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4 Evidence Synthesis: The Question of Causation As noted earlier, one of the most difficult issues in toxic tort cases is causation. All three of the Supreme Court cases described above are centered on the evidence required to establish causation, an exercise that often involves synthesis of many types of data. The power of science arises from the objectivity of its methods. Scientists, nevertheless, generally recognize the limits of their methods and have developed best practices for addressing them: data sharing in open meetings, peer review, publication of results, disclosing conflicts of interests, and maintaining active research programs examining the validity of their methods as methods. Establishing general causation in science combines the analytic methods used in single studies with the synthetic methods used to summarize many studies (the bodies of evidence). No precise set of methodologic standards exists to establish causation in science, but that is what the courts seek: carefully drawn lines between evidence that establishes causation and that which does not. When parties to a case demand a decision, courts cannot wait for the experiments to be conducted, conferences to be held, or consen- sus to be built, and must therefore rely on available evidence at a given moment in time. In such a case, a plaintiff who cannot present relevant and reliable evidence on causation has not met his or her burden of proof, and under established law, should have his or her case dismissed. Some believe that the necessity faced by courts to decide cases before the science is fully developed raises questions about judicial management, that is, how and on what basis should 11

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DISCUSSIONS OF THE COMMITTEE ON DAUBERT STANDARDS judges make decisions about which experts to hear when relevant research is insufficient to point clearly toward causation. Scientific methods for determining cause differ from judicial methods (Hulka et al., 2000) and might even differ among scientific disciplines. Epidemiologic research offers an important example. Epidemiology studies obtain observational data on different groups of individuals to determine if exposure results in different outcomes. Methods used by epidemiologists to examine scientific evidence for general causation typically involve a system- atic narrative review of the literature that may exclude some studies on grounds of poor quality or lack of relevance. Within such a review, the so-called "criteria" of causation are applied to the summary body of evidence. The use of these criteria, which include an assessment of the current state of biological knowledge (some- times called "biological plausibility") has considerable flexibility built in so that scientists can select, prioritize, and assign eviden- tiary rules to these criteria with some impunity. What counts as a "weak association" for one user may be seen as a "consistent association" by another. In addition to biological plausibility, strength of association, and consistency of association, there are several other criteria in use, including "coherence," which is often considered to be an overarching summary consideration of the extent to which the evidence fits together as a whole. This method of determining general causation, which epidemiologists have been discussing at their open meetings and in peer reviewed literature, is as subjective as it is objective, and is more qualitative than quantita- tive (Weed, 2003). Each profession has its own standards for evidence. In the field of law it is sometimes difficult to square the legal standards of proof with the scientific standards of proof. Thus, courts must assess the range of acceptable disagreements within the scientific community and measure these various opinions against legal standards of admissibility and sufficiency of evidence. This sometimes can result in admission of questionable science or the 12

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Evidence Synthesis: The Question of Causation exclusion of what most would consider reliable science, or at the very least, inferential judgments such as clinical medical assess- ments in the absence of other evidence. Even though trial judges are expected to examine the underlying basis of testimony to ensure that only testimony sup- ported by valid methods of inquiry is admitted, judges are not always issuing consistent legal decisions in otherwise similar medical cases (Kassirer and Cecil, 2002). In some cases judges have excluded medical testimony on cause-and-effect relationships because it was not based on published, peer-reviewed, sound studies, even though in certain kinds of cases practitioners may rely on other evidence of causality in making clinical decisions when such data are not available. In effect, some courts have required standards for expert testimony that exceed those that relevant experts would use to assess causation. Finally, it has been the practice of some courts to assess evidence offered to prove causality piece by piece, that is, looking at the results of one scientific investigation as an isolated event rather than considering these findings in the context of other research. This is not the approach scientists would follow. Science accumulates knowledge incrementally. Before trying to answer a scientific question, a good scientist will look at what others have done to see if the answer might already exist, build on partial knowledge already discovered, and learn from the mistakes and insufficiencies of prior work. Thus, scientists consider it illogical to ignore a study simply because it did not offer a definitive answer to the question being asked. The tendency in science is to include rather than exclude such data for consideration. The committee discussed several areas where it might be useful to explore further the different approaches used by scien- tists, lawyers, and judges in the selection, summarization, and interpretation of scientific evidence when trying to determine causation. In particular: 13

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DISCUSSIONS OF THE COMMITTEE ON DAUBERT STANDARDS Are there distinctions between the way Daubert is functioning in the courts and the way scientists think it should function with respect to synthesis of evidence? Do courts and scientists agree on a hierarchy in types of evidence they select to consider, for example, in favoring evidence that comes from a particular discipline like epidemiology over another like toxicology? Do courts and scientists agree on how to assess indi- vidual studies? If a particular study is insufficient by itself to conclusively demonstrate causation is it there- fore unreliable evidence on which experts should not rely in drawing causal inferences? What are the scientific approaches to synthesizing a body of knowledge that includes different disciplines (e.g., toxicology, epidemiology, clinical research) or different methodologies within disciplines? To what extent is evidence synthesis in science a well- established (vs. a dynamic even controversial) practice? What guidelines exist to conduct evidentiary assess- ments in science? What kind of research/education needs to be done in this area? What advice can be offered to judges to use when considering a body of scientific information that in- cludes different study designs, methodologies, and disciplines? Another topic discussed was the availability of data from studies needed to establish causation. Some argue that there are cases where data should have been developed or made available, but were not. Concern about the availability of research results has been expressed by the biomedical community and recently the International Committee of Medical Journal Editors (ICMJE) published a joint editorial aimed at promoting registration of all 14

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Evidence Synthesis: The Question of Causation clinical trials (De Angelis et al., 2004). ICMJE stated that it will consider a trial for publication only if it has been registered before the enrollment of the first patient and took as its goal "to foster a comprehensive, publicly available database of clinical trials." Further, ICMJE called for such information to be publicly available "to guide decisions about patient care," as patients "deserve to know that decisions about their care rest on all of the evidence, not just the trials that authors decided to report and that journal editors decided to publish." Concerns about the availability of relevant studies, led several members of the NRC committee to ask if there should be consequences when an information gap exists because a party to a lawsuit failed to undertake studies that need to be done or failed to divulge negative results? 15

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