Friday, February 26, 2016

Is "Reasonable Scientific Certainty" Unreasonable?

Next month, the National Commission on Forensic Science is expected to vote on a proposal to make three recommendations about the testimonial use of phrases such as "to a reasonable degree of scientific certainty" and "to a reasonable degree of [discipline] certainty":
Recommendation #1: The Attorney General should direct all attorneys appearing on behalf of the Department of Justice (a) to forego use of these phrases when presenting forensic discipline testimony unless directly required by judicial authority as a condition of admissibility for the witness’ opinion or conclusion, and (b) to assert the legal position that such terminology is not required and is indeed misleading.

Recommendation #2: The Attorney General should direct all forensic science service providers and forensic science medical providers employed by Department of Justice not to use such language in reports or couch their testimony in such terms unless directed to do so by judicial authority.

Recommendation #3: The Attorney General should, in collaboration with NIST, direct the OSACs to develop appropriate language that may be used by experts when reporting or testifying about results or findings based on observations of evidence and data derived from evidence.
Most of the public comments have been supportive, 1/ but three days ago, one commissioner submitted a comment arguing that Recommendation #1 would require the Department of Justice to argue for overturning existing law that “seem[s] to require” these phrases in some forensic-science identification fields and that Recommendation #3 asks the Attorney General to take action that exceeds her authority.

[Added 3/1/16: At least, this is what I thought the comment was driving at, but, as explained in a follow-up posting, I was mistaken. Nevertheless, I think the analysis of this point is worth leaving up for general viewing, since it addresses a question that might be raised about the proposal.]

The second point is well taken—the Attorney General has no power to “direct” NIST or the OSAC to act, and NIST supports but does not direct the OSAC structure. However, the notion that any federal district court is legally compelled to condition the admission of expert testimony on an obscure phrase like “reasonable scientific certainty” seems farfetched. Below are excerpts from a comment that I filed with the Commission today explaining my thinking (with minor alterations):

Previous drafts of the final document before the Commission included references to the case law and literature supporting the subcommittee’s view that these recommendations are compatible with the existing law of evidence — that the law does not require experts to use these particular (and problematic) phrases, even though some judges and lawyers expect and even prefer to hear them. 2/ The comments that follow do not try to restate the previous legal analysis or to summarize the legal literature. They respond to the analysis in the Feb. 23 Comment. ...

Nothing in the Comment establishes that, when presented with the relevant legal authority and analysis, any court would find it difficult to accept the position the Department is being asked to take. The cases cited in the Comment do not contradict the proposed position. 3/ Not one of these cases considered whether the testifying expert must testify to “a reasonable degree of [discipline] certainty” as opposed to offering an opinion that the markings on a gun or fingerprint offer strong support for the source conclusion (or some similar less-than-absolutely-certain testimony). In most of them, the defense sought to exclude the source-attribution testimony entirely, on the Daubert ground that science and statistics did not support source attributions to one and only one possible source. The trial judges in these cases agreed that absolute, categorical claims of identity were too extreme. Those assertions are the kind of overclaiming that, Deputy Attorney General Yates announced two days ago, the Department of Justice is seeking to avoid.

As an alternative to scientifically indefensible or overstated claims, the trial judges in the cited cases set an upper bound on the certainty that the expert may express — “reasonable certainty” of one kind or another. Other federal trial judges have set other upper bounds. E.g., United States v. Glynn, 578 F.Supp.2d 567 (S.D.N.Y. 2008) (“the ballistics opinions ... may be stated in terms of ‘more likely than not,’ but nothing more”). No court has dictated one formulaic expression to the exclusion of all other ways to solve the problem of expert and prosecutorial exaggeration. 4/ In every one of the cases cutting back on overclaiming, for the government’s experts to have presented less categorically certain phrasing in these cases would not have violated the pretrial orders, and the government easily could have requested somewhat different phrasing as long as it did not amount to the kind overclaiming that the orders were issued to protect against.

United States v. Cazares, 788 F.3d 956 (9th Cir. 2015), the only appellate case that the Comment perceives as demonstrating that “it is an overstatement to categorically claim that the phrase ‘to a reasonable degree of [discipline] certainty’ ‘is not required’” clearly does not demand the use of this phrase instead of more transparent alternatives. No such alternatives were before the Ninth Circuit. The firearms examiner did not use the phrase “reasonable ballistic certainty,” but instead claimed total  “scientific certainty.” Id. at 988. The Assistant U.S. Attorney did the same. Id. The panel excused this testimony and prosecutorial exaggeration as harmless error. 5/ It cited to the cases noted in the Comment only to show that less-than-absolute testimony of firearms identification had been held to satisfy the requirements of Daubert. In an obvious dictum, the court of appeals referred to “reasonable ballistic certainty” as “the proper expert characterization of toolmark identification”—not to prescribe these words as the only permissible mode of expressing conclusions across the realm of forensic identification, but only to make the point that, given the expert’s acknowledgment of subjectivity in her analysis and her concession that “[t]here is no absolute certainty in science,” id. at 988, “[a]ny error in this case from the ‘scientific certainty’ characterization was harmless.” Id. at 990.

Moreover, the nature of the disagreement with the observation that “use of the [reasonable degree of scientific or discipline-specific certainty] phrase is not required by law and is primarily a relic of custom and practice” is difficult to fathom. The Comment agrees that “the use of this phrase is not required by the Federal Rules of Evidence.” This is every bit as true in the Ninth Circuit as the others judicial circuits. What, then, is the basis of the claim that a court is “perhaps” required to insist that an expert use the phrase? The Constitution can override the rules of evidence, but no one can seriously claim that the Constitution conditions expert scientific testimony on a particular form of words — and a potentially misleading mixture of words at that.

In sum, there are courts that find comfort in phrases like "reasonable scientific certainty," and a few courts have fallen back on variants such as "reasonable ballistic certainty" as a response to arguments that identification methods cannot ensure that an association between an object or person and a trace is 100% certain. But it seems fair to say that "such terminology is not required " -- at least not by any existing rule of law.

  1. E.g., Erin Murphy & Andrea Roth, Public Comment on NCFS Recommendation Re: Reasonable Degree of Scientific Certainty, Feb. 23, 2016,!documentDetail;D=DOJ-LA-2016-0001-0011

  2. These have been moved to a separate "views" document available through a link at The recommended position is supported not only by the opinions of appellate courts across the country, but also the writings of federal judges, the drafters of the Federal Rules of Evidence, and the authors of the three leading legal treatises on scientific evidence.

  3. If they did, that would be a reason for the Department to advance a position to harmonize a conflict among the U.S. courts of appeals.

  4. For example, in one case cited in the Comment, United States v. Monteiro, 470 F. Supp. 2d 351 (D. Mass. 2006), the trial judge actually granted the defendant’s motion to exclude firearms testimony (unless the government supplemented the record with information establishing compliance with professional standards). The court then presented “reasonable degree of ballistic certainty” testimony as an acceptable way for the expert may testify,” but the court’s concern was plainly that “the expert may not testify that there is a match to an exact statistical certainty.” Id. at 375.

    Similarly, in United States v. Ashburn, 88 F. Supp. 3d 239 (E.D.N.Y. 2015), the  court’s concern was testimony “that he is ‘certain’ or ‘100%’ sure of his conclusions that two items match, that a match is to ‘the exclusion of all other firearms in the world,’ or that there is a ‘practical impossibility’ that any other gun could have fired the recovered materials.” Id. at 250. The trial judge settled on “reasonable ballistic certainty” as an acceptable alternative, but not necessarily an exclusive one.

    So too, in United States v. Taylor, 663 F.Supp.2d 1170 (D.N.M. 2009), the district judge wrote that:
    Mr. Nichols will be permitted to give to the jury his expert opinion that there is a match between the .30–.30 caliber rifle recovered from the abandoned house and the bullet believed to have killed Mr. Chunn. However, because of the limitations on the reliability of firearms identification evidence discussed above, Mr. Nichols will not be permitted to testify that his methodology allows him to reach this conclusion as a matter of scientific certainty. Mr. Nichols also will not be allowed to testify that he can conclude that there is a match to the exclusion, either practical or absolute, of all other guns. He may only testify that, in his opinion, the bullet came from the suspect rifle to within a reasonable degree of certainty in the firearms examination field.
    Id. at 1180.

  5. The court of appeals reasoned that “the ‘scientific certainty’ characterization was subject to cross examination which resulted in acknowledgment of subjectivity in the expert's work, [and] the district court properly instructed as to the role of expert testimony and there was substantial evidence otherwise linking the defendants to the . . . murders.” Id. at 990.

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