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Science, Forensic Science, Junk Science and Expert Opinion Testimony



The admissibility of expert opinion testimony in American courtrooms has seen significant developments in recent years. The earliest opinions dealing with the issue seem to have applied a "market place" test Ė that is: if a person could make a living doing what that personís occupation was, then the witness was probably an "expert" in it and, if an issue came up about which the witness could provide a special understanding to the jury, that witness would be permitted not only to testify to relevant factual knowledge about the case, but also offer opinion testimony as to the meaning of the witnessís testimony.

The first semi-formal test enunciated by an American court to more clearly define what constituted admissible expert testimony was in the case of Frye v. United States.

54 App.D.C. 46, 293 F. 1013 (D.C.Cir. 1923)

VAN ORSDEL, Associate Justice.

Appellant, defendant below, was convicted of the crime of murder in the second degree, and from the judgment prosecutes this appeal.

A single assignment of error is presented for our consideration. In the course of the trial counsel for defendant offered an expert witness to testify to the result of a deception test made upon defendant. The test is described as the systolic blood pressure deception test. It is asserted that blood pressure is influenced by change in the emotions of the witness, and that the systolic blood pressure rises are brought about by nervous impulses sent to the sympathetic branch of the autonomic nervous system. Scientific experiments, it is claimed, have demonstrated that fear, rage, and pain always produce a rise of systolic blood pressure, and that conscious deception or falsehood, concealment of facts, or guilt of crime, accompanied by fear of detection when the person is under examination, raises the systolic blood pressure in a curve, which corresponds exactly to the struggle going on in the subject's mind, between fear and attempted control of that fear, as the examination touches the vital points in respect of which he is attempting to deceive the examiner.

In other words, the theory seems to be that truth is spontaneous, and comes without conscious effort, while the utterance of a falsehood requires a conscious effort, which is reflected in the blood pressure. The rise thus produced is easily detected and distinguished from the rise produced by mere fear of the examination itself. In the former instance, the pressure rises higher than in the latter, and is more pronounced as the examination proceeds, while in the latter case, if the subject is telling the truth, the pressure registers highest at the beginning of the examination, and gradually diminishes as the examination proceeds.

Prior to the trial defendant was subjected to this deception test, and counsel offered the scientist who conducted the test as an expert to testify to the results obtained. The offer was objected to by counsel for the government, and the court sustained the objection. Counsel for defendant then offered to have the proffered witness conduct a test in the presence of the jury. This also was denied.

Counsel for defendant, in their able presentation of the novel question involved, correctly state in their brief that no cases directly in point have been found. The broad ground, however, upon which they plant their case, is succinctly stated in their brief as follows:

'The rule is that the opinions of experts or skilled witnesses are admissible in evidence in those cases in which the matter of inquiry is such that inexperienced persons are unlikely to prove capable of forming a correct judgment upon it, for the reason that the subject-matter so far partakes of a science, art, or trade as to require a previous habit or experience or study in it, in order to acquire a knowledge of it. When the question involved does not lie within the range of common experience or common knowledge, but requires special experience or special knowledge, then the opinions of witnesses skilled in that particular science, art, or trade to which the question relates are admissible in evidence.'

Numerous cases are cited in support of this rule. Just when a scientific principle or discovery crosses the line between the experimental and demonstrable stages is difficult to define. Somewhere in this twilight zone the evidential force of the principle must be recognized, and while courts will go a long way in admitting expert testimony deduced from a well-recognized scientific principle or discovery, the thing from which the deduction is made must be sufficiently established to have gained general acceptance in the particular field in which it belongs.

We think the systolic blood pressure deception test has not yet gained such standing and scientific recognition among physiological and psychological authorities as would justify the courts in admitting expert testimony deduced from the discovery, development, and experiments thus far made.

The judgment is affirmed.


The Frye test ultimately became the general test for the admissibility of novel "scientific" evidence in criminal cases. It became the law in most states and also the federal circuits.

After the adoption of the Federal Rules of Evidence in 1975, some cases suggested that the federal rules had done away with the Frye test. Federal Rule 702 on the "Testimony by Experts" stated:

"If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise." [This was the rule until December 1, 2000. As of that date, an amendment was added to the rule after "otherwise" as follows:

", if (1) the testimony is based upon sufficient facts or data, (2) the testimony is the product of reliable principles and methods, and (3) the witness has applied the principles and methods reliably to the facts of the case." This amendment sought to incorporate the requirements of the Daubert case, discussed infra.

Some federal courts held, in the aftermath of the adoption of the Federal Rules of Evidence, that the Rules were not as demanding as the Frye test was said to be, and that therefore opinion evidence that even somewhat helpful, though not necessarily of the greatest reliability, would be admissible. This approach came to be referred to as a "general relevance" rule. Many circuits, however, believed that the Frye rule had survived the adoption of the Federal Rules of Evidence and was not inconsistent with Rule 702. The same approach was being followed by states that had adopted state rules of evidence patterned closely upon the federal rules. Thus, at the onset of the last decade of the past century, Frye clearly was still the majority rule throughout the United States.

In 1993, however, the issue of whether the adoption of the federal rules of evidence had done away with the Frye rule, when it came to admitting expert opinion testimony, came squarely before the Supreme Court in the case of Daubert v. Merrell Dow Pharmaceuticals.

509 U.S. 579, 113 S. Ct. 2786, 125 L.Ed.2d 469 (1993)

[Some footnotes were omitted; the remaining ones were renumbered.]

Justice BLACKMUN delivered the opinion of the Court.

In this case we are called upon to determine the standard for admitting expert scientific testimony in a federal trial.


Petitioners Jason Daubert and Eric Schuller are minor children born with serious birth defects. They and their parents sued respondent in California state court, alleging that the birth defects had been caused by the mothers' ingestion of Bendectin, a prescription antinausea drug marketed by respondent. Respondent removed the suits to federal court on diversity grounds.

After extensive discovery, respondent moved for summary judgment, contending that Bendectin does not cause birth defects in humans and that petitioners would be unable to come forward with any admissible evidence that it does. In support of its motion, respondent submitted an affidavit of Steven H. Lamm, physician and epidemiologist, who is a well-credentialed expert on the risks from exposure to various chemical substances.1  Doctor Lamm stated that he had reviewed all the literature on Bendectin and human birth defects--more than 30 published studies involving over 130,000 patients. No study had found Bendectin to be a human teratogen (i.e., a substance capable of causing malformations in fetuses). On the basis of this review, Doctor Lamm concluded that maternal use of Bendectin during the first trimester of pregnancy has not been shown to be a risk factor for human birth defects.

Petitioners did not (and do not) contest this characterization of the published record regarding Bendectin. Instead, they responded to respondent's motion with the testimony of eight experts of their own, each of whom also possessed impressive credentials.2  These experts had concluded that Bendectin can cause birth defects. Their conclusions were based upon "in vitro" (test tube) and "in vivo" (live) animal studies that found a link between Bendectin and malformations; pharmacological studies of the chemical structure of Bendectin that purported to show similarities between the structure of the drug and that of other substances known to cause birth defects; and the "reanalysis" of previously published epidemiological (human statistical) studies.

The District Court granted respondent's motion for summary judgment. The court stated that scientific evidence is admissible only if the principle upon which it is based is "sufficiently established to have general acceptance in the field to which it belongs.", quoting United States v. Kilgus, 571 F.2d 508, 510 (CA9 1978). The court concluded that petitioners' evidence did not meet this standard. Given the vast body of epidemiological data concerning Bendectin, the court held, expert opinion which is not based on epidemiological evidence is not admissible to establish causation. Thus, the animal- cell studies, live-animal studies, and chemical-structure analyses on which petitioners had relied could not raise by themselves a reasonably disputable jury issue regarding causation. Petitioners' epidemiological analyses, based as they were on recalculations of data in previously published studies that had found no causal link between the drug and birth defects, were ruled to be inadmissible because they had not been published or subjected to peer review.

The United States Court of Appeals for the Ninth Circuit affirmed. Citing Frye v. United States, the court stated that expert opinion based on a scientific technique is inadmissible unless the technique is "generally accepted" as reliable in the relevant scientific community. The court declared that expert opinion based on a methodology that diverges "significantly from the procedures accepted by recognized authorities in the field ... cannot be shown to be 'generally accepted as a reliable technique.' " . . .

The court emphasized that other Courts of Appeals considering the risks of Bendectin had refused to admit reanalyses of epidemiological studies that had been neither published nor subjected to peer review. Those courts had found unpublished reanalyses particularly problematic in light of the massive weight of the original published studies supporting [respondent's] position, all of which had undergone full scrutiny from the scientific community. Contending that reanalysis is generally accepted by the scientific community only when it is subjected to verification and scrutiny by others in the field, the Court of Appeals rejected petitioners' reanalyses as "unpublished, not subjected to the normal peer review process and generated solely for use in litigation." The court concluded that petitioners' evidence provided an insufficient foundation to allow admission of expert testimony that Bendectin caused their injuries and, accordingly, that petitioners could not satisfy their burden of proving causation at trial.

We granted certiorari, in light of sharp divisions among the courts regarding the proper standard for the admission of expert testimony. . . .



In the 70 years since its formulation in the Frye case, the "general acceptance" test has been the dominant standard for determining the admissibility of novel scientific evidence at trial. Although under increasing attack of late, the rule continues to be followed by a majority of courts, including the Ninth Circuit.

The Frye test has its origin in a short and citation-free 1923 decision concerning the admissibility of evidence derived from a systolic blood pressure deception test, a crude precursor to the polygraph machine. . . .

The merits of the Frye test have been much debated, and scholarship on its proper scope and application is legion. Petitioners' primary attack, however, is not on the content but on the continuing authority of the rule. They contend that the Frye test was superseded by the adoption of the Federal Rules of Evidence. We agree.

We interpret the legislatively enacted Federal Rules of Evidence as we would any statute. Rule 402 provides the baseline:

"All relevant evidence is admissible, except as otherwise provided by the Constitution of the United States, by Act of Congress, by these rules, or by other rules prescribed by the Supreme Court pursuant to statutory authority. Evidence which is not relevant is not admissible."

"Relevant evidence" is defined as that which has "any tendency to make the existence of any fact that is of consequence to the determination of the action more probable or less probable than it would be without the evidence." Rule 401. The Rule's basic standard of relevance thus is a liberal one.

Frye, of course, predated the Rules by half a century. In United States v. Abel, 469 U.S. 45, 105 S.Ct. 465, 83 L.Ed.2d 450 (1984), we considered the pertinence of background common law in interpreting the Rules of Evidence. We noted that the Rules occupy the field, but, quoting Professor Cleary, the Reporter, explained that the common law nevertheless could serve as an aid to their application: . . .

We found the common-law precept at issue in the Abel case entirely consistent with Rule 402's general requirement of admissibility, and considered it unlikely that the drafters had intended to change the rule. In Bourjaily v. United States, 483 U.S. 171, 107 S.Ct. 2775, 97 L.Ed.2d 144 (1987), on the other hand, the Court was unable to find a particular common-law doctrine in the Rules, and so held it superseded.

Here there is a specific Rule that speaks to the contested issue. Rule 702, governing expert testimony, provides:

"If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise."

Nothing in the text of this Rule establishes "general acceptance" as an absolute prerequisite to admissibility. Nor does respondent present any clear indication that Rule 702 or the Rules as a whole were intended to incorporate a "general acceptance" standard. The drafting history makes no mention of Frye, and a rigid "general acceptance" requirement would be at odds with the liberal thrust of the Federal Rules and their general approach of relaxing the traditional barriers to opinion testimony. . . . Given the Rules' permissive backdrop and their inclusion of a specific rule on expert testimony that does not mention "general acceptance," the assertion that the Rules somehow assimilated Frye is unconvincing. Frye made "general acceptance" the exclusive test for admitting expert scientific testimony. That austere standard, absent from, and incompatible with, the Federal Rules of Evidence, should not be applied in federal trials.


That the Frye test was displaced by the Rules of Evidence does not mean, however, that the Rules themselves place no limits on the admissibility of purportedly scientific evidence.3  Nor is the trial judge disabled from screening such evidence. To the contrary, under the Rules the trial judge must ensure that any and all scientific testimony or evidence admitted is not only relevant, but reliable.

The primary locus of this obligation is Rule 702, which clearly contemplates some degree of regulation of the subjects and theories about which an expert may testify. "If scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue" an expert "may testify thereto." (Emphasis added.) The subject of an expert's testimony must be "scientific ... knowledge."4  The adjective "scientific" implies a grounding in the methods and procedures of science. Similarly, the word "knowledge" connotes more than subjective belief or unsupported speculation. The term "applies to any body of known facts or to any body of ideas inferred from such facts or accepted as truths on good grounds." Webster's Third New International Dictionary 1252 (1986). Of course, it would be unreasonable to conclude that the subject of scientific testimony must be "known" to a certainty; arguably, there are no certainties in science. See, e.g., Brief for Nicolaas Bloembergen et al. as Amici Curiae 9 ("Indeed, scientists do not assert that they know what is immutably 'true'--they are committed to searching for new, temporary, theories to explain, as best they can, phenomena"); Brief for American Association for the Advancement of Science et al. as Amici Curiae 7-8 ("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" (emphasis in original)). But, in order to qualify as "scientific knowledge," an inference or assertion must be derived by the scientific method. Proposed testimony must be supported by appropriate validation--i.e., "good grounds," based on what is known. In short, the requirement that an expert's testimony pertain to "scientific knowledge" establishes a standard of evidentiary reliability.5

Rule 702 further requires that the evidence or testimony "assist the trier of fact to understand the evidence or to determine a fact in issue."6  This condition goes primarily to relevance. Expert testimony which does not relate to any issue in the case is not relevant and, ergo, non-helpful.. ..This consideration has been aptly described by Judge Becker as one of "fit." "Fit" is not always obvious, and scientific validity for one purpose is not necessarily scientific validity for other, unrelated purposes. See Starrs, Frye v. United States Restructured and Revitalized: A Proposal to Amend Federal Evidence Rule 702, 26 Jurimetrics J. 249, 258 (1986). The study of the phases of the moon, for example, may provide valid scientific "knowledge" about whether a certain night was dark, and if darkness is a fact in issue, the knowledge will assist the trier of fact. However (absent creditable grounds supporting such a link), evidence that the moon was full on a certain night will not assist the trier of fact in determining whether an individual was unusually likely to have behaved irrationally on that night. Rule 702's "helpfulness" standard requires a valid scientific connection to the pertinent inquiry as a precondition to admissibility.

That these requirements are embodied in Rule 702 is not surprising. Unlike an ordinary witness, see Rule 701, an expert is permitted wide latitude to offer opinions, including those that are not based on firsthand knowledge or observation. See Rules 702 and 703. Presumably, this relaxation of the usual requirement of firsthand knowledge--a rule which represents "a 'most pervasive manifestation' of the common law insistence upon 'the most reliable sources of information,' " Advisory Committee's Notes on Fed.Rule Evid. 602, 28 U.S.C.App., p. 755 (citation omitted)--is premised on an assumption that the expert's opinion will have a reliable basis in the knowledge and experience of his discipline.


Faced with a proffer of expert scientific testimony, then, the trial judge must determine at the outset, pursuant to Rule 104(a), whether the expert is proposing to testify to (1) scientific knowledge that (2) will assist the trier of fact to understand or determine a fact in issue.

This entails a preliminary assessment of whether the reasoning or methodology underlying the testimony is scientifically valid and of whether that reasoning or methodology properly can be applied to the facts in issue. We are confident that federal judges possess the capacity to undertake this review. Many factors will bear on the inquiry, and we do not presume to set out a definitive checklist or test. But some general observations are appropriate.

Ordinarily, a key question to be answered in determining whether a theory or technique is scientific knowledge that will assist the trier of fact will be whether it can be (and has been) tested. "Scientific methodology today is based on generating hypotheses and testing them to see if they can be falsified; indeed, this methodology is what distinguishes science from other fields of human inquiry." Green 645. See also C. Hempel, Philosophy of Natural Science 49 (1966) ("[T]he statements constituting a scientific explanation must be capable of empirical test"); K. Popper, Conjectures and Refutations: The Growth of Scientific Knowledge 37 (5th ed. 1989) ("[T]he criterion of the scientific status of a theory is its falsifiability, or refutability, or testability") (emphasis deleted).

Another pertinent consideration is whether the theory or technique has been subjected to peer review and publication. Publication (which is but one element of peer review) is not a sine qua non of admissibility; it does not necessarily correlate with reliability, see S. Jasanoff, The Fifth Branch: Science Advisors as Policymakers 61-76 (1990), and in some instances well-grounded but innovative theories will not have been published, see Horrobin, The Philosophical Basis of Peer Review and the Suppression of Innovation, 263 JAMA 1438 (1990). Some propositions, moreover, are too particular, too new, or of too limited interest to be published. But submission to the scrutiny of the scientific community is a component of "good science," in part because it increases the likelihood that substantive flaws in methodology will be detected. See J. Ziman, Reliable Knowledge: An Exploration of the Grounds for Belief in Science 130-133 (1978); Relman & Angell, How Good Is Peer Review?, 321 New Eng.J.Med. 827 (1989). The fact of publication (or lack thereof) in a peer reviewed journal thus will be a relevant, though not dispositive, consideration in assessing the scientific validity of a particular technique or methodology on which an opinion is premised.

Additionally, in the case of a particular scientific technique, the court ordinarily should consider the known or potential rate of error, see, e.g., United States v. Smith, 869 F.2d 348, 353-354 (CA7 1989) (surveying studies of the error rate of spectrographic voice identification technique), and the existence and maintenance of standards controlling the technique's operation, see United States v. Williams, 583 F.2d 1194, 1198 (CA2 1978) (noting professional organization's standard governing spectrographic analysis), cert. denied, 439 U.S. 1117, 99 S.Ct. 1025, 59 L.Ed.2d 77 (1979).

Finally, "general acceptance" can yet have a bearing on the inquiry. A "reliability assessment does not require, although it does permit, explicit identification of a relevant scientific community and an express determination of a particular degree of acceptance within that community." United States v. Downing, 753 F.2d, at 1238. . . . Widespread acceptance can be an important factor in ruling particular evidence admissible, and a known technique which has been able to attract only minimal support within the community, may properly be viewed with skepticism.

The inquiry envisioned by Rule 702 is, we emphasize, a flexible one.7 Its overarching subject is the scientific validity and thus the evidentiary relevance and reliability--of the principles that underlie a proposed submission. The focus, of course, must be solely on principles and methodology, not on the conclusions that they generate.

Throughout, a judge assessing a proffer of expert scientific testimony under Rule 702 should also be mindful of other applicable rules. Rule 703 provides that expert opinions based on otherwise inadmissible hearsay are to be admitted only if the facts or data are "of a type reasonably relied upon by experts in the particular field in forming opinions or inferences upon the subject." Rule 706 allows the court at its discretion to procure the assistance of an expert of its own choosing. Finally, Rule 403 permits the exclusion of relevant evidence "if its probative value is substantially outweighed by the danger of unfair prejudice, confusion of the issues, or misleading the jury...." Judge Weinstein has explained: "Expert evidence can be both powerful and quite misleading because of the difficulty in evaluating it. Because of this risk, the judge in weighing possible prejudice against probative force under Rule 403 of the present rules exercises more control over experts than over lay witnesses." Weinstein, 138 F.R.D., at 632.


We conclude by briefly addressing what appear to be two underlying concerns of the parties and amici in this case. Respondent expresses apprehension that abandonment of "general acceptance" as the exclusive requirement for admission will result in a "free-for-all" in which befuddled juries are confounded by absurd and irrational pseudoscientific assertions. In this regard respondent seems to us to be overly pessimistic about the capabilities of the jury and of the adversary system generally. Vigorous cross-examination, presentation of contrary evidence, and careful instruction on the burden of proof are the traditional and appropriate means of attacking shaky but admissible evidence. Additionally, in the event the trial court concludes that the scintilla of evidence presented supporting a position is insufficient to allow a reasonable juror to conclude that the position more likely than not is true, the court remains free to direct a judgment, Fed.Rule Civ.Proc. 50(a), and likewise to grant summary judgment, Fed.Rule Civ.Proc. 56. Cf., e.g., Turpin v. Merrell Dow Pharmaceuticals, Inc., 959 F.2d 1349 (CA6) (holding that scientific evidence that provided foundation for expert testimony, viewed in the light most favorable to plaintiffs, was not sufficient to allow a jury to find it more probable than not that defendant caused plaintiff's injury), cert. denied, 506 U.S. 826, 113 S.Ct. 84, 121 L.Ed.2d 47 (1992); Brock v. Merrell Dow Pharmaceuticals, Inc., 874 F.2d 307 (CA5 1989) (reversing judgment entered on jury verdict for plaintiffs because evidence regarding causation was insufficient), modified, 884 F.2d 166 (CA5 1989), cert. denied, 494 U.S. 1046, 110 S.Ct. 1511, 108 L.Ed.2d 646 (1990); Green 680-681. These conventional devices, rather than wholesale exclusion under an uncompromising "general acceptance" test, are the appropriate safeguards where the basis of scientific testimony meets the standards of Rule 702.

Petitioners and, to a greater extent, their amici exhibit a different concern. They suggest that recognition of a screening role for the judge that allows for the exclusion of "invalid" evidence will sanction a stifling and repressive scientific orthodoxy and will be inimical to the search for truth. See, e.g., Brief for Ronald Bayer et al. as Amici Curiae. It is true that open debate is an essential part of both legal and scientific analyses. Yet there are important differences between the quest for truth in the courtroom and the quest for truth in the laboratory. Scientific conclusions are subject to perpetual revision. Law, on the other hand, must resolve disputes finally and quickly. The scientific project is advanced by broad and wide-ranging consideration of a multitude of hypotheses, for those that are incorrect will eventually be shown to be so, and that in itself is an advance. Conjectures that are probably wrong are of little use, however, in the project of reaching a quick, final, and binding legal judgment--often of great consequence--about a particular set of events in the past. We recognize that, in practice, a gatekeeping role for the judge, no matter how flexible, inevitably on occasion will prevent the jury from learning of authentic insights and innovations. That, nevertheless, is the balance that is struck by Rules of Evidence designed not for the exhaustive search for cosmic understanding but for the particularized resolution of legal disputes.


To summarize: "General acceptance" is not a necessary precondition to the admissibility of scientific evidence under the Federal Rules of Evidence, but the Rules of Evidence--especially Rule 702--do assign to the trial judge the task of ensuring that an expert's testimony both rests on a reliable foundation and is relevant to the task at hand. Pertinent evidence based on scientifically valid principles will satisfy those demands.

The inquiries of the District Court and the Court of Appeals focused almost exclusively on "general acceptance," as gauged by publication and the decisions of other courts. Accordingly, the judgment of the Court of Appeals is vacated, and the case is remanded for further proceedings consistent with this opinion.

It is so ordered.

Chief Justice REHNQUIST, with whom Justice STEVENS joins, concurring in part and dissenting in part.

The petition for certiorari in this case presents two questions: first, whether the rule of Frye v. United States, remains good law after the enactment of the Federal Rules of Evidence; and second, if Frye remains valid, whether it requires expert scientific testimony to have been subjected to a peer review process in order to be admissible. The Court concludes, correctly in my view, that the Frye rule did not survive the enactment of the Federal Rules of Evidence, and I therefore join Parts I and II-A of its opinion. The second question presented in the petition for certiorari necessarily is mooted by this holding, but the Court nonetheless proceeds to construe Rules 702 and 703 very much in the abstract, and then offers some "general observations."

"General observations" by this Court customarily carry great weight with lower federal courts, but the ones offered here suffer from the flaw common to most such observations--they are not applied to deciding whether particular testimony was or was not admissible, and therefore they tend to be not only general, but vague and abstract. This is particularly unfortunate in a case such as this, where the ultimate legal question depends on an appreciation of one or more bodies of knowledge not judicially noticeable, and subject to different interpretations in the briefs of the parties and their amici. Twenty-two amicus briefs have been filed in the case, and indeed the Court's opinion contains no fewer than 37 citations to amicus briefs and other secondary sources.

The various briefs filed in this case are markedly different from typical briefs, in that large parts of them do not deal with decided cases or statutory language--the sort of material we customarily interpret. Instead, they deal with definitions of scientific knowledge, scientific method, scientific validity, and peer review--in short, matters far afield from the expertise of judges. This is not to say that such materials are not useful or even necessary in deciding how Rule 703 should be applied; but it is to say that the unusual subject matter should cause us to proceed with great caution in deciding more than we have to, because our reach can so easily exceed our grasp.

But even if it were desirable to make "general observations" not necessary to decide the questions presented, I cannot subscribe to some of the observations made by the Court. In Part II-B, the Court concludes that reliability and relevancy are the touchstones of the admissibility of expert testimony. Federal Rule of Evidence 402 provides, as the Court points out, that "[e]vidence which is not relevant is not admissible." But there is no similar reference in the Rule to "reliability." The Court constructs its argument by parsing the language "[i]f scientific, technical, or other specialized knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, ... an expert ... may testify thereto...." Fed.Rule Evid. 702. It stresses that the subject of the expert's testimony must be "scientific ... knowledge," and points out that "scientific" "implies a grounding in the methods and procedures of science" and that the word "knowledge" "connotes more than subjective belief or unsupported speculation." From this it concludes that "scientific knowledge" must be "derived by the scientific method." Proposed testimony, we are told, must be supported by "appropriate validation." Indeed, in [a] footnote . . . , the Court decides that "[i]n a case involving scientific evidence, evidentiary reliability will be based upon scientific validity." (emphasis in original).

Questions arise simply from reading this part of the Court's opinion, and countless more questions will surely arise when hundreds of district judges try to apply its teaching to particular offers of expert testimony. Does all of this dicta apply to an expert seeking to testify on the basis of "technical or other specialized knowledge"--the other types of expert knowledge to which Rule 702 applies--or are the "general observations" limited only to "scientific knowledge"? What is the difference between scientific knowledge and technical knowledge; does Rule 702 actually contemplate that the phrase "scientific, technical, or other specialized knowledge" be broken down into numerous subspecies of expertise, or did its authors simply pick general descriptive language covering the sort of expert testimony which courts have customarily received? The Court speaks of its confidence that federal judges can make a "preliminary assessment of whether the reasoning or methodology underlying the testimony is scientifically valid and of whether that reasoning or methodology properly can be applied to the facts in issue." The Court then states that a "key question" to be answered in deciding whether something is "scientific knowledge" "will be whether it can be (and has been) tested." Following this sentence are three quotations from treatises, which not only speak of empirical testing, but one of which states that the " 'criterion of the scientific status of a theory is its falsifiability, or refutability, or testability,' "

I defer to no one in my confidence in federal judges; but I am at a loss to know what is meant when it is said that the scientific status of a theory depends on its "falsifiability," and I suspect some of them will be, too.

I do not doubt that Rule 702 confides to the judge some gatekeeping responsibility in deciding questions of the admissibility of proffered expert testimony. But I do not think it imposes on them either the obligation or the authority to become amateur scientists in order to perform that role. I think the Court would be far better advised in this case to decide only the questions presented, and to leave the further development of this important area of the law to future cases.

The definition of "scientific knowledge" given by the Supreme Court in Daubert was drawn from the physical sciences. It clearly did not appropriately apply to all of the disciplines that had, heretofore, been said to yield "scientific" evidence in the courts.

This, of course, caused people to raise a lot of questions:

(1) Was any specialty that could not satisfy the "scientific knowledge" definition in Daubert non-scientific, perhaps "junk science"? (E.g., psychiatry; forensic pathology, many crime laboratory techniques.)

(2) Do the Daubert factors for judging whether we are dealing with "scientific knowledge" apply only to novel areas of endeavor, or must they also be applied to disciplines that have already long been judicially acceptance? (E.g., handwriting comparisons; hair comparisons; fingerprints; serology; firearms identifications {"ballistics" evidence])

(3) Was the Supreme Courtís definition of "science" perhaps flawed, or inappropriate?

(4) Should the Daubert factors, which clearly were inapplicable to some disciplines that had traditionally been referred to as yielding "scientific" evidence, be applied to all forms of expert testimony, even those not based on "science"?

Courts were very inconsistent in answering these questions, which forced the Supreme Court to clarify its Daubert decision. It did so in 1999 in the case of Kumho Tire v. Carmichael, 526 U.S. 137, 119 S.Ct. 1167, 143 L.Ed.2d 238 (1999).

In the interim, however, the Court ha d decided another Daubert case. In 1997, in General Electric v. Joiner, 522 U.S. 136 (1997), the Court amplified its Daubert holding by adding that in reviewing the decision of a trial court to either admit or deny admission of certain expert testimony, whether on the issue of the judge's determination of reliability/ unreliability, or on the ultimate conclusion reached by an expert, a court of appeals must use an abuse-of-discretion standard.

To the question whether a Daubert inquiry would be required when a court was dealing with non-scientific expert opinion evidence, or when a particular technique already had gained widespread judicial acceptance, the Courtís 1999 Kumho Tire decision gave an unequivocal "yes" answer.

In Kumho Tire, the Court held that the Daubert factors may apply to the

opinion testimony of non-scientist expert witnesses. The Kumho Tire case was a diversity action against the maker and distributor of an automobile tire. The tire had blown out, which caused the minivan on which it was mounted to turn over. In the accident, one passenger died and others were injured.

The plaintiffs sought to make their case through the testimony of a tire failure analyst who wanted to testify that a defect in the tire's design or manufacture caused the blowout. The defendants sought to exclude the expert's evidence on the ground that the methodology did not satisfy Federal Rule of Evidence 702's requirements. The district court, applying the Daubert factors, agreed with defendants and granted the motion. It also entered summary judgment for defendants. While there were some intermediate procedural steps, the case ultimately reached the United States Supreme Court on the issue of whether Daubert applied only to expert evidence that was based on scientific knowledge.

Without equivocation, the Court held that the obligation imposed on trial judges by Daubert to act as gatekeepers applies not only to scientific testimony, but it applies to all expert opinion testimony. In order to fulfill its gatekeeping responsibility, a court may use the factors identified in Daubert IF they can be appropriately utilized to determine reliability of either the underlying technique or the expert's conclusions. But since Daubert clearly stipulated that the inquiry it asks trial judges to undertake is a flexible one, the gatekeeping function of necessity must be tied to the particular facts of a case. Thus, the factors identified in Daubert are not supposed to be talismanic, nor do they constitute a definitive checklist or litmus test.

In this newest decision, the Court continued to grant trial judges a broad latitude of discretion. The Court permits trial judges to apply any and all useful factors, whether identified in Daubert or elsewhere, that will assist the tribunal in making a determination of reliability of proffered evidence as deemed appropriate in the particular case.


An inquiry about whether we are dealing with "junk science" requires that we first define the descriptive labels we use.

In Daubert, the Supreme Court defined "scientific knowledge," and by inference also what constitutes "science." But the Courtís use of Karl Popperís definition [Karl Popper, CONJECTURES AND REFUTATIONS: THE GROWTH OF SCIENTIFIC KNOWLEDGE, 5th ed. 1989] has criticized as being "outmoded" even when it was announced (Dr. Walter F. Rowe, The George Washington University, lectured on "Daubertís Obsolete Model of Science" in 1997; his lecture and premise is discussed in Andre A. Moenssens, "Handwriting Identification in the Post-Daubert World," 66 UMKC Law Rev. 251, at 286-287 (1997). Many other scientists have spoken in a similar vein.

What is "Forensic Science." The American Academy of Forensic Sciences, the leading association of forensic scientists in the world, defines "forensic science":

"Forensic science is the application of scientific principles and technological practices to the purposes of justice in the study and resolution of criminal, civil, and regulatory issues."

This definition is not particularly helpful, in that it does not clarify what constitutes "scientific principles." Whatís more, it also seems to embody, under the "forensic science" mantle, "technological practices" which might not fit the label given by most people who have sought to define "science." The label forensic science has no real meaning for some "scientists." Dr. Andrew Twaddle, Sociology, UMC, hazards the guess that it is the use of science, or the tools of science, to solve questions of guilt or innocence. If so, it would not qualify as "science" by most definitions.

Dr. Brian DeFacio, Professor of Physics, UMKC, divides "science" into "hard science" and "practical science." Defining "hard science" much like Karl Popper did, he states that hard science must give "results that are reproducible; these results are falsifiable by empirical process in identifying the case where the theory does not work; and its results have predictive power. Physics, astrophysics, chemistry, some areas of geology and engineering, and neurophysiology are hard sciences in this sense. He suggests that classical biology, classical geology and classical astronomy are primitive in that the fields consist merely of naming things. Mathematics, he states, is not empirically based but is based on logic, with the exception of applied mathematics in which mathematical concepts are used to solve real problems.

He contrasts "practical science" in that it has some but not all of the properties of hard science. He places forensic science (undefined as to which sub-disciplines he intends to include herein) in that category. Psychology and sociology are not in the hard science category because they have no predictability and are not falsifiable. Medicine may have some elements of predictability, but since the physicianís interaction with the patient is a vital part of this science, it also has elements of art.

Are all opinions by experts, arrived at by diagnostic means, "art" rather than "science"?

Dr. DeFazio defines "junk science" as having none of the qualities of hard science, and engaging in manipulating inapplicable statistics and opinion polls "data" to make it appear as if the data is quantitative. Junk science, he states, it not reproducible, predictable, or falsifiable. He places certain areas of psychology and sociology, as well as handwriting analysis, in this category.

Peter William Huber popularized the term "junk science" when he published his book, GALILEOíS REVENGE: JUNK SCIENCE IN THE COURTROOM, in 1991. (It was actually an expansion of an article he had previously published in a popular magazine.) Huber states: "The art of junk science is to brush away just enough detail to reach desired conclusions, while preserving enough to maintain an aura of authoritative science." (Huber, by the way, is a lawyer, not a scientist!)


The identification of the author of a questioned handwriting by a comparison with samples of the known handwriting of individuals.

The identification of the perpetrator of a crime by comparing a latent fingerprint found at a crime scene against the fingerprints of known individuals.

The determination of the "time of death" by forensic pathologists examining a sudden and unexplained death.

The identification of the person who inflicted a bitemark upon a victim of a crime by comparison of the mark with dental information obtained from known individuals.

The identification of a bullet as having been fired by a given weapon.

The identification of a tool that may have been used to produce a mark found at the scene of a crime.

The identification of the person who has left or may have left a certain biological specimen by serological methods or by DNA analysis.



1. EAR PRINT IDENTIFICATION, performed by a few fingerprint experts, document experts, toolmark examiners. Was actually used in three American trials: the first case no one heard of; the second one in Florida some 10-15 years ago where, after a Frye hearing, the defenseís motion in limine to exclude was granted Ė thus, the evidence of the "identification" didnít get introduced at trial; and the third the case of State v. Kunze, in the State of Washington in 1998.

Kunze: Motion in limine to exclude identification evidence denied; evidence or earprint identification used at trial; conviction obtained. Conviction reversed on appeal. See: State v. Kunze, 97 Wash.App. 832, 988 P.2d 977 (1999). See also, related stories on my Web Site:

"Court Holds Earprint Identification Not Generally Accepted In Scientific Community," at

"Ear Identification Research," at

"Are Dutch Ears Different From American Ears," by Toby Egan, at

"Ear Identification Based On Surveillance Cameraís Images," by Dr. Hoogstrate, et al., at

"Ear Identification In The News Again . . . This time itís ear photographs," at

The sole British case where earprint identification evidence was used is now pending on appeal.

The Dutch case of an identification by ear photographs also reversed on appeal.

2. FOOTPRINT "CINDERELLA ANALYSIS" IDENTIFICATION. Identifying the wearer of a pair of shoes from a study of the insole, dubbed "Cinderella Analysis." The prowess of the late Dr. Louise Robbins, anthropologist, who was the only expert in the country to be able to do this, lead to convictions and appeals in dozens of cases. One of the cases even reached the United States Supreme Court as Buckley v. Fitzsimmons, 113 S.Ct. 2606 (1993). A complete discussion of this sorry episode in forensic science, and the appellate court cases dealing with this "technique," can be found in Moenssens, Starrs, Henderson and Inbay, SCIENTIFIC EVIDENCE IN CIVIL AND CRIMINAL CASES, 4TH ed. 1995, at pp. 614-620 & pp. 1049-1052.

3. LIP PRINT IDENTIFICATION. The first appellate (and perhaps the only trial court) case in the United States admitting lip print evidence to identify the perpetrator of a crime, and upholding said admission, occurred in Illinois in 1999. See, People v. Davis, 304 Ill.App.3d 427, 710 N.E.2d 1251 (2d. Dist. 1999), appeal denied 185 Ill.2d 639, 720 N.E.2d 1097 (1999). The case is currently on review, again. See the short story on this at "Lip Print Identification Anyone?" at>10.html

Q. What about "Lipsology"?

4. Miscellaneous "Junk" Science techniques featured in the occasional literature or news media the last two years: Identifying by Flexure Creases; Cow and Sheep Nose Print Identification; Elbow Prints, Crano-facial identification [Lombrosoís Revenge?], Eye Iris Identification, etc.