If the Shoe Fits

The Third Circuit has published an opinion upholding the trial court's decision to admit shoeprint identification testimony in a bank robbery case. See United States v. Ford, No. 05-4998 (3d Cir. Mar. 29, 2007) (Smith, Fisher, & Dowd, JJ.).

The news that forensic testimony has withstood Daubert scrutiny in a criminal case falls decidedly in the dog-bites-man category. But the Ford opinion also contains a pair of interesting footnotes on two topics of more general interest: (1) the vexing problem of "fit"; and (2) the level of confidence or certainty with which an expert may (or must) express (or hold) his or her views -- an issue that has figured prominently in opinions handed down during the past week or so (see our posts of 3/21/07, 3/27/07, and 3/28/07 ).

(1) "Fit"

Ever since Justice Blackmun's passing and somewhat cryptic reference to "fit" in the Daubert opinion, judges and lawyers alike have struggled to assign some determinate meaning to the concept. Is it simply a more demanding version of the relevance standard, or does it have some narrower and perhaps more technical meaning? The latter, narrower interpretation is suggested by review of the case from which Justice Blackmun borrowed the "fit" terminology -- a Third Circuit decision involving expert testimony on the accuracy of eyewitness identification, in which the court established a requirement for detailed evidentiary proffers showing that the research invoked by the expert spoke to the specific kinds of impediment to accurate identification allegedly presented by the factual circumstances of the case. See United States v. Downing, 753 F. 2d 1224, 1242 (3d Cir. 1985). The broader, "heightened relevance" interpretation, however, has also been espoused -- most notably by Judge Kozinski, in the Ninth Circuit's opinion on remand from the Supreme Court's decision in Daubert.

Yesterday's opinion in Ford comments on the issue as follows, in footnote 6:

The discussion of "fit" in [In re Paoli R.R. Yard PCB Litigation, 35 F.3d 717 (3d Cir. 1994)] indicated that the standard for analyzing the fit of an expert's analysis to the case at hand is "not that high," but is "higher than bare relevance." Id. at 745. That statement remains sound law inasmuch as it requires that experts who purport to apply their principles and methods to the facts of the case do so in a reliable manner. The Paoli Court's discussion of fit requires that expert opinions that apply principles or methods to the facts of the case and produce conclusions that have a debatable connection to the question in issue be predicated on a reliable methodology. Id. This is the critical import of Paoli's discussion of fit within the context of reliability. Outside of this relatively narrow setting, "fit" is a relevance concern.

Following Paoli, this Court reiterated the helpfulness discussion in Daubert, and noted the Supreme Court's explanation that "[f]it is not always obvious, and scientific validity for one purpose is not necessarily validity for other unrelated purposes." In re TMI Litigation, 193 F.3d 613, 670 (3d Cir. 1999) (quoting Daubert, 509 U.S. at 591). We emphasized again that "[t]his requirement [of 'fit'] is one of relevance and expert evidence which does not relate to an issue in the case is not helpful." Id.

In its reconsideration of Daubert on remand, the Ninth Circuit explained that

[t]he Supreme Court recognized that the "fit" requirement "goes primarily to relevance," but it obviously did not intend the second prong of Rule 702 to be merely a reiteration of the general relevancy requirement of Rule 402. In elucidating the "fit" requirement, the Supreme Court noted that scientific expert testimony carries special dangers to the fact-finding process because it "'can be both powerful and quite misleading because of the difficulty in evaluating it.'" Federal judges must therefore exclude proffered scientific evidence under Rules 702 and 403 unless they are convinced that it speaks clearly and directly to an issue in dispute in the case, and that it will not mislead the jury.

Daubert v. Merrell Dow Pharm., Inc., 43 F.3d 1311, 1321 n.17 (9th Cir. 1995) (citations omitted) (emphasis added). Although we do not adopt the apparent presumption of exclusion enunciated by the Ninth Circuit, we agree with the spirit of our sister court's exhortation. In particular, district courts should tread carefully when evaluating proffered expert testimony, paying special attention to the relevance prong of Daubert.

The question of fit here is not debatable, as it was in Paoli. See Paoli, 35 F.3d at 779-81 (evaluating the fit between expert testimony on animal studies and the question of human exposure). Thus, we examine the question of whether [the shoeprint expert's] conclusions fit the factual question in issue in the context of our relevance considerations.

The language of footnote 6 is abstract, but if we read it correctly, it adopts something like the Dowd opinion's limited conception of "fit." It appears to say that insofar as "fit" imposes any requirement going beyond ordinary relevance, it comes into play in a special class of cases involving a problematic connectedness between the expert's "principles or methods" and the facts of the case. For example, if the underlying research validated shoeprint identification techniques only for penny loafers, problems of "fit" would arise if the expert applied the techniques to Nikes. In that situation, the "fit" requirement would not necessarily bar the testimony, as we read footnote 6, but it would demand some level of attention to the question whether penny-loafer techniques can reliably be extended to the running-shoe context.

2. Confidence

The expert in Ford did not testify to a definitive match, but only to a similarity between the shoeprints and the soles of the defendant's shoes. The Third Circuit rejected the argument that the testimony should therefore be excluded because it established only the possibility of a match. "An expert opinion that expresses a possibility that a crime scene impression may have been made by shoes worn by the defendant, and otherwise comports with the Daubert analysis," said the court, "is clearly relevant to the question of whether the defendant was present at the scene of the crime." The panel elaborated on that statement in footnote 7 of the Ford opinion:

Indeed, due to the inherently closed factual universe created by the Federal Rules of Evidence and the partisan decisions of litigants in selecting experts, it is desirable to have expert witnesses express their degree of confidence accurately. See Samuel R. Gross and Jennifer L. Mnookin, Expert Information and Expert Evidence: A Preliminary Taxonomy, 34 Seton Hall L. Rev. 141, 143-44 (2003) ("[T]he degree of certainty expressed by the witness should reflect both knowledge and its limits, both what is known and what is not."); id. at 170-71 ("Normally, a witness's level of confidence is grist for the adversarial mill...."); id. at 186. By confining the jury's considerations to the facts and opinions presented to them at trial, the rules circumscribe the amount of available information. Consequently, especially where expert testimony is concerned, the Rules may create an artificially polarized world, leaving the jury to evaluate the often contradictory testimony of dueling experts. Because the parties are apt to select experts based on their ability to provide highly favorable testimony, it is preferable that, where there is cause for doubt as to a particular opinion, the experts make clear any uncertainty.