BRIEF AMICI CURIAE OF
The American Association For The Advancement Of Science (AAAS) And
The National Academy Of Sciences (NAS)
In Support Of Respondent

SUMMARY OF ARGUMENT

The courts below correctly recognized the difficulties that attend the consideration and use of scientific evidence in the courtroom. Such evidence often may be difficult to assess and yet may be of determinative significance. To avoid outcomes that are at odds with reality, courts must exercise special care to assure that such evidence is based on valid and reliable scientific methodologies.

Courts can best accomplish this difficult task by applying the same criteria that scientists themselves regularly apply in picking and choosing the theories, explanations, and methods upon which they build their own work. Although the details of science may be remote from common experience, judges can understand the fundamental characteristics that separate good science from bad. Courts should also consider the institutional mechanisms, namely the different forms of peer review, that have been developed to assure that scientists conduct their work in accordance with appropriate scientific criteria.

When faced with disputes about expert scientific testimony, judges should make full use of the scientific community's criteria and quality-control mechanisms. To be admissible, scientific evidence should conform to scientific standards and should be based on methods that are generally accepted by the scientific community as valid and reliable. Threshold determinations concerning the admissibility of to ensure accurate decisions and to avoid unnecessary expenditures of judicial resources on collateral issues. Judicial control of this sort is fully in keeping with the Federal Rules of Evidence.

ARGUMENT

SCIENTIFIC EXPERT TESTIMONY POSES SPECIAL CHALLENGES FOR COURTS AND NON-SCIENTIST FACT-FINDERS.

Scientific evidence can present special problems in litigation. It is often couched in peculiar terms, may derive from complicated scientific principles and seemingly unusual methods of proof, and sometimes addresses issues of fact that are very different from those confronted in everyday life. Because fact-finders may perceive expert scientific evidence as carrying a special stamp of certainty and authority, they sometimes give particular credence to scientific experts.

Scientific evidence may also have particular importance certain types of litigation because it can illuminate crucial issues that otherwise would remain in darkness. For example, in a toxic tort case, science can provide unique insights into the likelihood that exposure to a certain chemical caused the injury at issue. Such testimony may provide the sole foundation for determining whether a plaintiff can satisfy a causation requirement.

Finally, scientific evidence presents unique challenges because it may not be able to provide definitive pronouncements. Scientist must often be satisfied with probabilistic statements made m the context of particular theoretical assumptions or experimental methodologies. The proper consideration of scientific evidence requires sensitivity to those assumptions and methodologies and to the reality that scientific knowledge is often evolving and changing.

The unique persuasive power of scientific evidence -and its inherent limitations - requires that courts engage in special efforts to ensure that scientific evidence is valid and reliable before it is admitted. In performing that task, courts can look to the same criteria that scientists themselves use to evaluate scientific claims.

SCIENTISTS USE ESTABLISHED CRITERIA AND INSTITUTIONAL MECHANISMS TO EVALUATE SCIENTIFIC CLAIMS.

The scientific community has a special interest in encouraging innovative thinking while simultaneously ensuring that new ideas are subjected to rigorous review. On the one hand, science is a creative process in which advances occur only if researchers develop and test innovative ideas. Indeed, the scientific community reserves its highest honors for those individuals who have taken chances on novel approaches to problems. On the other hand, because science is a cumulative subject in which each scientist must build on the work of others, the, scientific community also places great emphasis on weeding out false ideas. Accordingly, creativity is tempered by the need for rigorous testing and review of new approaches.

Individual scientist must be able to identify "good" science in pursuing their own research. The fundamental criteria they apply in doing so are neither arcane nor remote, and can be understood by educated and informed lay persons. Similarly, judges can understand and rely on the institutional processes that science has developed to help evaluate scientific assertions.

Science Represents An Ongoing Process Of Inquiry To Explain Natural Phenomena.

Science is not an encyclopedic body of knowledge about the universe. Instead, it represents a process for proposing and refining theoretical explanations about the world that are subject to further testing and refinement. Scientists accept a scientific explanation for an event when that explanation is corroborated by experiments using accepted methodologies and when it is consistent with other accepted expirations. Corroboration is generally based on the correct prediction of observed events or results. In some fields, such as cosmology, consistency with general theory may be especially important. In other fields, such as biochemistry, experimentation provides the primary means for evaluating hypotheses. In still other fields, such as astronomy, observation rather than experimentation is relied upon to corroborate theoretical predictions. At its core, however, science is a process of evaluating testable propositions to assure conformance with observable reality.

In Pursuing Their Own Research, Scientists Routinely Evaluate The Work Of Colleagues.

In light of the immensity of contemporary scientific knowledge, no scientist could conceivably corroborate the validity of all of the theories, methods, and results on which he or she must rely in research. As a result, each scientist must decide whether to accept particular hypotheses or rsearch data as the foundation for further work. This process involves the weighing of a variety of factors to ensure that the underlying work is reliable.

Scientists evaluate whether an hypothesis has been rigorously tested and whether the data have been derived using methods or protocols deemed acceptable in the field. In conducting such an evaluation, scientists consider the credentials of the proponent of a particular hypothesis or of the source of the data, including whether the research is in a field in which the proponent's education or experience indicates expertise. Reliance on an hypothesis generated by another might also depend on whether the experimental evidence is sufficient to reject reasonable alternative hypotheses and is consistent with existing scientific theories pertaining to that field. Similarly, reliance on another's h data might turn on an evaluation of the consistency of the results with data gathered by several others in the relevant field.

These considerations do not, of course, exhaust the range of criteria that scientists use in evaluating scientific work, but they do reflect the basic concern for probing the foundations of research results to assess conformance with scientific standards. Scientist would, for instance, typically not be inclined to rely on an hypothesis based on nothing more than reinterpretations of existing data if the new hypothesis is uniformly inconsistent with the results of other previously published research. Because experimentation is itself subject to error, scientists also require replication of tests, particularly before rejecting important or previously corroborated hypotheses.

There is an obvious danger that research results generated solely for litigation may be skewed. "A scientist who has a formed opinion as to the answer he is going to find before he even begins his research may be less objective than he needs to be in order to produce reliable scientific results. Indeed, experts who testify about research results that have not been submitted for scientific scrutiny, despite ample opportunity for publication, may not be truly acting in their capacity as scientists. One court has observed that "many such able persons present studies and express opinions that they might not be willing to express in an article submitted to a refereed journal of their discipline or in other contexts subject to peer review."

Of course, not every scientific conclusion is of an importance that warrants publication or even detailed peer scrutiny. Some matters may have a significance in litigation that far exceeds their scientific interest. For example, the hydrological evaluation of a chemical waste site might have enormous import in litigation, but, unless some previously undetected phenomena were encountered, it would likely be of little general scientific interest. The test applied by scientists in evaluating such results would turn on whether their proponent has consistently adhered to the kind of reasoning that constitutes science, and has made plausible assumptions and used an accepted methodology in reaching his or her conclusions.

On the other hand, research results that are advanced solely in litigation and that conflict with existing learning should be viewed with caution. Such information, if correct, is of scientific significance and ordinarily would warrant publication. Experts who propose to do nothing more with seemingly remarkable discoveries than submit them to judges and juries are not acting in a manner characteristic of scientists. Presentation of the information to the scientific community in some fashion is the sole means by scientific knowledge.

C. Institutional Checks Exist To Assist In Evaluating The Validity Of Scientific Research.

A new theory or explanation must generally survive a period of testing, review, and refinement before achieving scientific acceptance. This process does not merely reflect the scientific method; it is the scientific method. Peer review, in its broadest sense, represents the scientific community's effort to police itself and to assure a certain minimum level of quality so that scientists and others can rely on the results of reported scientific research. Moreover, peer review contributes to the advancement of science not merely through the screening of scientific work, but also by helping proponents of new hypotheses to improve their research and interpretations.

This scientific scrutiny takes place in a variety of contexts. As one court has explained:

Scientific truth and the acceptability of scientific procedure are not normally established by public opinion polls. The scientific Community uses entirely different methods for such purposes (e.g., articles in learned journals, seminars, acceptance at institutions of higher learning). . . [These procedures] are time-honored precisely because scientific truth generally requires this kind of maturation of a consensus.

Informal peer review can occur when scientists discuss their work with one another at the laboratory bench, during conversations and seminars, and at scientific--meetings. Formal peer review is generally an intrinsic part of the scientific publication process and the process by which funds are allocated for the conduct of research. At a minimum, any claim that would significantly add to or change the body of scientific knowledge is regarded skeptically until it has been subject to some form of peer scrutiny.

COURTS SHOULD EXCLUDE EXPERT TESTIMONY DERIVED FROM THEORIES, REASONING, OR METHODOLOGIES THAT DO NOT CONFORM TO SCIENTIFIC CRITERIA AND STANDARDS.

Courts should admit scientific evidence only if it reasonably conforms to scientific standards and is derived from methods that are generally accepted as valid and reliable. Such a test for admissibility would incorporate the factors, including the results of peer review, that scientist consider in evaluating each other's work.

A. In Evaluating Disputed Scientific Evidence Courts Should Consider The Same Factors That Scientists Consider.

Although many judges may lack extensive scientific training, they can understand the basic characteristics that separate valid science from mere speculation. The scientific commitment to providing explanations that are supported by observational and experimental evidence should apply when an expert testifies in court, just as it does when he or she reports results to other scientists. Only in this way can prejudicial speculation be distinguished from valid science. Indeed, the basic logic of science does not differ from the logic of the law. In both, understandable explanations must connect evidence to conclusions about the evidence.

Courts can and should decide disputes about scientific evidence based on an understanding of the overarching principles that govern the way good science is conducted. For example, a physician should not be allowed to claim that a substance caused someone to develop a common illness simply because another of his patients developed a similar illness after years of exposure to the same substance. Similarly, an expert should not be permitted to assert that a substance is a human carcinogen on the basis of nothing more than inconclusive animal testing. Although these observations may provide an interesting foundation from which to generate h about causation that warrant careful exploration, no scientist would acres the offered conclusions, without more, as scientifically valid. Courts likewise should have no trouble in recognizing the shortcomings of such evidence if they assess these assertions against the basic criteria of scientific validity.

The characteristics of valid science are neither remote nor arcane, and a judge should not hesitate to consider them in evaluating disputed scientific evidence. Although judges often will be unable to bring the same expertise to such a task as a specially trained scientist, they are in a position to determine if scientific evidence possesses the characteristics of valid science and to consider the same factors that busy scientists use to evaluate research performed by other scientists. To the extent that a judge feels a need for additional information or guidance in making determinations of scientific validity, Rule 706 of the Federal Rules of Evidence authorizes the appointment by the court of experts to assist in such matters.

The community's well established and institutional mechanisms for evaluating the validity of scientific assertions provide courts with clear and understandable guidance on how they can rationally and consistently evaluate scientific evidence. Courts should admit scientific evidence only if it conforms to scientific standards and is derived from methods that are generally accepted by the scientific community as valid and reliable. Such a test promotes sound judicial decision making by providing workable means for screening and assessing the quality of scientific expert testimony in advance of trial.