The End of the Era of Proxies

16 Pages Posted: 7 Mar 2011

See all articles by Edward J. Imwinkelried

Edward J. Imwinkelried

University of California, Davis - School of Law

Date Written: March 4, 2011


In the past, in deciding whether to admit testimony about a particular scientific technique or theory, American courts have largely relied on proxies for the validity of the theory or technique. Rather than directly evaluating the empirical data relevant to the validity question, the courts have turned to surrogates for validity. For example, they have employed such proxies as general acceptance by laypersons in the marketplace, general acceptance by experts in the relevant specialty field, and approval by governmental administrative agencies. To justify such reliance, the American appellate courts have often asserted that trial judges are incompetent to resolve genuine “battles of the experts” and that untrained lay jurors are inclined to overestimate the trustworthiness of expert testimony.

This reliance on proxies has been sharply criticized. To begin with, numerous psychological studies have called into question the assertion that lay juries are naively overawed by expert testimony. More importantly, the use of proxies has led to false negatives as well as false positives. Even if a theory lacks the requisite popularity or approval, the available empirical data may demonstrate its validity. Conversely, even when a theory enjoys the required popularity or approval, the data may establish its invalidity. Thus, there is significant tension between the use of proxies and the priority on rectitude of decision under the truth theory of adjudication.

In 1993 in Daubert v. Merrell Dow Pharmaceuticals, Inc., the United States Supreme Court ruled that federal judges may no longer use the proxy of general acceptance by specialists as the test for determining the admissibility of scientific testimony. At the same time, the Court mandated that lower federal courts employ an essentially epistemological approach to determining whether the proffered testimony qualifies as admissible “scientific . . . knowledge” under Federal Rule of Evidence 702. The majority of states have adopted some variation of this test.

The Daubert decision is challenging. The courts are writing on a tabula raza because, during the era of proxies, the courts accumulated little experience dealing directly with the empirical data relating to the validity of scientific theories. Daubert now mandates that judges do so.

American law has taken several steps to ensure that judges, jurors, and attorneys are up to the challenge assigned them by Daubert. To begin with, many American jurisdictions have greatly expanded the breadth of the pretrial discovery of expert information. This expansion gives the litigant a fair opportunity to critically evaluate the scientific reasoning of the opponent’s expert witness. In addition, there has been a proliferation of texts, courses, and continuing education programs designed to familiarize law students, lawyers, and judges with the rudiments of scientific methodology. Further, there has been an increase in the use of court-appointed experts and special masters in cases involving extensive scientific testimony.

There is no guarantee that even with the benefit of these measures, the American legal system will meet the challenges posed by the abandonment of proxies. However, there is good reason to be hopeful. In the past, particular segments of American legal practice such as the patent bar have demonstrated their ability to work with sophisticated expert information. In those areas, the bench and bar have proven themselves to be educable. In addition, as Sir Karl Popper famously observed, in the final analysis the scientific method is simply “common sense writ large.”

This topic is significant for three reasons. First, American litigants offer expert testimony in the vast majority of cases that go to trial. The courts’ ability to properly assess the expert testimony can determine the quality of the justice dispensed by the courts. Second, if the doubts about layperson’s ability to critically assess evidence have been overstated, it may be time to reconsider some of the other exclusionary rules such as the hearsay doctrine. Finally, the topic has broader implications for the issue of the courts’ institutional competence.

Suggested Citation

Imwinkelried, Edward J., The End of the Era of Proxies (March 4, 2011). UC Davis Legal Studies Research Paper No. 250. Available at SSRN:

Edward J. Imwinkelried (Contact Author)

University of California, Davis - School of Law ( email )

Martin Luther King, Jr. Hall
Davis, CA CA 95616-5201
United States

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