrelevant to the consideration whether a cause-and-effect relationship between a toxic agent and a disease actually exists. Consequently, it is specious scientific reasoning to urge that mechanistic understanding is a condition precedent to acceptance of the principal inductive opinion.124
C. Principal Deductive Opinion
In a toxic tort case, the plaintiff must prove by a preponderance of the evidence that he was actually exposed at a particular level or range of the toxic agent. This may necessitate a witness with technical expertise in the method of measurement or characterization of the toxic agent. For example, if the plaintiff alleged that his disease was caused by an electromagnetic field produced by a high-voltage powerline located near his home, it would be necessary to show the existence and amount of the electromagnetic field created by the powerline at the plaintiff’s home, either by measurements or calculations. On the basis of lay testimony regarding the conditions of exposure to the toxic agent and expert testimony regarding pertinent characteristics and properties of the toxic agent, the expert must present a plausible model of the plaintiff’s activities from which the actual amount and duration of the plaintiff’s exposure to the toxic agent can be determined.
The expert must consider two distinct relationships involving the dose of the toxic agent the plaintiff received. The first involves the nexus between the levels of the toxic agent used in the pertinent scientific experiments and the dose the plaintiff actually received. Consider the case in which the scientific data linking the toxic agent and human disease were obtained using amounts of the agent that far exceeded the doses the plaintiff actually received. In such a case, the plaintiff’s expert faces a heavy burden in rationalizing the application of the scientific data to the plaintiff’s exposure because an agent that is harmful at high doses may not be harmful at low doses. Conversely, the defendant’s expert’s worst-case situation occurs when the dose of a toxic agent received by the plaintiff far exceeds the dose associated with adverse effects, as determined by the applicable human and animal studies.125
The second pertinent relationship the expert must consider is between the plaintiff’s dose of the toxic agent and the dose routinely received by members of the public from sources for which the defendant has no responsibility. Irrespective of whether the toxic agent can cause the plaintiff’s disease, it would be improper to hold the defendant liable for the plaintiff’s disease if the public, including the plaintiff, experiences comparable exposure to the same agent from sources not controlled by the defendant.126
In a toxic tort case, the plaintiff ultimately must establish that exposure to the toxic agent was sufficient in the circumstances to bring about the plaintiff’s disease. In other words, the plaintiff must establish that his disease would not have occurred when it did but for the dose of the agent he received. In this regard, the expert’s caused opinion is similar to his can cause opinion, and it is similarly subject to inquiry regarding the matters that affected its formation.
If the expert demonstrates from an analysis of the scientific literature and the evidence presented in the case that: (1) the plaintiff s disease can be caused by the toxin; (2) the doses of the toxic agent used in scientific studies involving the agent were comparable to the dose the plaintiff actually received; and (3) the plaintiff was exposed at levels substantially in excess of those experienced by ordinary members of the public, then the necessary conditions for scientific deductive reasoning have been met. In the simplest case, the plaintiff would have been exposed to only one risk factor, namely the toxic agent for which the defendant was responsible, and the plaintiff would have had no exposure to other known or suspected risk factors. In that situation, the expert’s principal deductive opinion—that the plaintiff’s exposure caused his disease—could be based squarely on the presence of one, and only one, known risk factor for the disease. The logically compelling force of the deduction would be derived from the elimination of all other known causes. Conversely, if multiple risk factors were present, serious questions of fact regarding the apportionment of cause might be raised.127
The expert’s reasoning that forms the principal deductive opinion is essentially identical to the reasoning process performed by experts more familiar at law, such as the expert who testifies in a medical malpractice case. A medical expert testifies that the plaintiff’s injury normally does not occur in the absence of a breach of due care. It is true of course, that the plaintiff’s injury could, in principle, result from many different causes, and it is theoretically possible that one or more of the other possible causes could have been operative in a given malpractice case, despite the absence of affirmative evidence thereof The medical expert can only indicate that a cause sufficient in the circumstances to result in the plaintiff’s injury was present, and that no other cause known to be sufficient in the circumstances was shown to be present. This fact pattern does not, of course, establish the truth of the medical expert’s opinion beyond a reasonable doubt. It does, however, establish the truth of the opinion to the degree of certainty deemed by the law to be sufficient for the imposition of civil liability. In the proper toxic tort case involving an expert’s testimony, both the procedure of the plaintiff’s expert in forming his principal deductive opinion, and the law’s rationale for accepting the form of the expert’s analysis used by the plaintiff’s expert, are essentially identical to the corresponding elements in the medical malpractice cause of action.
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