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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
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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
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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:
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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
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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?
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Representative terms from entire chapter:
legal standards
