related tests: (1) the statutory wording that governs the level of scientific or engineering certainty about toxicity or product risk; (2) the specific level of protectiveness required (e.g., “ample margin of safety” or the absence of “unreasonable risk”); and (3) whether the findings are governed by a legal test of deference to an agency decision (“preponderance of the evidence” vs. “arbitrary and capricious”).1

The courts apply no single level of rigor for the science or other expertise used as evidence in civil litigation. The rigor applied by the court may vary as a function of the jurisdiction of the court (federal, state, adminis-trative law judge whether the case is governed by common law or statute) and of the stakes involved. Higher stakes (e.g., major injuries, massive recalls) sometimes appear to require more evidence and a higher level of proof of causation. In addition, juries may be more skeptical of evidence if a verdict will result in an enormous award or threaten the viability of a major institution. The rigor of scientific evidence may vary with the purpose of the inquiry; a lower level of rigor may be required to simply list a substance as “toxic” for reporting purposes (e.g., for the Toxic Release Inventory), a higher level to impose regulatory restrictions, an even higher level to award huge damages, and a higher level still to ban a substance from use.2

One arena that has proven especially troublesome for courts is the question of causation in so-called toxic tort cases, which might be considered as a subspecies of product liability litigation.3 Because many of these cases turn on points of technical complexity, expert witnesses are often required to provide testimony. Much is at stake—the viability of firms or whole industries, the ability for injured parties to receive ade-quate compensation, and costly litigation burdens and settlement sums. Therefore, courts have tried hard to improve their standards for admitting and weighing scientific and technical evidence.


See, e.g., Chevron U.S.A., Inc. v. Natural Resources Defense Council, Inc., 467 U.S. 837 (1984), Christensen v. Harris County, 529 U.S. 576 (2000) . See also Ernest Gellhorn & Paul Verkuil, Controlling Chevron-Based Delegations, 20 Cardozo L. Rev. 989 (1999), U.S. v. Mead Corp., 533 U.S. (2001).


There are also important distinctions among rigor (the reliability of evidence), accuracy (test variability), and precision (the level of accuracy to which a test can measure).


The prevalence of toxic tort litigation, which seeks to resolve claims by individuals that they have been injured by exposure to chemicals or other products, has grown rapidly in recent years, amid considerable controversy. Some people criticize toxic tort litigants for seeking to impose liability for exposures that carry little or no risk to individuals (e.g., air pollution), especially when compared to other, larger risks under a person’s voluntary control (e.g., driving, smoking). The law reflects this distinction, however, and finds relatively low risks that are involuntary to be actionable or sufficient to warrant regulation.

The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement