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From: A.A. Marino & L.E. Marino: The Scientific Basis of Causality in Toxic Tort Cases, Dayton Law Review, vol. 21, pp. 1-62, 1995.
The requisite evidence in a toxic tort case consists of scientific knowledge, which is the collective result of individual scientific experiments as memorialized in peer-reviewed scientific journals and other appropriate written repositories, and appropriate inductive generalizations and deductive inferences based thereon. In contrast to what is true of individual scientific studies, the degree of certainty of an inductive inference cannot be stated in mathematical terms because it is a judgment. Thus, the inference that "cigarette smoking causes cancer" cannot be stated with numerical precision, although the results of particular experiments involving animals or human subjects exposed to cigarette smoke under particular conditions can and must be quantified to constitute part of the corpus of scientific knowledge.
The expert's testimony is based on scientific knowledge, and therefore he must possess training and experience sufficient to enable him to analyze and explain the laboratory and epidemiological studies pertinent to the effects of the toxic agent on cells, animals, and human beings. The training ordinarily expected of such an expert includes a Doctor of Philosophy degree in science, because it is evidence that the witness received the highest level of formal training in scientific methodology and reasoning. Performance of experiments involving the toxic agent and subsequent publication of the results in the scientific literature is the best evidence of scientific expertise. If the witness earned a Ph.D. in science and performed many experiments and published many scientific articles involving 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.
The amount of the toxic agent present in particular scientific studies in relation to the amount actually received by plaintiff is always a fundamental issue regarding whether the toxic agent caused plaintiff's disease. Thus, the expert's training and experience must also include knowledge of the laws or principles that govern the dosimetry of the toxic agent.
Unlike the physician or the technical expert, who are permitted to testify on the basis of professional status and anecdotal evidence, the expert in toxic torts must testify on the basis of scientific knowledge; consequently there cannot be a scientific expert in the absence of scientific knowledge. The customary process for validating scientific knowledge is peer review, whereby anonymous peers of a scientist judge the merits of scientific experiments or studies, the results of which are offered for publication. Peer review neither warrants that the results are good science nor suggests by its absence that they are bad science. Peer review is not a litmus test for truth, validity, or general acceptance, but it is the standard assessment procedure that precedes the addition of a particular study to the corpus of scientific knowledge. The expert in a toxic tort case should ordinarily rely on peer-reviewed reports to perform analyses and reach conclusions.
At most, peer review is an indication of the acceptability of a scientific report with regard to its intrinsic validity - that is, the validity of the report as determined from an analysis confined to the four corners of the publication. A further question regarding the extrinsic validity of a scientific study arises when a study relied upon was designed, conducted, or otherwise influenced by one of the parties in the litigation, or by someone in privity with these parties. An expert witness who chooses to rely upon particular scientific reports, therefore, has a responsibility to make a reasonable effort to establish their extrinsic validity, and the court, opposing counsel, and the jury should also consider the extrinsic validity of the reports relied upon by the expert when determining whether the expert's testimony is admissible, or how it should be weighed.
Blue-ribbon committees should enjoy no presumption regarding the qualifications or validity of the work product because both the membership and work product of such committees are invariably shaped by the appointing authority. The committee's decisions represent a consensus of the persons recognized as experts by the appointing authority, but those decisions bear no necessary relation to a consensus of all qualified experts. Consequently, the reports of blue-ribbon committees should not be admissible as evidence of the truth of the propositions that they recite.
The kinds of scientific studies potentially available for consideration by the expert in toxic tort cases regarding the question of causality are test-tube, animal, and epidemiological studies, and each has particular strengths and weaknesses. Although the limitations of animal or test-tube studies with regard to inferring causal relationships in human subjects must always be considered by the expert, it is unquestionably correct to use such data to form causal inferences, under the proper circumstances. The scientifically and ethically preferable data is that obtained from animal studies.
The expert in a toxic tort case must rationalize an assertion that the dosage of the toxin received by plaintiff and plaintiff's disease were causally related, and not merely associated with each other. The expert cannot rely on personal observation as the basis of a cause-and-effect relationship because the onset of human disease in a particular person is simply not amenable to direct observation in relation to a specific cause. Since an expert cannot rationalize a cause-and-effect relationship based on direct observation, the causal conclusion must be derived from scientific evidence, namely, an appropriate and reliable corpus of scientific data that permits the expert to infer what happened within plaintiff's body as a consequence of exposure to the toxic agent.
The logic of scientific reasoning constrains the order in which the expert must approach a decision whether plaintiff's exposure to the toxic agent and his subsequent disease were causally related or merely associated. The expert must first consider the pertinent scientific studies, and determine therefrom whether the toxic agent caused the effects reported in the laboratory studies and the diseases described in the epidemiological studies that it colorably appears to have caused in the individual studies. Thus, the seminal question is whether the toxic agent can cause the disease complained of by plaintiff, given the available information that characterizes the effects that the agent is capable of causing. The opinion must be based on the strength of the scientific studies; that is, on the number, quality, and degree of relevance of the studies to the toxic agent involved in the case. No causal assertion in science is certain, and only some causal assertions (the results of particular experiments) can be expressed to a numerical degree of certainty with numerical precision. The can cause conclusion of the expert is not the result of a particular experiment, and therefore must be stated using qualitative terms such as "possible", "likely", or "nearly certain." The expert's testimony must be sufficient to prove that "it is probably true that X can cause Y."
If the expert sustains the burden of showing that X can cause Y, the question then arises whether the amount of toxic agent experienced by plaintiff in the circumstances probably caused his disease. If the quantum of plaintiff's exposure to the toxic agent was not greater than that ordinarily received by people who do not develop plaintiff's disease, it would be unreasonable to assign a causal role to the toxic agent. Therefore, the expert must show that plaintiff was exposed to the level of a toxic agent greater than that ordinarily received by persons who do not develop plaintiff's type of disease. The basis of an expert's knowledge regarding the absolute and relative amounts of plaintiff's exposure to the toxic agent consists of the testimony of other witnesses, and the results of tests and measurements made in circumstances that are pertinent to those under which plaintiff was exposed. Assuming that plaintiff had no exposure to any other agent that can also cause plaintiff's type of disease, and that plaintiff's exposure to the toxic agent occurred at high levels of the toxic agent, then an expert could justifiably conclude that, although the possible causative role of unknown factors cannot be eliminated, the existence of only one known sufficient cause makes it likely that the single known risk factor present was the actual cause of plaintiff's disease.
The court has a gatekeeper role regarding the admission of scientific evidence. Before the expert's conclusions may be presented to the trier of fact, the court must be satisfied that it is reasonably possible that the conclusions are true. In making its determination, the court's focus must be on the expert's decisional process, that is, on how the expert arrived at the opinion. Was the conclusion based on controlled observations of nature published in the peer-reviewed scientific literature? Were the applicable principles of scientific inference properly applied to the scientific data? If both questions are answered in the affirmative by the court, it follows that it is reasonably possible that the testimony is true, and therefore reliable.
The scientific studies and reports that form the basis of the expert's opinion are exceptions to the hearsay rule insofar as they relate to scientific data, but not insofar as they relate to opinion. The scientific expert may not invoke the opinion of another scientist or a blue-ribbon committee, either in support of or in lieu of the expert's own analysis, because representations of opinions are not acceptable as a substantial part of the basis for an expert to testify for or against the truth of the proposition that "X can cause Y."
An expert in toxic tort cases carries a heavy burden because,
in the face of cross-examination and direct testimony by opposing witnesses,
he must choose valid scientific data on which to rely, and form his principal
inductive and deductive opinions thereon in a lucid and credible manner
so as to be understood and believed by the lay trier of fact. It is unlikely
that the trier of fact will be swayed by an expert who testifies in a manner
that is inconsistent with the scientific facts when the adverse party is
represented by able counsel.
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