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The Evolving Standards of Admissibility of Scientific Evidence

By Joseph T. Walsh

The emergence of genetic science poses significant challenges at both the substantive and procedural levels of litigation.

The use of scientific proof in a forensic setting has proven problematic for both judges and attorneys because most of them are not technically trained. Much of the difficulty encountered by courts when facing scientific evidence lies not in a lack of understanding the underlying science but in the task of choosing between competing scientific explanations tendered by individuals who seek to wear the mantle of experts.

Judicial discomfort in handling scientific evidence has increased in recent years with the emergence of scientific testimony offered by experts whose availability and malleability have earned them the sobriquet of "hired guns." Just as the controversy over roving "experts" was at its height, the role of judges in determining the admissibility of scientific and technical evidence was made more difficult by the 1993 U.S. Supreme Court’s decision in Daubert v. Merrell Dow Pharmaceutical, Inc., which abolished the seventy-year-old test for evaluating scientific evidence first pronounced in Frye v. United States. Under Frye’s simplistic teaching, trial courts, when faced with a challenge to the admissibility of expert testimony, determined whether the expert’s methods were generally accepted in the relevant scientific community. If so, the evidence was admitted with any deficiencies attributable to either the frailty of the underlying science or the expert’s qualifications, both matters of weight for the jury.

The underlying evidentiary issue in Daubert was the scientific validity of the methodology of studies offered by the plaintiffs to prove that a drug used by pregnant mothers to control nausea could cause birth defects. In considering that matter, the Supreme Court unanimously ruled that Frye did not survive the enactment of Federal Rule of Evidence 702, and some other approach was necessary. A majority of the Court then ruled that when confronted with novel or scientific evidence, the trial judge must assume the role of "gatekeeper" to ensure that the "expert’s testimony both rests on a reliable foundation and is relevant to the task at hand." In discharging the reliability task, the trial judge may use a variety of sources, including the testimony of experts. However, ultimately it is the trial judge’s decision whether the evidence passes the test of reliability.

Although the language of the majority opinion in Daubert appears to confer broad discretion on trial judges, it emphasizes the need to determine the reliability of scientific knowledge through its origin in the scientific method. To that end, the Supreme Court directed trial judges to consider at least four factors when determining admissibility: (1) whether the theory or technique can be tested, (2) whether the proffered work has been subjected to peer review, (3) whether the rate of error is acceptable, and (4) whether the method at issue enjoys widespread acceptance.


Whither Daubert? The Supreme Court’s ruling in Daubert is binding only on federal courts. One clear byproduct of Daubert is that trial judges, in discharging their gatekeeper role, are conducting more in limine hearings to assess the genuineness of scientific claims despite the risk that admissibility may turn on a highly subjective determination by a trial judge who may not be technically competent to choose between competing scientific theories.


Daubert’s reception at the state court level has been mixed. As precedent, Daubert is not binding on state courts, but the Frye rule that it replaced was also a federal pronouncement that, over time, found adoption in most state courts as the general standard for admissibility of scientific evidence. More-over, Rule 702 of the Federal Rules of Evidence has been adopted in thirty-eight states, and since Daubert relies in part on an expansive view of Rule 702, eventually most state courts will be required to reexamine their standards for admissibility of scientific evidence.

As the Daubert versus Frye debate continues at the state level, it will be the responsibility of the appellate courts, in those jurisdictions that have not resolved the issue, to provide a definitive standard of admissibility.


The Role of Appellate Courts in the Admissibility Debate. The rulings in both Daubert and Frye were pronouncements of appellate courts intended for application at the trial level.

Generally, trial courts operate as the primary force for resolving disputes and adjudicating criminal charges and appellate courts perform two distinct institutional functions: correction of error and definition of law.

While trial judges will continue to function as gatekeepers, either under Daubert’s express designation or under traditional standards, appellate judges, particularly at the state level, will also be required to fashion new standards of admissibility or opt to retain existing norms. In addition to the question of whether Frye should be abandoned as the cornerstone of admissibility of scientific evidence, a number of questions remain unanswered under Daubert. What is the relationship of Rule 703, which deals with the acceptability of the expert’s sources, to the reliability of the expert’s methods when examined under Rule 702? To what extent will the balancing test under Rule 403, measuring the probative value of evidence against its potential for prejudice, permit the trial judge to trump the process even where scientific evidence meets the threshold for admissibility under Daubert? These and other questions will require further refinement at the appellate level of many state courts in the years ahead.

The appellate process is essentially reactive in the sense that it responds to the record as constituted in the trial courts and to the issues as framed by the litigants. Thus, the primary focus will continue to be at the trial level, where offers of scientific evidence will confront the trial judge who is vested with the initial responsibility for acceptance or rejection of evidence. It is hoped that as definitional rules slowly emerge from the appellate level, trial judges will have available the standards necessary to address the proofs that continue to evolve from the world of science.


Is an Abuse of Discretion Standard Controlling? Daubert’s designation of trial judges as gatekeepers implicitly confers a large measure of discretion with respect to admissibility rulings. But as the Daubert debate continues and its proponents seek to expand its application to state courts, the initial rulings of trial judges on the standard of admissibility of scientific evidence, as opposed to the application of the standard to a specific proffer of evidence, will be subject to de novo review on appeal.

Even in the federal system, where Daubert’s general application is not open to question, appellate courts are applying a more rigorous standard than abuse of discretion as trial judges experiment with their newly conferred gatekeeper authority. At least one circuit court concerned about "the enormous power [of a trial court] to foreclose submission of a party’s case to a jury on the basis of a threshold determination of nonreliability of opinion evidence," has opted to take a "hard look" at the trial court’s exercise of discretion. The hard look approach by appellate courts may be tacit recognition that a trial judge with limited experience in scientific matters, struggling to resolve scientific disputes at the threshold of admissibility, may need the guidance of broad appellate review.


Conclusion. As genetic study and other areas of scientific inquiry advance, the judicial system will be challenged to accommodate this new knowledge while not abandoning the safeguards of relevancy and reliability. Both trial judges, as gatekeepers of admissibility, and appellate judges, as definers of the standards of proof, will be required to acquire new learning in fields unfamiliar to them. Unless these challenges are met, the judicial system may find itself unable to cope with the demands of modern litigation and the latest forensic techniques.

Joseph T. Walsh is a justice on the Delaware Supreme Court and previously served on the superior court and the court of chancery.

This article is an abridged and edited version of one that originally appeared on page 33 in The Judges’ Journal, Summer 1997 issue (36:3).

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