Scientific Evidence

When the courts began confronting new and more sophisticated scientific evidence in the late 1960s and early 1970s, they needed a legal test for determining admissibility. Three different approaches emerged. One treats the validity of the underlying principle and the validity of the technique as aspects of relevancy. A second approach, ultimately adopted by the U.S. Supreme Court, is known as the reliability test. (The relevancy and reliability approaches are discussed below.) A third approach, which requires the proponent of a novel technique to establish its general acceptance in the scientific community, is based on Frye v. United States, 293 F. 1013 (D.C. Cir. 1923), a federal case decided by the District of Columbia Circuit in 1923. In Frye the D.C. Circuit considered the admissibility of testimony based on the systolic blood pressure test, a precursor of the modern polygraph. The court announced that a novel scientific technique "must be sufficiently established to have gained general acceptance in the particular field in which it belongs" (p. 1014). The court found that the systolic test had "not yet gained such standing and scientific recognition among physiological and psychological authorities" (ibid.). Thus, under the Frye standard, it is not enough that a qualified individual expert, or even several experts, testify that a particular technique is valid. Frye imposes a special burden: the technique must be "generally" accepted by the relevant scientific community.

The Frye court's brief two-page opinion offered no explanation for adopting the "general acceptance" test. As a federal decision, it did not apply to state courts; for that matter, it was not binding on any of the other federal circuit courts. For the next five decades, Frye remained largely dormant; it was rarely cited, and then, mostly in polygraph cases. As late as 1972, a federal district court correctly observed that "[t]here is notably an absence of any discussion of the 'general acceptance' standard in federal decisions" (United States v. Zeiger, 350 F. Supp. 685, 687 n. 6 (D.D.C.), rev'd, 475 F.2d 1280 (D.C. Cir. 1972)).

This state of affairs was understandable. For most of the period between the rendition of Frye and the 1970s, the scientific techniques confronting the courts did not raise significant Frye issues—the admissibility of novel scientific evidence. A 1966 amendment to Federal Criminal Rule 16, which governs the pretrial disclosure of scientific reports in criminal litigation, provides some insight into the types of expert testimony used during this period. The accompanying committee note mentioned reports of "fingerprint and handwriting comparisons." Ballistics, blood tests, paint, fibers, and autopsies could be added to this list. None of these techniques presented Frye issues; they were traditional techniques, long accepted by the courts.

Over the years, the general acceptance standard gradually became the overwhelming majority rule in both federal and state courts until 1993 when the U.S. Supreme Court rejected Frye in Daubert v. Merrell Dow Pharmaceuticals, Inc. , 509 U.S. 579 (1993). By 1993, Frye had been applied to voiceprints, neutron activation, gunshot residue tests, fingerprints, bite mark comparisons, psycholinguistics, truth serum, scanning electron microscopic analysis, hypnosis, blood analysis, hair analysis, intoxication testing, instrumental analysis, and numerous other forensic techniques. Later, the Frye test would be applied to DNA evidence as well as to social science techniques such as the battered woman syndrome, rape trauma syndrome, child abuse accommodation syndrome, profile evidence, and psychiatric testimony.

Rationale. The stated justification for the general acceptance standard is that it tends to indirectly ensure the reliability of scientific evidence. The D.C. Circuit, the progenitor of the Frye test, later stated in rejecting voiceprint evidence that the "requirement of general acceptance in the scientific community assures that those most qualified to assess the general validity of a scientific method will have the determinative voice" (United States v. Addison, 498 F.2d 741, 743–44 (D.C. Cir. 1974)).

Application of Frye test. The Frye rule was not without its detractors. One criticism focused on the difficulties involved in applying the test. The general acceptance test requires a two-step analysis: first, identifying the field in which the underlying principle falls, and second, determining whether that principle has been generally accepted by members of the identified field. Neither step is free of difficulties.

The first step can be problematic. Many scientific techniques do not fall within the domain of a single academic discipline or professional field. Consequently, selecting the proper field may prove troublesome. For example, "voiceprint" analysis requires a knowledge of anatomy, physiology, physics, psychology, and linguistics. Similarly, DNA involves several disciplines—molecular biology, genetics, environmental biology, physical anthropology, evolutionary biology, population genetics, and statistics. The selection of the field, moreover, will often affect whether a novel technique satisfies the generalacceptance test. If polygraph examiners are selected as the relevant field, polygraph results would be admissible.

Once the relevant field has been identified, the second step requires determining whether the technique has been "generally accepted" by members of that field. The percentage of those in the field who must accept the technique has never been clearly specified. For instance, one court has defined general acceptance as "widespread; prevalent; extensive though not universal" (United States v. Zeiger, 350 F. Supp. 685, 688 (D.D.C.), rev'd, 475 F.2d 1280 (D.C. Cir. 1972)). Another court conceded that "a degree of scientific divergence of view is inevitable," without elaborating on how much divergence would be fatal to admissibility (Commonwealth v. Lykus, 327 N.E.2d 671, 678 n.6 (Mass. 1975)).

An additional issue arises in multiple-step procedures such as DNA profiling, which consists of a molecular biology component (declaring a match) and a population genetics component (statistical calculations). Are both aspects subject to the general-acceptance requirement? A related issue concerns subsequent developments or variants of a technique. For example, the general acceptance of stationary radar should not automatically lead to the admissibility of moving radar, in which the patrol car as well as the suspect car is in motion. Similarly, general acceptance of RFLP(DNA) does not mean that PCR(DNA), or even a particular type of PCR such as DQalpha, is necessarily admissible.

Moreover, some jurisdictions following Frye do not apply the general-acceptance test to all types of "scientific" evidence. For example, a California appellate court refused to apply the Frye test to bitemark comparisons (People v. Marx, 126 Cal. Rpt. 350, 355–56 (App. 1975)). The court reasoned that bite mark evidence did not require blind acceptance by the jury. The basis on which the expert reached his conclusions—models, photographs, and X rays—are shown to the trier of fact, and the trier could therefore independently second-guess the expert's conclusions. Similarly, the Arizona Supreme Court has ruled that the "Frye analysis is not applicable to footprints [comparisons]" (State v. Murray, 906 P.2d 542, 562 (Ariz. 1995), cert. denied, 518 U.S. 1011 (1996)). In short, many jurisdictions that profess adherence to Frye exempt some techniques from scrutiny under Frye.

Criticisms. In addition to the attacks concerning the difficulties of applying the Frye test discussed above, the test has been criticized on other grounds. Another criticism of the general-acceptance test is that it exacts too high a cost and often bars the admission of reliable evidence. Critics of Frye assert that the delay to permit the technique to win general acceptance "precludes too much relevant evidence for purposes of the fact determining process" (United States v. Sample, 378 F. Supp. 43, 53 (E.D. Pa. 1974)). In contrast, courts favoring the general acceptance test recognize its conservative nature but believe that this aspect does not exact an "unwarranted cost" (United States v. Addison, 498 F.2d 741, 743 (D.C. Cir. 1974)). The California Supreme Court has stated that the "primary advantage. . .of the Frye test lies in its essentially conservative nature" (People v. Kelly, 549 P.2d 1240, 1245 (Cal. 1976)). The criticism that the Frye test is too conservative begs a question. The question is not whether the Frye test is conservative (which it is), but whether other standards would better accomplish the objective of preventing the admission of unreliable scientific evidence.

Still another criticism of Frye is that it rests upon an invalid assumption, namely, that jurors are overwhelmed by scientific evidence. For example, in excluding voiceprint evidence under the Frye test, the D.C. Circuit asserted that scientific evidence may "assume a posture of mystic infallibility in the eyes of a jury of laymen" (United States v. Addison, 498 F.2d 741, 744 (D.C. Cir. 1974)). Commentators, however, have argued that the available empirical research on jury reaction to different types of scientific evidence does not support the D.C. Circuit's assertion (Rogers and Ewing; Imwinkelried, 1983).

Finally, "[p]erhaps the most important flaw in the Frye test is that by focusing attention on the general acceptance issue, the test obscures critical problems in the use of a particular technique" (Giannelli, 1980, p. 1226). There is a great diversity in the underlying bases of expert testimony, varying from the complexity of DNA to the social science—based research of rape trauma syndrome. The Frye "one-test-fits-all" approach is too blunt an instrument.