OPINION OF THE COURT
BECKER, Circuit Judge.
This case presents a question of first impression in this Circuit — whether Fed.R.Evid. 702 permits a defendant in a criminal prosecution to adduce, from an expert in the field of human perception and memory, testimony concerning the reliability of eyewitness identifications. The district court refused to admit the testimony of a psychologist offered by the defendant, apparently because the court believed that such testimony can never meet the "helpfulness" standard of Fed.R.Evid. 702. We hold that the district court erred. We also hold that the admission of such expert testimony is not automatic but conditional. First, the evidence must survive preliminary scrutiny in the course of an in limine proceeding conducted by the district judge. This threshold inquiry, which we derive from the helpfulness standard of Rule 702, is essentially a balancing test, centering on two factors: (1) the reliability of the scientific principles upon which the expert testimony rests, hence the potential of the testimony to aid the jury in reaching an accurate resolution of a disputed issue; and (2) the likelihood that introduction of the testimony may in some way overwhelm or mislead the jury. Second, admission depends upon the "fit," i.e., upon a specific proffer showing that scientific research has established that particular features of the eyewitness identifications involved may have impaired the accuracy of those identifications. The district court's assessment of these factors will guide its discretion in deciding whether to admit the evidence under Fed.R.Evid. 702, which contemplates a liberal view toward the admissibility of expert testimony generally. The district court's ruling under Fed.R.Evid. 702 will be reviewable under an abuse of discretion standard. Finally, the district court retains discretionary authority under Fed.R.Evid. 403 to exclude any relevant evidence that would unduly waste time or confuse the issues at trial.
The defendant in this case was convicted solely on the basis of eyewitness testimony. On the record before us the error cannot be deemed harmless, and accordingly we will vacate the judgment of conviction. It is possible that the district court might conclude, after holding a foundation hearing required by Fed.R.Evid. 702 in this case, that the proffered expert testimony is inadmissible in which case a new trial would be unnecessary. We therefore remand for such a hearing on admissibility, cf. Waller v. Georgia, ___ U.S. ___, 104 S.Ct. 2210, 2217, 81 L.Ed.2d 31 (1984);
Appellant, John W. Downing, was indicted for mail fraud, 18 U.S.C. §§ 1341 & 1342; wire fraud, 18 U.S.C. § 1343; and interstate transportation of stolen property, 18 U.S.C. § 2314. All counts of the indictment arose from a scheme to defraud numerous vendors conducted in 1978 and 1979 by a group of individuals calling themselves the Universal League of Clergy (U.L.C.). U.L.C. operated first out of Bedford, Massachusetts, and then out of Blue Bell, Pennsylvania. Its modus operandi was essentially as follows. U.L.C. representatives at national trade shows made contact with manufacturers' representatives by expressing an interest in their product line. When the representative took an order for his product, U.L.C. furnished the vendor with the list of supposed credit references. In fact, U.L.C. had compiled a list of non-existent trade and bank references; the trade addresses were actually the addresses of mail-drops, and the bank reference was a foreign post office box. Later, when the credit department of the manufacturer investigated the "references" — usually by mail — it received favorable reports concerning U.L.C.'s payment history with other corporate creditors and assurances from the "bank" that U.L.C.'s account was substantial. These reports, the government established, were actually supplied by U.L.C. itself after collecting the credit inquiries from the various mail-drops. These positive credit references usually induced the manufacturer to ship goods to U.L.C. on credit. U.L.C. then disposed of the goods, without making payment to the manufacturers.
U.L.C. was represented in these dealings by men identifying themselves as U.L.C. clergy, including "Reverend" or "`Doctor' Claymore," "Malcolm Sloane," "Reverend Olson," "Paul Eaton," and "Richard Thomas." The government contended that the individuals acting as the U.L.C. clergy were actually appellant and his co-defendants, James A. Silva and Richard Piazza. The central issue at the trial was the identification of appellant as Reverend Claymore. Silva and Piazza admitted setting up U.L.C., but denied knowing that the suppliers were going to be defrauded. They asserted that they were innocent dupes of Reverend Claymore, who masterminded the entire scheme. They (along with appellant) further asserted that appellant was not Claymore, and that if the government could only find the real Claymore, their innocence would be proved.
The government's case against appellant consisted primarily of the testimony of twelve eyewitnesses who, with varying degrees of confidence, testified that appellant was the man they knew as Reverend Claymore.
In an effort to overcome the substantial weight of twelve eyewitness identifications in the jury's mind, appellant's counsel, at the beginning of the trial, inquired whether the court would permit expert testimony on the unreliability of eyewitness testimony. Transcript Vol. 43, at 4-2 to 4-5. The district court deferred ruling on the motion and requested that appellant's counsel inform it during a break in the proceedings as to the substance of the proposed expert testimony, and as to any federal cases that have held such testimony to be admissible. On the tenth day of trial, following an off-the-record side-bar discussion, the court briefly summarized the parties' positions and then denied appellant's motion:
Transcript, Vol. 55, at 3-4.
This dialogue represents the total on-the-record discussion concerning the admissibility of defendant's expert testimony. The case went to the jury without the expert's testimony and appellant was convicted. He appeals, asserting that the district court's exclusion of his expert's testimony was erroneous and harmful within the meaning of Fed.R.Evid. 103(a).
As the transcript of the colloquy indicates, the district court articulated two reasons for refusing to permit appellant's expert witness to testify: (1) the witness would usurp the "function of the jury"; and (2) there was additional evidence "such as fingerprints [and] handwriting." We note at the outset, and the government concedes, that the court was in error as to the second ground: no fingerprint or handwriting evidence was offered against appellant; rather, the government's case rested
The first ground for the court's decision does not proceed from a similar misapprehension of the record, but the court's reasoning in this regard does lack clarity. Initially, it would appear that the court was concerned that the expert witness would testify as to the "ultimate issue of fact," Fed.R.Evid. 704. Were this so, the first ground of decision would also be erroneous. As the advisory committee's note on Rule 704 points out, the basic approach to opinion testimony in the federal rules is one of helpfulness. "In order to render this approach fully effective and to allay any doubt on the subject, the so-called `ultimate issue' rule is specifically abolished by [Rule 704]." Notes of Advisory Committee on Proposed Rule 704.
In light of this clear mandate of Fed.R.Evid. 704, it appears rather that the district court based its ruling on an interpretation of Fed.R.Evid. 702, in effect concluding that expert testimony concerning the reliability of eyewitness identifications is never admissible in federal court because such testimony concerns a matter of common experience that the jury is itself presumed to possess. Under this approach, an expert's testimony on the reliability of eyewitnesses can never meet the test for the admissibility of expert testimony contained in Fed.R.Evid. 702.
This rule invests trial courts with broad discretion to admit expert testimony over the objection that it would improperly invade the province of the jury. Under Rule 702, "an expert can be employed if his testimony will be helpful to the trier of fact in understanding evidence that is simply difficult, [though] not beyond ordinary understanding." S. Saltzburg & K. Redden, Federal Rules of Evidence Manual 451 (3d ed. 1982). See also Notes of Advisory Committee on Proposed Rule 702 (quoting Ladd, Expert Testimony, 5 Vand.L. Rev. 414, 418 (1952)); 3 J. Weinstein & M. Berger, Weinstein's Evidence § 702, at 702-12 n. 6 (citing cases). Cf. Breidor v. Sears, Roebuck and Co., 722 F.2d 1134, 1138 (3d Cir.1983) (citing Salem v. United States Lines Co., 370 U.S. 31, 35, 82 S.Ct. 1119, 1122, 8 L.Ed.2d 313 (1962)) (district court has broad discretion to admit or exclude expert evidence, and its action will be sustained unless manifestly erroneous); Knight v. Otis Elevator Company, 596 F.2d 84, 87 (3d Cir.1979) (noting the liberal policy of admitting expert testimony which will "probably aid" the trier of fact).
Notwithstanding the fact that the Rule 702 standard usually favors admissibility, see In re Japanese Electronic Products Antitrust Litigation, 723 F.2d 238, 279 (3d Cir.1983), several courts of appeals have upheld the exclusion of expert testimony on eyewitness perception and memory because the testimony would involve questions that "can be adequately addressed in cross examination and that the jury can adequately weigh ... through common-sense evaluation." United States v. Thevis, 665 F.2d 616, 641 (5th Cir.1982). See also United States v. Fosher, 590 F.2d 381, 383 (1st Cir.1979) (offer of testimony focusing on general problems of eyewitness identification
We have serious doubts about whether the conclusion reached by these courts is consistent with the liberal standard of admissibility mandated by Rule 702.
The proffer stated that the expert would testify concerning: (1) the "forgetting curve," i.e., the fact that memory does not diminish at a uniform rate; (2) the fact that, contrary to common understanding, stress causes inaccuracy of perception and distorts one's subsequent recall; (3) the "assimilation factor," which indicates that witnesses frequently incorporate into their identifications inaccurate information gathered after the event and confused with the event; (4) the "feedback factor," which indicates that where identification witnesses discuss the case with each other they can unconsciously reinforce their individual identifications; and (5) the fact that studies demonstrate the absence of a relationship between the confidence a witness has in his or her identification and the actual accuracy of that identification.
In another case, United States v. Smith, 736 F.2d 1103 (6th Cir.1984) (per curiam), the Sixth Circuit held that expert testimony on the reliability of eyewitness identification met the "helpfulness" test of Rule 702 and therefore had been improperly excluded.
The California Supreme Court has recently adopted this view. In People v. McDonald, 37 Cal.3d 351, 208 Cal.Rptr. 236, 690 P.2d 709 (1984) (summarized in 36 Crim.L.Rep. (BNA) 2201 (Dec. 19, 1984)), the Court held that, under certain narrow circumstances, it will be error for trial courts to exclude qualified expert testimony on eyewitness perception and memory.
We agree with the courts in Chapple, Smith, and McDonald that under certain circumstances expert testimony on the reliability of eyewitness identifications can assist the jury in reaching a correct decision and therefore may meet the helpfulness requirement of Rule 702. For example, most people, and hence most jury members,
Judicial resistance to the introduction of this kind of expert testimony is understandable given its innovativeness and the fear of trial delay spawned by the spectre of the creation of a cottage industry of forensic psychologists.
The conclusion that expert testimony on the perception of eyewitnesses, at least in certain cases, meets the helpfulness standard of Rule 702 does not end our analysis. On remand, the district court will still have to decide whether to admit the specific testimony proffered in this case. This exercise of the district court's discretion will be shaped by the policies of Fed.R.Evid. 702, as it impinges on the court's assessment of the scientific basis for the profferred testimony, and by the policies of Fed.R.Evid. 403. The balance of this section is devoted to a discussion of the perceived evidentiary problems posed by novel forms of scientific expertise, generally, and to an analysis of the test announced in Frye v. United States, 293 Fed. 1013 (D.C.Cir.1923), as a way of dealing with those problems. We conclude that the status of the Frye test under Rule 702 is somewhat uncertain, but reject that test for reasons of policy. In section IV, we set forth an alternative standard for evaluating novel scientific evidence that we believe comports with the language and policy of Rule 702. Section V addresses the impact of Fed.R.Evid. 403 on the district court's task on remand.
Courts and commentators have divided over the issue of the foundational requirements for the admission of scientific testimony. Evidence that derives from principles and techniques of uncontroverted validity is, of course, readily admissible, subject to the qualification of the proposed witness and, in some jurisdictions, to a showing that proper safeguards were employed in obtaining the evidence on the relevant occasion.
Other courts and commentators have suggested variations on the Frye standard, see, e.g., S. Saltzburg & K. Redden, Federal Rules of Evidence Manual 452 (3d ed. 1982) ("reasonable scientific acceptance"), or alternative approaches. See, e.g., State v. Temple, 302 N.C. 1, 273 S.E.2d 273 (1981) (new scientific evidence can be admitted when its accuracy and reliability have become established and recognized); Giannelli, "The Admissibility of Novel Scientific Evidence: Frye v. United States, A Half Century Later," 80 Colum.L.Rev. 1197, 1249-50 (1980) (criminal defendant and civil litigants should be required to establish the validity of the scientific principle or technique by a preponderance of the evidence; the prosecution in a criminal trial should be required to prove validity beyond a reasonable doubt).
Finally, a third group of courts and commentators reasons that the novelty of the scientific basis for expert testimony bears principally on the weight of the evidence, and that the Federal Rules of Evidence suggest, if not mandate, a generalized "relevancy" approach akin to the balancing test codified in Fed.R.Evid. 403. See United States v. Williams, 583 F.2d 1194, 1198 (2d Cir.1978) (court relies on the "established considerations applicable to the admissibility of evidence"), cert. denied, 439 U.S. 1117, 99 S.Ct. 1025, 59 L.Ed.2d 77 (1979); State v. Hall, 297 N.W.2d 80 (Iowa 1980) (en banc); 3 J. Weinstein & M. Berger, Weinstein's Evidence, ¶ 702, at 702-15 to -21.
As is apparent, a considerable amount of judicial and scholarly attention has been devoted to identifying when evidence resting on novel scientific principles or techniques is admissible. Because this court has never adopted a a clear position on this issue, we must decide, based on the language and policies of the Federal Rules of Evidence, the appropriate test for the admissibility of novel scientific evidence.
Our starting point for this discussion is the seminal opinion of Frye v. United States, 293 Fed. 1013 (D.C.Cir.1923), which had won adherents in many state and federal courts at the time of the adoption of the Federal Rules of Evidence. See Giannelli, supra, at 1228-29. The Frye court
Frye, 293 F. at 1014 (emphasis added). Under Frye, therefore, courts confronted with a proffer of novel scientific evidence must make a preliminary determination through the introduction of other evidence, including expert testimony, regarding (1) the status, in the appropriate scientific community, of the scientific principle underlying the proffered novel evidence; (2) the technique applying the scientific principle; and (3) the application of the technique on the particular occasion or occasions relevant to the proffered testimony. See Giannelli, supra, at 1201. See, e.g., United States v. Brown, 557 F.2d 541, 557 (6th Cir.1977) (applying Frye test to ion microprobic analysis); United States v. Tranowski, 659 F.2d 750, 754-57 (7th Cir.1981) (applying Frye test to testimony by astronomer purporting to date a photograph by measuring lengths of shadows on the photo). Once a novel form of expertise is judicially recognized, this foundational requirement can be eliminated, as is done when, for example, fingerprint, ballistics, or x-ray evidence is offered. See generally Giannelli, supra, at 1248; cf. 1 D. Louisell & C. Mueller, Federal Evidence § 105, 826-27 (1977) (general acceptance standard should be absorbed in judicial notice concept which allows courts to admit scientific evidence without testimony describing the principles resolved); McCormick on Evidence, supra, at 608.
Because the general acceptance standard set out in Frye was the dominant view within the federal courts at the time the Federal Rules of Evidence were considered and adopted, one might expect that the rules themselves would make some pronouncement about the continuing vitality of the standard. Neither the text of the Federal Rules of Evidence nor the accompanying notes of the advisory committee, however, explicitly set forth the appropriate standard by which the admissibility of novel scientific evidence is to be established. Although the commentators agree that this legislative silence is significant, they disagree about its meaning. Professors Saltzburg and Redden, for example, have stated, "[i]t would be odd if the Advisory Committee and the Congress intended to overrule the vast majority of cases excluding such evidence as lie detectors without explicitly stating so." Saltzburg & Redden, supra, at 452. See also 1 D. Louisell & C. Mueller, supra, § 105, at 818 ("Probably the general scientific acceptance approach has survived the enactment of the Federal Rules, and will continue to be applied in determining the relevancy of such proof under Rule 401."); Giannelli, supra, at 1228-29.
The opposing view, espoused by Judge Weinstein, Professor Berger, and others, maintains that "[T]he silence of the rule  and its drafters should be regarded as tantamount to an abandonment of the general acceptance standard." J. Weinstein & M. Berger, supra, ¶ 702 at 702-16. See also C. Wright & K. Graham, 22 Federal Practice and Procedure § 5168, at 86-90 (1978). Cf. State v. Williams, 388 A.2d 500, 503 (Me.1978) (interpreting Maine rules of evidence, which are patterned after the federal rules, as not incorporating Frye). Arguing that Frye is inconsistent with the policies animating the Federal Rules of Evidence, this view focuses in particular on the broad scope of relevance in the federal rules. Fed.R.Evid. 401 specifically defines relevant evidence as "evidence having 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." Moreover, Fed.R.Evid. 402 provides that "[a]ll relevant evidence is admissible, except as otherwise provided by the Constitution of the United States, by Act of Congress, by these rules,
Although we believe that "helpfulness" necessarily implies a quantum of reliability beyond that required to meet a standard of bare logical relevance, see discussion infra, it also seems clear to us that some scientific evidence can assist the trier of fact in reaching an accurate determination of facts in issue even though the principles underlying the evidence have not become "generally accepted" in the field to which they belong. Moreover, we can assume that the drafters of the Federal Rules of Evidence were aware that the Frye test was a judicial creation, and we find nothing in the language of the rules to suggest a disapproval of such interstitial judicial rulemaking. Therefore, although the codification of the rules of evidence may counsel in favor of a re-examination of the general acceptance standard, on balance we conclude that the Federal Rules of Evidence neither incorporate nor repudiate it. Cf. Saltzburg & Redden, supra, at 452 (suggesting the decision as to the proper standard for evaluating scientific evidence will continue to be made on a case-by-case basis). We will consider, therefore, the advantages of and the problems associated with Frye's general acceptance standard.
The most important justification for the Frye test is that it provides a method by which courts can assess the reliability of novel scientific expert testimony. See United States v. Addison, 498 F.2d 741, 743-44 (D.C.Cir.1974). The general acceptance standard in effect permits the experts who know most about a procedure to form a "technical jury," whose positive assessment of the scientific status of a procedure becomes a necessary prerequisite to the admissibility of expert testimony based on the procedure. See People v. Barbara, 400 Mich. 352, 405, 255 N.W.2d 171, 194 (1977). Adherents of the general acceptance standard also argue that it guarantees the existence of a coterie of experts qualified to testify about the status of a particular scientific technique and, in theory at least, promotes uniformity of decision. United States v. Addison, 498 F.2d at 744; Reed v. State, 283 Md. 374, 388, 391 A.2d 364, 371-72 (1978).
The general acceptance standard also safeguards against the possible prejudicial effects of testimony based upon "an unproved hypothesis in an isolated experiment." United States v. Brown, 557 F.2d 541, 556 (6th Cir.1977). The concern over potentially specious expert testimony assumes particular importance in the criminal context, where the general acceptance standard has had its most substantial impact.
Notwithstanding the valid evidentiary concerns subsumed in the general acceptance standard, critics of the standard have cited two general problems with it: its vagueness and its conservatism. See, e.g., 1 D. Louisell & C. Mueller, supra, § 105, at 821. Professor Giannelli's excellent and comprehensive article catalogues the numerous difficulties that have arisen in applying the test. Giannelli, supra, at 1208-28. First, the vague terms included in the standard have allowed courts to manipulate the parameters of the relevant "scientific community" and the level of agreement needed for "general acceptance." Thus, some courts, when they wish to admit evidence, are able to limit the impact of Frye by narrowing the relevant scientific community to those experts who customarily employ the technique at issue. See, e.g., People v. Williams, 164 Cal.App.2d Supp. 858, 331 P.2d 251 (App. Dep't Super.Ct. 1958) (in admitting results of the Nalline test for narcotics use, the court held that the Frye test was satisfied upon showing of general acceptance by those who are expected to be familiar with the use of the technique, although the prosecution's own expert had conceded the lack of acceptance within the medical profession generally).
Professor Giannelli and others have discussed other problems that arise in applying the Frye test: the selectivity among courts in determining whether evidence derives from "novel" principles; the inadequacy of expert testimony on many scientific issues; an uncritical acceptance of prior judicial, rather than scientific, opinion as a basis for finding "general acceptance"; and the narrow scope of review by which some appellate courts review trial court rulings. See Giannelli, supra, at 1208-21. All of these problems contribute to the "essential vagueness" of the Frye test. 1 D. Louisell & C. Mueller, supra, at 821.
Apart from these various difficulties in implementation, moreover, Frye's general acceptance standard has been found to be unsatisfactory in other respects. Under Frye, some have argued, courts may be required to exclude much probative and reliable information from the jury's consideration, thereby unnecessarily impeding the truth-seeking function of litigation.
In sum, the Frye test suffers from serious flaws. The test has proved to be too malleable to provide the method for orderly and uniform decision-making envisioned by some of its proponents. Moreover, in its pristine form the general acceptance standard reflects a conservative approach to the admissibility of scientific evidence that is at odds with the spirit, if not the precise language, of the Federal Rules of Evidence. For these reasons, we conclude that "general acceptance in the particular field to which [a scientific technique] belongs," Frye, 293 F. at 1014, should be rejected as an independent controlling standard of admissibility. Accordingly, we hold that a particular degree of acceptance of a scientific technique within the scientific community is neither a necessary nor a sufficient condition for admissibility; it is, however, one factor that a district court normally should consider in deciding whether to admit evidence based upon the technique.
The language of Fed.R.Evid. 702, the spirit of the Federal Rules of Evidence in general, and the experience with the Frye test suggest the appropriateness of a more flexible approach to the admissibility of novel scientific evidence. In our view, Rule 702 requires that a district court ruling upon the admission of (novel) scientific evidence, i.e., evidence whose scientific fundaments are not suitable candidates for judicial notice, conduct a preliminary inquiry focusing on (1) the soundness and reliability of the process or technique used in generating the evidence, (2) the possibility that admitting the evidence would overwhelm, confuse, or mislead the jury, and (3) the proffered connection between the scientific research or test result to be presented, and particular disputed factual issues in the case.
In establishing the reliability of novel scientific evidence as one criterion of its admissibility under Rule 702, we join a growing number of courts that have focused on reliability as a critical element of admissibility. See, e.g., State v. Temple, 302 N.C. 1, 273 S.E.2d 273, 280 (1981) (evidence based on new scientific methods will be admitted when the demonstrated accuracy and reliability of the method have become established and recognized); State v. Kersting, 50 Or.App. 461, 623 P.2d 1095, 1101 (1981) (evidence based on a scientific technique that is not generally accepted may be admitted if there is "credible evidence on which the trial judge may make the initial determination that the technique is reasonably reliable"), aff'd, 292 Or. 350, 638 P.2d 1145 (1982); cf. D'Arc v. D'Arc, 157 N.J.Super. 553, 385 A.2d 278 (1978) (recognizing a distinction between the general acceptance standard and a standard based upon reliability, and upholding the admissibility of evidence that satisfies either test).
The reliability inquiry that we envision is flexible and may turn on a number of considerations, in contrast to the process of scientific "nose-counting" that would appear to be compelled by a careful reading of Frye. Unlike the Frye standard, the 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. The district court in assessing reliability may examine a variety of factors in addition to scientific acceptance. In many cases, however, the acceptance factor may well be decisive, or nearly so. Thus, we expect that a technique that satisfies the Frye test usually will be found to be reliable as well. On the other hand, a known technique which has been able to attract only minimal support within the community is likely to be found unreliable. See United States v. Williams, 583 F.2d 1194, 1198 (2d Cir.1978), cert. denied, 439 U.S. 1117, 99 S.Ct. 1025, 59 L.Ed.2d 77 (1979).
Where a form of scientific expertise has no established "track record" in litigation, the court may look to other factors that may bear on the reliability of the evidence.
The frequency with which a technique leads to erroneous results will be another important component of reliability. At one extreme, a technique that yields correct results less often than it yields erroneous one is so unreliable that it is bound to be unhelpful to a finder of fact. Conversely, a very low rate of error strongly indicates a high degree of reliability. In addition to the rate of error, the court might examine the type of error generated by a technique.
After assessing the reliability of the evidence, the court must also weigh any danger that the evidence might confuse or mislead the jury. It may seem paradoxical to suggest that scientific evidence based on principles bearing substantial indicia of reliability could confuse rather than assist the jury, but we do not doubt that this may be so, in some cases. One example might involve a technique which has "assume[d] a posture of mythic infallibility," Addison v. United States, 498 F.2d 741, 744 (D.C.Cir.1974), among lay persons, or at least one whose shortcomings are, for some reason, unlikely to be effectively communicated to the jury. The degree to which an unwarranted "aura of reliability," United States v. Baller, 519 F.2d 463, 466 (4th Cir.), cert. denied, 423 U.S. 1019, 96 S.Ct. 456, 46 L.Ed.2d 391 (1975), attaches to scientific evidence will naturally vary with the type of evidence. The danger that scientific evidence will mislead the jury might be greater, for example, where the jury is not presented with the data on which the expert relies, but must instead accept the expert's assertions as to the accuracy of his conclusions. Cf. People v. Marx, 54 Cal.App.3d 100, 111, 126 Cal.Rptr. 350, 356 (1975) (in support of its holding admitting bite mark comparison evidence, the court noted that "the basic data on which the experts based their conclusions were verifiable by the court"), cited in 3 J. Weinstein & M. Berger, supra, ¶ 702 at 702-20 n. 18. Techniques that rely on the use of a mechanical device to produce data as well as upon the exercise of an expert's subjective judgment to draw conclusions from the data would also seem to raise at least the possibility of confusing or misleading the jury.
With respect to the procedure that district courts should follow in making preliminary determinations regarding admissibility of evidence, we recognize that "`the control of the order of proof at trial is a matter committed to the discretion of the trial judge.'" United States v. Ammar, 714 F.2d 238, 246 (3d Cir.1983) (quoting United States v. Continental Group, Inc., 603 F.2d 444, 456 (3d Cir.1979), cert. denied, 444 U.S. 1032, 100 S.Ct. 703, 62 L.Ed.2d 668 (1980)), cert. denied sub nom. Stillman v. United States, ___ U.S. ___, 104 S.Ct. 344, 78 L.Ed.2d 311 (1983). Hence, we will not prescribe any mandatory procedures that district courts must follow in every case involving proffers of scientific evidence. A few general observations in this regard are appropriate, however.
It would appear that the most efficient procedure that the district court can use in making the reliability determination is an in limine hearing. Such a hearing need not unduly burden the trial courts; in many cases, it will be only a brief foundational hearing either before trial or at trial but out of the hearing of the jury. In the course of the in limine proceeding, the trial court may consider, inter alia, offers of proof, affidavits, stipulations, or learned treatises, see Fed.R.Evid. 803(18), in addition to testimonial or other documentary evidence (and, of course, legal argument). In addition, the court may properly consider the testimony presented to other courts that have addressed the same evidentiary issue, and the opinions of those courts on the subject. If a technique has found favor with a significant number of other courts, a district court may exercise its discretion to admit the evidence through judicial notice.
Having generally set out the appropriate inquiry, we now turn to the facts of this case. Unfortunately the district court never addressed the reliability question because it essentially — and erroneously — concluded that expert evidence of this type could never assist the trier of fact. From the facts available on the record and otherwise, it would appear that the scientific basis for the expert evidence in question is sufficiently reliable to satisfy Rule 702. In a recent case approving the use of expert testimony on eyewitness perception and
An additional consideration under Rule 702 — and another aspect of relevancy — is whether expert testimony proffered in the case is sufficiently tied to the facts of the case that it will aid the jury in resolving a factual dispute. In this regard, we hold that a defendant who seeks the admission of expert testimony must make an on-the-record detailed proffer to the court, including an explanation of precisely how the expert's testimony is relevant to the eyewitness identifications under consideration. The offer of proof should establish the presence of factors (e.g., stress, or differences in race or age as between the eyewitness and the defendant) which have been found by researchers to impair the accuracy of eyewitness identifications. See People v. McDonald, supra, 37 Cal.3d 351, 208 Cal.Rptr. at 253, 690 P.2d at 726. See discussion of Chapple, supra text preceding note 7, in which the proffered evidence was found to be sufficiently tied to the case. Failure to make such a detailed proffer is sufficient grounds to exclude the expert's testimony. See United States v. Fosher, 590 F.2d 381, 383 (1st Cir.1979).
Turning to the facts of the present case, we note that appellant made no such on-the-record proffer, but conclude that this defect is not fatal on this appeal for two reasons. First, the district court did not rely on this failure to justify its decision to exclude appellant's expert. Second, the district court conducted all proceedings concerning the admissibility of appellant's expert's testimony off the record. With the resulting undeveloped record, we simply have no way of judging whether the proffered testimony was sufficiently tied to the facts of the case. The encounters between the identification witnesses and appellant were apparently not under conditions of stress, nor so far as we know, was there a potential cross-racial identification problem. It is conceivable, however, that the off-the-record expert proffer made by the appellant was sufficiently tied to the facts of the case to satisfy Rule 702. Therefore we cannot affirm the district court's exclusion of the expert evidence on this ground, and the district court will have to explore this question of "fit" on remand.
The Rule 702 analysis we have outlined incorporates to some extent a consideration of the dangers, particularly the danger of unfair prejudice, enumerated in Fed.R.Evid. 403. On remand, however, even if the proffered evidence satisfies Rule 702, the district court may decide nonetheless to
The availability of other methods that would serve the purposes for which the appellant seeks to introduce expert testimony may also serve to justify exclusion under Rule 403, though we do not perceive the viability of such an alternative in this case. Moreover, as an abstract proposition, it would seem anomalous to hold that the probative value of expert opinion offered to show the unreliability of eyewitness testimony so wastes time or confuses the issue that it cannot be considered even when its putative effect is to vitiate the only (eyewitness) evidence offered by the government.
For the reasons set forth above, we must vacate the judgment of conviction entered against the appellant. As we have explained, because the crucial evidence against appellant consisted solely of eyewitness identification, we cannot conclude on this record that the district court's error in excluding the proffered expert testimony is harmless. See supra note 26. Appellant was deprived at most, however, of the opportunity to present his expert witness. The district court's error will become harmless if on remand the district court, in the exercise of its Rule 702 or 403 discretion, decides that the proffered testimony is not admissible. Therefore, we conclude that a new trial is required only if the district court determines that the proffered testimony is admissible. Cf. Waller v. Georgia, ___ U.S. ___, 104 S.Ct. 2210, 2217, 81 L.Ed.2d 31 (1984) ("If, after a new suppression hearing, essentially the same evidence is suppressed, a new trial presumably
Therefore, the judgment of conviction will be vacated and the case will be remanded to the district court for an evidentiary hearing concerning the admissibility of appellant's proffered expert testimony. If the court determines that the expert testimony should have been admitted, it is directed to grant a new trial. If the court decides that the testimony is not admissible under Rule 702 (or should be excluded under Rule 403), then the judgment of conviction against appellant should be reinstated.
DUMBAULD, Senior District Judge, concurring.
Rule 403 of the Federal Rules of Evidence provides that "although relevant, evidence may be excluded if its probative value is substantially outweighed ... by considerations of undue delay, waste of time, or needless presentation of cumulative evidence."
In excluding defendant's proffer of an expert witness regarding the unreliability of eyewitness identification testimony (a weakness known at least since Hugo Munsterberg's experiments at Harvard and ordinarily presented adequately to the jury by argument of counsel), the District Judge did not invoke Rule 403 eo numero or place on the record any "extensively articulated ... extensive explication" thereunder.
However, under part V of Judge Becker's opinion (which is truly a minor magnum opus of jurisprudential virtuosity) the District Court upon remand remains free to do so without preclusion by our present decision of its exercise of discretion under Rule 403. I therefore concur in the disposition made of the case.
I agree with the Court's opinion that there can be cases where expert opinion of this type may be useful. But with respect to the case at bar it seems plain to me that any error by the District Judge was harmless. A dozen witnesses, who had spent from 5 to 45 minutes in negotiations with the defendant while he "conned" them with his fraudulent scheme, identified him. This case did not involve a momentary glimpse of a bank robber at the teller's window or a rape perpetrated under a ski mask. It would be unfortunate if his conviction and the time spent at his trial were to go down the drain because of an academic error regarding the intellectual foundations for judicial acceptance of novel scientific disciplines.
McDonald, 37 Cal.3d 351, 208 Cal.Rptr. at 247, 690 P.2d at 727 (footnote omitted).
E. Cleary, McCormick on Evidence 613 (3d ed. 1984) (footnotes omitted). Professor Giannelli also has noted the divergence of views among courts as to whether a showing that a scientific technique was properly applied on a particular occasion goes to the admissibility of scientific evidence or only to its weight. See Giannelli, "The Admissibility of Novel Scientific Evidence: Frye v. United States A Half Century Later," 80 Colum.L.Rev. 1197, 1201-02 & nn. 22-24 (1980).
Professor Imwinkelreid argues that the qualification of a scientific process is embraced within this rule, and that the trial court must therefore leave to the jury the determination of the validity and reliability of the process so long as the proponent of the evidence adduces evidence sufficient to support a finding by a reasonable juror that the process is reliable. Under this view, the validity of the scientific process is treated purely as a matter of conditional relevancy, see Fed.R.Evid. 104(b).
We disagree. The question whether "a particular machine works as intended" is a question distinct from one directed toward "the authentication of a process generally." Saltzburg & Redden, Federal Rules of Evidence Manual 702 (3d ed. 1982). Rule 901(b)(9) speaks only to the former question. See McCormick on Evidence 885 n. 6 (3d ed. 1984) ("The emphasis of Rule 901 is upon showing that the offered item [e.g., a computer printout] is what it is claimed to be, i.e., that it is genuine ... rather than that what is in the [computer] is correct.").
The examples provided by the Advisory Committee in the note accompanying Fed.R.Evid. 901 support this interpretation of the rule as it bears on novel scientific evidence. The note cites x-ray and computer evidence as two "situations in which the accuracy of a result is dependent upon a process or system which produces it." Notes of Advisory Committee on Proposed Rule 901. These two examples are distinguishable from the "novel" techniques that implicate the concerns addressed by the Frye test and our alternative to it. The underlying principles behind x-ray and computers are well understood; as to these technologies, serious questions of accuracy or reliability arise, if at all, only in connection with their application in a particular instance.
In contrast, novel scientific evidence carries with it concerns over trustworthiness and reliability akin to those raised by offers of hearsay evidence. See supra note 16. When there is a serious question of reliability of evidence, it is appropriate for the court to exercise to some degree an evidentiary screening function, United States v. Ammar, 714 F.2d 238, 268 (3d Cir.1983) (Becker, J., concurring) (discussing judge's role in making a preliminary determination that the conditions specified in Fed.R.Evid. 801(d)(2)(e) are satisfied), cert. denied sub nom. Stillman v. United States, ___ U.S. ___, 104 S.Ct. 344, 78 L.Ed.2d 311 (1983).
The major thrust of Professor Imwinkelreid's article is that, because of the potential dangers raised by novel scientific evidence, prudence counsels that the court play a role in keeping unreliable scientific evidence from the jury. Imwinkelreid, supra, at 581. To that end, Professor Imwinkelreid supports an amendment to Fed.R.Evid. 901 that would expressly permit the court to play such a role. Id. at 616. We share his view on the need for certain safeguards against unreliable scientific evidence, but dispute the proposition that an amendment to the evidence rules is required to implement them.