Proposed Changes to Federal Rule of Evidence 702

The following report appeared in the OSAC newsletter OSAC In Brief, July 2021, at 3-7 with the uninspired title "Proposed Changes to Federal Rule of Evidence 702." It was followed by an update in the June 2022 issue (about to be reproduced on this blog). Both are meant to be boringly factual. More opinionated remarks may appear later.

On April 30, the federal Advisory Committee on Evidence Rules unanimously proposed two changes to the wording of Federal Rule of Evidence 702. The rule, which many states have adopted in one form or another, provides for testimony by expert witnesses. The changes do not alter the meaning of the rule, but they can be seen as a course-correction signal telling courts to be more vigorous in ensuring that “forensic expert testimony is valid, reliable, and not overstated in court.”

The quoted words come from a report of the Advisory Committee. Facilitating such testimony also is part of OSAC’s raison d’être. This article for In Brief therefore describes the proposed amendment, a little bit of its history, the steps required for it to be enacted into law, and its significance for OSAC’s work.

The Proposer: An Advisory Committee to the Standing Committee of the Judicial Conference

The Judicial Conference of the United States is the policymaking organ of the judicial branch of the federal government. Composed of the Chief Justice of the U.S. Supreme Court, the chief judges of the 13 federal judicial circuits, and select federal district judges, it also is required by statute “to carry on a continuous study of the operation and effect of the general rules of practice and procedure" that apply in the federal courts (and, with some variations, in many state court systems as well). The Conference relies on a “Committee on Rules of Practice and Procedure, commonly referred to as the ‘Standing Committee.’" The Standing Committee, in turn, relies on advisory committees on appellate, bankruptcy, civil, criminal, and evidence rules. These advisory committees are comprised of “federal judges, practicing lawyers, law professors, state chief justices, and representatives of the Department of Justice.” (Quotations are from the Administrative Office of the U.S. Courts.) The Advisory Committee on Evidence Rules (which we can abbreviate as ACER) is one of these committees.

The Proposed Text: Two Wording Changes

Rule 702 went into effect in federal courts in 1975. It was one sentence long. The Supreme Court famously interpreted it in Daubert v. Merrell Dow Pharmaceuticals, 509 U.S. 579 (1993), a somewhat ambivalent and abstract opinion. The Court expounded further in cases in 1997 and 1999. The rule was rewritten to incorporate the teachings in these cases in 2000, leading to the version with the longer sentence in the right-hand side of Box 1.

BOX 1. FEDERAL RULE OF EVIDENCE 702 THEN AND NOW
The Rule in 1975	The Rule in 2021
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.	A witness who is qualified as an expert by knowledge, skill, experience, training, or education may testify in the form of an opinion or otherwise if: (a) the expert’s scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue; (b) the testimony is based on sufficient facts or data; (c) the testimony is the product of reliable principles and methods; and (d) the expert has reliably applied the principles and methods to the facts of the case.

The proposed amendment makes two seemingly minor changes, shown in Box 2:

BOX 2. THE ADVISORY COMMITTEE’S PROPOSED AMENDMENT TO RULE 702

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A witness who is qualified as an expert by knowledge, skill, experience, training, or education may testify in the form of an opinion or otherwise if the proponent has demonstrated by a preponderance of the evidence that:
(a) the expert’s scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue;
(b) the testimony is based on sufficient facts or data;
(c) the testimony is the product of reliable principles and methods; and
(d) the expert has reliably applied expert’s opinion reflects a reliable application of the principles and methods to the facts of the case.

Reading these words, one might well ask what is going on. The first change seems to state the obvious (to lawyers, anyway). A footnote in Daubert already indicates that in the “preliminary assessment of whether the reasoning or methodology” possesses “evidentiary reliability,” the trial court must be satisfied by “a preponderance of proof” because that is the threshold for all “[p]reliminary questions concerning the qualification of a person to be a witness, the existence of a privilege, or the admissibility of evidence.” It may not hurt to state this standard in the text of the rule (although including it after the opening clause about qualifications awkwardly fails to modify the qualifications part of the rule). But why bother?

Similarly, the change to Part (d) is potentially confusing because it limits the “reliable application” prong of the rule to expert “opinion” even though, as the Advisory Committee that drafted the original rule noted, it is “logically unfounded” to “assume[] that experts testify only in the form of opinions.” Instead, “[t]he rule … recognizes that an expert on the stand may give a dissertation or exposition of scientific or other principles relevant to the case, leaving the trier of fact to apply them to the facts.” But aside from the probably unintended limitation of the as-applied prong to opinions, why bother? What is the difference between testimony when an expert has “reasonably applied the principles and methods” and testimony that “reflects a reasonable application of the principles and methods”?

The answers lie in ACER’s official note prepared to accompany the rule, the minutes of its meetings, and its periodic reports to the Standing Committee on its progress in revising the rule.

The Purpose of the New Text

For OSAC, the most salient parts of the note of the Advisory Committee are in Boxes 3 and 4. As to the first change, regarding “preponderance,” ACER believed that

BOX 3. Part of ACER’s Proposed Note Explaining Its First Proposed Change

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[M]any courts have held that the critical questions of the sufficiency of an expert’s basis, and the application of the expert’s methodology, are questions of weight and not admissibility. These rulings are an incorrect application of Rules 702 and 104(a). … The Committee concluded that emphasizing the preponderance standard in Rule 702 specifically was made necessary by the courts that have failed to apply correctly the reliability requirements of that rule. … [Explicitly incorporating the standard] means that once the court has found the admissibility requirement to be met by a preponderance of the evidence, any attack by the opponent will go only to the weight of the evidence.

A major push for this change came from individuals and organizations concerned with civil litigation in which, they believed, courts have admitted expert opinions that a drug or chemical is harmful without adequately verifying that there is a body of scientific literature sufficient to let a reasonable expert conclude that the substance can cause the kind of harm claimed to have occurred under the conditions of the case. However, it also will remind judges in criminal cases that they must have proof that the scientific literature is sufficient to support the findings of forensic-science experts.

As Box 4 shows, the second part of the “amendment is especially pertinent to the testimony of forensic [science] experts in both criminal and civil cases”:

BOX 4. Part of ACER’s Proposed Note Explaining Its Second Proposed Change

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Rule 702(d) has also been amended to emphasize that a trial judge must exercise gatekeeping authority with respect to the opinion ultimately expressed by a testifying expert. … The amendment is especially pertinent to the testimony of forensic experts in both criminal and civil cases. Forensic experts should avoid assertions of absolute or one hundred percent certainty—or to a reasonable degree of scientific certainty—if the methodology is subjective and thus potentially subject to error. In deciding whether to admit forensic expert testimony, the judge should (where possible) receive an estimate of the known or potential rate of error of the methodology employed, based (where appropriate) on studies that reflect how often the method produces accurate results. Expert opinion testimony regarding the weight of feature comparison evidence (i.e., evidence that a set of features corresponds between two examined items) must be limited to those inferences that can reasonably be drawn from a reliable application of the principles and methods. This amendment does not, however, bar testimony that comports with substantive law requiring opinions to a particular degree of certainty. … [N]othing in the amendment requires the court to nitpick an expert’s opinion in order to reach a perfect expression of what the basis and methodology can support. The … standard does not require perfection. On the other hand, it does not permit the expert to make extravagant claims that are unsupported by the expert’s basis and methodology.

It is the ACER note, much more than the revisions to the text of the rule, that has implications for forensic-science evidence. As the note indicates, the committee was especially concerned with forensic-science testimony. Its briefing materials included summaries of federal cases from across the spectrum of forensic sciences that raised the issue of “overstatement.” Furthermore, the idea of a new Advisory Committee Note came from the 2016 report of the President’s Council of Advisors on Science and Technology. PCAST called on “the Judicial Conference [to] prepare, with advice from the scientific community, a best practices manual and an Advisory Committee note, providing guidance to Federal judges concerning the admissibility under Rule 702 of expert testimony based on forensic feature-comparison methods.”

Apparently, PCAST did not realize that ACER is not empowered to write new notes to old rules. At a symposium convened by ACER in 2017, PCAST co-chair and newly appointed Presidential science advisor, Eric Lander, advised the committee as follows: “If an advisory note is a possibility, I’d favor it. If it’s not, change a comma in the rule and then write a new advisory note. Change one word, any word and write an advisory note.” Advisory Comm. on Evid. Rules Symposium on Forensic Expert Testimony, Daubert, and Rule 702, 86 Ford. L. Rev. 1463, 1523 (2018). This change-a-word artifice is more or less what is happening.

What Is Next in the Rulemaking Process?

The proposed amendment is just that—proposed. To become law, the ACER amendment and accompanying note must be approved by the Standing Committee after a six-month period for public comment and testimony (after which ACER reviews and can revise the proposed amendment and seek more comment). The Standing Committee then reviews the final drafts. It can revise and return the draft to ACER, or it can submit the amendment and note to the full Judicial Conference for its review. If the Judicial Conference approves, the drafts go to the Supreme Court, which normally transmits them to Congress with no substantive review. Congress then can adopt, reject, modify, or defer the rule change, but if Congress is silent for seven months, the amendment becomes effective at the end of the year.

Plainly, the proposal, which was four years in the making, still has a long way to go, but the very fact that ACER deliberated at length and expressed concern about forensic-science testimony, overstatement, and error probabilities could have more immediate impact in litigation.

Implications for OSAC

To help satisfy the proof requirements of Rule 702 (both as it stands and as it might be amended), subcommittees drafting standards for making findings and for reporting or testifying should specifically cite the scientific literature that supports each part of the standard. Valid estimates of potential error rates (or related statistics on the accuracy of results), or procedures to arrive at these estimates, should be part of such standards. Scientific and Technical Review Panels (STRPs) already are instructed to look for this content or for an explanation in the standard of why methods for ascertaining and expressing uncertainty in measurements, observations, or inferences are not present in the standards they review.

The repeated references to “overstatement” in ACER’s deliberations and materials should reinforce the desire of OSAC units to address the admittedly difficult problem of prescribing standards for testimony—and to use phrases in all standards that involve results that will satisfy the insistence on “those inferences that can reasonably be drawn from a reliable application of the principles and methods.” Cases on firearms-toolmark identifications (called “ballistics” cases in the ACER materials) suggest that judicial efforts are unlikely to produce the best solution. The Department of Justice has attempted to confront this issue with its Uniform Language for Testimony and Reports standards (ULTRs). It argued to ACER that these ULTRs help solve the problem of overclaiming, but one response was that because there are no such standards in laboratories generally, a new Advisory Committee Note is necessary. OSAC units still can help fill this gap if they act quickly.

Disclaimer: This report presents the views of the author. Their publication in In Brief is not an endorsement by NIST or OSAC, and they are not intended to represent the views of any OSAC unit. The error rate associated with them is not known.

Mysteries of the Department of Justice's ULTR for Firearm-toolmark Pattern Examinations

The Department of Justice's Uniform Language for Testimony and Reports (ULTR) for the Forensic Firearms/toolmarks Discipline – Pattern Examination" offers a ready response to motions to limit overclaiming or, to use the pedantic term, ultracrepidarianism, in expert testimony. Citing the DoJ policy, several federal district courts have indicated that they expect the government's expert witnesses to follow this directive (or something like it). \1/

Parts of the current version (with changes from the original) are reproduced in Box 1. \2/ This posting poses three questions about this guidance. Although the ULTR is a step in the right direction, it has a ways to go in articulating a clear and optimal policy.

Box 1. The ULTR

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DEPARTMENT OF JUSTICE
UNIFORM LANGUAGE FOR TESTIMONY AND REPORTS
FOR THE FORENSIC FIREARMS/TOOLMARKS DISCIPLINE –
PATTERN MATCH EXAMINATION ...
III. Conclusions Regarding Forensic Pattern Examination of Firearms/Toolmarks Evidence for a Pattern Match

The An examiner may offer provide any of the following conclusions:

1.Source identification (i.e., identified)
2.Source exclusion (i.e., excluded)
3.Inconclusive

Source identification
‘Source identification’ is an examiner’s conclusion that two toolmarks originated from the same source. This conclusion is an examiner’s decision opinion that all observed class characteristics are in agreement and the quality and quantity of corresponding individual characteristics is such that the examiner would not expect to find that same combination of individual characteristics repeated in another source and has found insufficient disagreement of individual characteristics to conclude they originated from different sources.

The basis for a ‘source identification’ conclusion is an examiner’s decision opinion that the observed class characteristics and corresponding individual characteristics provide extremely strong support for the proposition that the two toolmarks came originated from the same source and extremely weak support for the proposition that the two toolmarks came originated from different sources.

A ‘source identification’ is the statement of an examiner’s opinion (an inductive inference²) that the probability that the two toolmarks were made by different sources is so small that it is negligible. A ‘source identification’ is not based upon a statistically-derived or verified measurement or an actual comparison to all firearms or toolmarks in the world.

Source exclusion
‘Source exclusion’ is an examiner’s conclusion that two toolmarks did not originate from the same source.

The basis for a ‘source exclusion’ conclusion is an examiner’s decision opinion that the observed class and/or individual characteristics provide extremely strong support for the proposition that the two toolmarks came from different sources and extremely weak or no support for the proposition that the two toolmarks came from the same source two toolmarks can be differentiated by their class characteristics and/or individual characteristics.

Inconclusive
‘Inconclusive’ is an examiner’s conclusion that all observed class characteristics are in agreement but there is insufficient quality and/or quantity of corresponding individual characteristics such that the examiner is unable to identify or exclude the two toolmarks as having originated from the same source.

The basis for an ‘inconclusive’ conclusion is an examiner’s decision opinion that there is an insufficient quality and/or quantity of individual characteristics to identify or exclude. Reasons for an ‘inconclusive’ conclusion include the presence of microscopic similarity that is insufficient to form the conclusion of ‘source identification;’ a lack of any observed microscopic similarity; or microscopic dissimilarity that is insufficient to form the conclusion of ‘source exclusion.’

IV. Qualifications and Limitations of Forensic Firearms/Toolmarks Discipline Examinations
• A conclusion provided during testimony or in a report is ultimately an examiner’s decision and is not based on a statistically-derived or verified measurement or comparison to all other firearms or toolmarks. Therefore, an An examiner shall not assert that two toolmarks originated from the same source to the exclusion of all other sources. This may wrongly imply that a ‘source identification’ conclusion is based upon a statistically-derived or verified measurement or an actual comparison to all other toolmarks in the world, rather than an examiner’s expert opinion.

○ assert that a ‘source identification’ or a ‘source exclusion’ conclusion is based on the ‘uniqueness’³ of an item of evidence.

○ use the terms ‘individualize’ or ‘individualization’ when describing a source conclusion.

○ assert that two toolmarks originated from the same source to the exclusion of all other sources.

• An examiner shall not assert that examinations conducted in the forensic firearms/toolmarks discipline are infallible or have a zero error rate.

• An examiner shall not provide a conclusion that includes a statistic or numerical degree of probability except when based on relevant and appropriate data.

• An examiner shall not cite the number of examinations conducted in the forensic firearms/toolmarks discipline performed in his or her career as a direct measure for the accuracy of a proffered conclusion provided. An examiner may cite the number of examinations conducted in the forensic firearms/toolmarks discipline performed in his or her career for the purpose of establishing, defending, or describing his or her qualifications or experience.

• An examiner shall not assert that two toolmarks originated from the same source with absolute or 100% certainty, or use the expressions ‘reasonable degree of scientific certainty,’ ‘reasonable scientific certainty,’ or similar assertions of reasonable certainty in either reports or testimony unless required to do so by a judge or applicable law.³⁴

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² Inductive reasoning (inferential reasoning):

A mode or process of thinking that is part of the scientific method and complements deductive reasoning and logic. Inductive reasoning starts with a large body of evidence or data obtained by experiment or observation and extrapolates it to new situations. By the process of induction or inference, predictions about new situations are inferred or induced from the existing body of knowledge. In other words, an inference is a generalization, but one that is made in a logical and scientifically defensible manner. Oxford Dictionary of Forensic Science 130 (Oxford Univ. Press 2012).

³ As used in this document, the term ‘uniqueness’ means having the quality of being the only one of its kind.’ Oxford English Dictionary 804 (Oxford Univ. Press 2012).
³⁴ See Memorandum from the Attorney General to Heads of Department Components (Sept. 9. 2016), https://www.justice.gov/opa/file/891366/download.

1

Are the two or three conclusions -- identification, exclusion, and inconclusive -- the only way the examiners are allowed to report their results?

In much of the world, examiners are discouraged from reaching only two conclusions--included vs. excluded (with the additional option of denominating the data as too limited to permit such a classification). They are urged to articulate how strongly the data support one classification over the other. Instead of pigeonholing, they might say, for example, that the data strongly support the same-source classification (because those data are far more probable for ammunition fired from the same gun than for ammunition discharged from different guns). 

The ULTR studiously avoids mentioning this mode of reporting. It states that examiners "may provide any of the following ... ." It does not state whether they also may choose not to -- and instead report only the degree of support for the same-source (or the different-source) hypothesis. Does the maxim of expressio unius est exclusio alterius apply? Department of Justice personnel are well aware of this widely favored alternative. They have attended meetings of statisticians at which straw polls overwhelmingly endorsed it over the Department's permitted conclusions. Yet, the ULTR does not list statements of support (essentially, likelihood ratios) as permissible. But neither are they found in the list of thou-shalt-nots in Part IV. \3/ Is the idea that if the examiners have a conclusion to offer, they must state it as one of the two or three categorical ones -- and that they may give a qualitative likelihood ratio if they want to?

2

Is the stated logic of a "source identification" internally coherent and intellectually defensible?

The ULTR explains that "[t]he basis for a 'source identification' is

an examiner’s opinion that the observed class characteristics and corresponding individual characteristics provide extremely strong support for the proposition that the two toolmarks originated from the same source and extremely weak support for the proposition that the two toolmarks originated from different sources.

Translated into likelihood language, the DoJ's "basis for a source identification" is the belief that the likelihood ratio is very large -- the numerator of L is close to one, and the denominator is close to zero (see Box 2). On this understanding, a "source identification" is a statement about the strength of the evidence rather than a conclusion (in the sense of a decision about the source hypothesis). However, the next paragraph of the ULTR states that "[a] ‘source identification’ is the statement of an examiner’s opinion (an inductive inference2) that the probability that the two toolmarks were made by different sources is so small that it is negligible."

Box 2. A Technical Definition of Support The questioned toolmarks and the known ones have some degree of observed similarity X with respect to relevant characteristics. Let Lik(S) be the examiner's judgment of the likelihood of the same-source hypothesis S. This likelihood is proportional to Prob(X | S), the probability of the observed degree of similarity X given the hypothesis (S). For simplicity, we may as well let the constant be 1. Let Lik(D) be the examiner's judgment of the likelihood of the different-source hypothesis (D). This likelihood is Prob(X | D). The support for S is the logarithm of the likelihood ratio L = Lik(S) / Lik(D) = Prob(X | S) / Prob(X | D). \4/

In this way, the ULTR jumps from a likelihood to a posterior probability. To assert that "the probability that the two toolmarks were made by different sources ... is negligible" is to say that Prob(D|X) is close to 0, and hence that Prob(S|X) is nearly 1. However, the likelihood ratio L = Lik(S) / Lik(D) is only one factor that affects Prob(D|X). Bayes' theorem establishes that Odds(D|X) = Odds(D) / L. Consequently, a very large L (great support for S) shrinks the odds in favor of S, but whether we end up with a "negligible" probability for D depends on the odds on D without considering the strength of the toolmark evidence. Because the expertise of toolmark analysts only extends to evaluating the toolmark evidence, it seems that the ULTR is asking them to step outside their legitimate  sphere of expertise by assessing, either explicitly or implicitly, the strength of the particular non-scientific evidence in the case. There is a way to circumvent this objection. To defend a "source identification" as a judgment that Prob(D|X) is negligible, the examiner could contend that the likelihood ratio L is not just very large, as the ULTR's first definition required, but that it is so large that it swamps every probability that a judge or juror reasonably might entertain in any possible case before learning about the toolmarks. A nearly infinite L would permit an analyst to dismiss the posterior odds on D as negligible without attempting to estimate the odds on the basis of other evidence in the particular case (see Box 3).

Box 3. How large must L be to swamp all plausible prior odds? Suppose that the smallest prior same-source probability in any conceivable case were p = 1/1,000,000. The prior odds on the different-source hypothesis would be approximately 1/p = 1,000,000. According to Bayes' rule, the posterior odds on D then would be about (1/p)/L = 1,000,000/L. How large would the support L for S have to be to make D a "negligible" possibility? If "negligible" means a probability below, say 1/100,000, then the threshold value of L (call it L*) would be such that 1,000,000 / L* < 1/100,000 (approximately). Hence L* > 10^11. Are examiners are able to reliably tell whether the toolmarks are such that L > 100 billion? One can use different numbers, of course, but whether the swamping defense of the ULTR really works to justify actual testimony as to "source identification" defined according to the ULTR is none too clear.

The ULTR seems slightly embarrassed with the characterization of a "source identification" as an "opinion" on the small size of a probability. Parenthetically it calls the opinion "an inductive inference," which sounds more impressive. But the footnote that is supposed to explain the the more elegant phrase only muddies the waters. It reads as follows:

Inductive reasoning (inferential reasoning): A mode or process of thinking that is part of the scientific method and complements deductive reasoning and logic. Inductive reasoning starts with a large body of evidence or data obtained by experiment or observation and extrapolates it to new situations. By the process of induction or inference, predictions about new situations are inferred or induced from the existing body of knowledge. In other words, an inference is a generalization, but one that is made in a logical and scientifically defensible manner. Oxford Dictionary of Forensic Science 130 (Oxford Univ. Press 2012) [sic]. \4/

The flaws in this definition are many. First, "inferential reasoning" is not equivalent to "inductive reasoning." Inference is reaching a conclusion from stated premises. The argument from the premises to the conclusion can be deductive or inductive. Deductive arguments are valid when the conclusion is true given that the premises are true. Inductive arguments are sound when the conclusion is sufficiently probable given that the premises are true. Second, inductive reasoning can be based on a small body of evidence as well as on a large body of evidence. In other words, deduction produces logical certainty, whereas induction can yield no more than probable truth. Third, an induction -- that is, the conclusion of an inductive argument -- need not be particularly scientific or "scientifically defensible." Fourth, an inductive conclusion is not necessarily "a generalization." An inductive argument, no less than a deductive one, can go from the general to the specific -- as is the case for an inference that two toolmarks were made by the same source. Presenting an experience-based opinion as the product of "the scientific method" by the fiat of a flawed definition of "inductive reasoning" is puffery.

3

If the examiner has correctly discerned matching "individual characteristics" (as the ULTR calls them), why cannot the examiner "assert that a ‘source identification’ ... is based on ... ‘uniqueness’" or that there has been an "individualization"?

The ULTR states that a "source identification" is based on an examination of "class characteristics" and "individual characteristics." Presumably, "individual characteristics" are ones that differ in every source and thus permit "individualization." The dictionary on which the ULTR relies defines "individualization" as "assigning a unique source for a given piece of physical evidence" (which it distinguishes from "identification"). But the ULTR enjoins an examiner from using "the terms ‘individualize’ or ‘individualization’ when describing a source conclusion," from asserting "that a ‘source identification’ or a ‘source exclusion’ conclusion is based on the ‘uniqueness’ of an item of evidence," and from stating "that two toolmarks originated from the same source to the exclusion of all other sources."

The stated reason to avoid these terms is that a source attribution "is not based on a statistically-derived or verified measurement or comparison to all other firearms or toolmarks." But who would think that an examiner who "assert[s] that two '[t]oolmarks originated from the same source to the exclusion of all other sources'" is announcing "an actual comparison to all other toolmarks in the world"? The examiner apparently is allowed to report a plethora of matching "individual characteristics" and to opine (or "inductively infer") that there is virtually no chance that the marks came from a different source. Allowing such testimony cuts the heart out of the rules against asserting "uniqueness" and claiming "individualization."

NOTES

1. E.g., United States v. Hunt, 464 F.Supp.3d 1252 (W.D. Okla. 2020) (discussed on this blog Aug. 10, 2020).
2. The original version was adopted on 7/24/2018. It was revised on 6/8/2020.
3. Are numerical versions of subjective likelihood ratios prohibited by the injunction in Part IV that "[a]n examiner shall not provide a conclusion that includes a statistic or numerical degree of probability except when based on relevant and appropriate data"? Technically, a likelihood ratio is not a "degree of probability" or (arguably) a statistic, but it seems doubtful that the drafters of the ULTR chose their terminology with the niceties of statistical terminology in mind.
4. A.W.F. Edwards, Likelihood 31 (rev. ed. 1992) (citing H. Jeffreys, Further Significance Tests, 32 Proc. Cambridge Phil. Soc'y 416 (1936)).
5. The correct name of the dictionary is A Dictionary of Forensic Science, and its author is Suzanne Bell. The quotation in the ULTR omits the following part of the definition of "inductive inference": "A forensic example is fingerprints. Every person's fingerprints are unique, but this is an inference based on existing knowledge since the only way to prove it would be to take and study the fingerprints of every human being ever born."

Applying the Justice Department's Policy on a Reasonable Degree of Certainty in United States v. Hunt

In United States v. Hunt, \1/ Senior U.S. District Court Judge David Russell disposed of a challenge to proposed firearms-toolmark testimony. The first part of the unpublished opinion dealt with the scientific validity (as described in Daubert v. Merrell Dow Pharmaceuticals, Inc.) of the Association of Firearms and Toolmark Examiners (AFTE) "Theory of Identification As It Relates to Toolmarks." Mostly, this portion of the opinion is of the form: "Other courts have accepted the government's arguments. We agree." This kind of an opinion is common for forensic-science methods that have a long history of judicial acceptance--whether or not such acceptance is deserved.

The unusual part of the opinion comes at the end. There, the court misconstrues the Department of Justice's internal policy on the use of the phrase "reasonable certainty" to characterize an expert conclusion for associating spent ammunition with a gun that might have fired it. This posting describes some of the history of that policy and suggests that (1) the court may have unwittingly rejected it; (2) the court's order prevents the experts from expressing the same AFTE theory that the court deemed scientifically valid; and (3) the government can adhere to its written policy on avoiding various expressions of "reasonable certainty" and still try the case consistently with the judge's order.

I. The Proposed Testimony

Dominic Hunt was charged with being a felon is possession of ammunition recovered from two shootings. The government proposed to use two firearm and toolmark examiners--Ronald Jones of the Oklahoma City Police Department and Howard Kong of the Bureau of Alcohol, Tobacco, Firearms and Explosives' (ATF) Forensic Science Laboratory--to establish that the ammunition was not fired from the defendant's brother's pistol--or his cousin's pistol. To eliminate those hypotheses, "the Government intend[ed] its experts to testify" that "the unknown firearm was likely a Smith & Wesson 9mm Luger caliber pistol," and that "the probability that the ammunition ... were fired in different firearms is so small it is negligible."

This testimony differs from the usual opinion testimony that ammunition components recovered from the scene of a shooting came from a specific, known gun associated with a defendant. It appears that the "unknown" Luger pistol was never discovered and thus that the examiners could not use it to fire test bullets for comparison purposes. Their opinion was that several of the shell casings had marks and other features that were so similar that they must have come from the same gun of the type they specified.

But the reasoning process the examiners used to arrive at this conclusion--which postulates "class," "subclass," and conveniently designated "individual" characteristics--is the same as the one used in the more typical case of an association to a known gun. Perhaps heartened by several recent trial court opinions severely limiting testimony about the desired individualizing characteristics, Hunt moved "to Exclude Ballistic Evidence, or Alternatively, for a Daubert Hearing."

II. The District Court's Order

Hunt lost. After rejecting the pretrial objection to the scientific foundation of the examiners' opinions and the proper application of accepted methods by the two examiners, Judge Russell turned to the defendant's "penultimate argument [seeking] limitations on the Government's firearm toolmark experts." He embraced the government's response "that no limitation is necessary because Department of Justice guidance sufficiently limits a firearm examiner's testimony."

The odd thing is that he turned the Department's written policy on its head by embracing a form of testimony that the policy sought to eliminate. And the court did this immediately after it purported to implement DoJ's "reasonable" policy. The relevant portion of the opinion begins:

In accordance with recent guidance from the Department of Justice, the Government's firearm experts have already agreed to refrain from expressing their findings in terms of absolute certainty, and they will not state or imply that a particular bullet or shell casing could only have been discharged from a particular firearm to the exclusion of all other firearms in the world. The Government has also made clear that it will not elicit a statement that its experts' conclusions are held to a reasonable degree of scientific certainty.
The Court finds that the limitations mentioned above and prescribed by the Department of Justice are reasonable, and that the Government's experts should abide by those limitations. To that end, the Governments experts:

[S]hall not [1] assert that two toolmarks originated from the same source to the exclusion of all other sources.... [2] assert that examinations conducted in the forensic firearms/toolmarks discipline are infallible or have a zero error rate.... [3] provide a conclusion that includes a statistic or numerical degree of probability except when based on relevant and appropriate data.... [4] cite the number of examinations conducted in the forensic firearms/toolmarks discipline performed in his or her career as a direct measure for the accuracy of a proffered conclusion..... [5] use the expressions ‘reasonable degree of scientific certainty,’ ‘reasonable scientific certainty,’ or similar assertions of reasonable certainty in either reports or testimony unless required to do so by [the Court] or applicable law. \2/

So far it seems that the court simply told the government's experts (including the city police officer) to tow the federal line. But here comes the zinger. The court abruptly turned around and decided to ignore the Attorney General's mandate that DoJ personnel should strive to avoid expressions of "reasonable scientific certainty" and the like. The court wrote:

As to the fifth limitation described above, the Court will permit the Government's experts to testify that their conclusions were reached to a reasonable degree of ballistic certainty, a reasonable degree of certainty in the field of firearm toolmark identification, or any other version of that standard. See, e.g., U.S. v. Ashburn, 88 F. Supp. 3d 239, 249 (E.D.N.Y. 2015) (limiting testimony to a “reasonable degree of ballistics certainty” or a “reasonable degree of certainty in the ballistics field.”); U.S. v. Taylor, 663 F. Supp. 2d 1170, 1180 (D.N.M. 2009) (limiting testimony to a “reasonable degree of certainty in the firearms examination field.”). Accordingly, the Government's experts should not testify, for example, that “the probability the ammunition charged in Counts Eight and Nine were fired in different firearms is so small it is negligible” ***.

So the experts can testify that they have "reasonable certainty" that the ammunition was fired from the same gun, but they cannot say the probability that it was fired from a different gun is small enough that the alternative hypothesis has a negligible probability? Even though that is how experts in the field achieve "reasonable certainty" (according to the AFTE description that the court held was scientifically valid)? This part of the opinion hardly seems coherent. \3/

III. The Tension Between the Order and the ULTR

The two cases that the court cited for its "reasonable ballistic certainty" ruling were decided years before the ULTR that it called reasonable, and such talk of "ballistic certainty" and "any other version of that standard" is precisely what the Department had resolved to avoid if at all possible. The history of the "fifth limitation" has an easily followed paper trail that compels the conclusion that this limitation was intended to avoid precisely the kind of testimony that Judge Russell's order permits.

Let's start with the ULTR quoted (in part) by the court. It has a footnote to the "fifth limitation" that instructs readers to "See Memorandum from the Attorney General to Heads of Department Components (Sept. 9. 2016), https://www.justice.gov/opa/file/891366/download." The memorandum's subject is "Recommendations of the National Commission on Forensic Science; Announcement for NCFS Meeting Eleven." In it, Attorney General Loretta Lynch wrote:

As part of the Department's ongoing coordination with the National Commission on Forensic Science (NCFS), I am responding today to several NCFS recommendations to advance and strengthen forensic science. *** I am directing Department components to *** work with the Deputy Attorney General to implement these policies *** .

1. Department forensic laboratories will review their policies and procedures to ensure that forensic examiners are not using the expressions "reasonable scientific certainty" or "reasonable [forensic discipline] certainty" in their reports or testimony. Department prosecutors will abstain from use of these expressions when presenting forensic reports or questioning forensic experts in court unless required by a judge or applicable law.

The NCFS was adamant that judges should not require "reasonable [forensic discipline] certainty." Its recommendation to the Attorney General explained that

Forensic discipline conclusions are often testified to as being held “to a reasonable degree of scientific certainty” or “to a reasonable degree of [discipline] certainty.” These terms have no scientific meaning and may mislead factfinders about the level of objectivity involved in the analysis, its scientific reliability and limitations, and the ability of the analysis to reach a conclusion. Forensic scientists, medical professionals and other scientists do not routinely express opinions or conclusions “to a reasonable scientific certainty” outside of the courts. Neither the Daubert nor Frye test of scientific admissibility requires its use, and consideration of caselaw from around the country confirms that use of the phrase is not required by law and is primarily a relic of custom and practice. There are additional problems with this phrase, including:

• There is no common definition within science disciplines as to what threshold establishes “reasonable” certainty. Therefore, whether couched as “scientific certainty” or“ [discipline] certainty,” the term is idiosyncratic to the witness.
• The term invites confusion when presented with testimony expressed in probabilistic terms. How is a lay person, without either scientific or legal training, to understand an expert’s “reasonable scientific certainty” that evidence is “probably” or possibly linked to a particular source?

Accordingly, the NCFS recommended that the Attorney General "direct all attorneys appearing on behalf of the Department of Justice (a) to forego use of these phrases ... unless directly required by judicial authority as a condition of admissibility for the witness’ opinion or conclusion ... ." As we have seen, the Attorney General adopted this recommendation. \4/

IV. How the Prosecutors and the ATF Expert Can Follow Departmental Policy

Interestingly, Judge Russell's opinion does not require the lawyers and the witnesses to use the expressions of certainty. It "permits" them to do so (seemingly on the theory that this practice is just what the Department contemplated). But not all that is permitted is required. To be faithful to Department policy, the prosecution cannot accept the invitation. The experts can give their conclusion that the ammunition came from a single gun. However, they should not add, and the prosecutor may not ask them to swear to, some expression of "reasonable [discipline] certainty" because: (1) the Department's written policy requires them to avoid it "unless required by a judge or applicable law"; (2) the judge has not required it; and (3) applicable law does not require it. \5/

The situation could change if at the trial, Judge Russell were to intervene and to ask the experts about "reasonable certainty." In that event, the government should remind the court that its policy, for the reasons stated by the National Commission and accepted by the Attorney General, is to avoid these expressions. If the court then rejects the government's position, the experts must answer. But even then, unless the defense "opens the door" by cross-examining on the meaning of "reasonable [discipline] certainty," there is no reason for the prosecution to use the phrase in its examination of witnesses or closing arguments.

NOTES

1. No. CR-19-073-R, 2020 WL 2842844 (W.D. Okla. June 1, 2020).
2. The ellipses in the quoted part of the opinion are the court's. I have left out only the citations in the opinion to the Department's Uniform Language on Testimony and Reporting (ULTR) for firearms-toolmark identifications. That document is a jumble that is a subject for another day.
3. Was Judge Russell thinking that the "negligible probability" judgment is valid (and hence admissible as far as the validity requirement of Daubert goes) but that it would be unfairly prejudicial or confusing to give the jury this valid judgment? Is the court's view that "negligible" is too strong a claim in light of what is scientifically known? If such judgments are valid, as AFTE maintains, they are not generally prejudicial. Prejudice does not mean damage to the opponent's case that arises from the very fact that evidence is powerful.
4. At the NCFS meeting at which the Department informed the Commission that it was adopting its recommendation, "Commission member, theoretical physicist James Gates, complimented the Department for dealing with these words that 'make scientists cringe.'" US Dep't of Justice to Discourage Expressions of "Reasonable Scientific Certainty," Forensic Sci., Stat. & L., Sept. 12, 2016, http://for-sci-law.blogspot.com/2016/09/us-dept-of-justice-to-discourage.html.
5. In a public comment to the NCFS, then commissioner Ted Hunt (now the Department's senior advisor on forensic science) cited the "ballistic certainty" line of cases as indicative of a problem with the NCFS recommendation as then drafted but agreed that applicable law did not require judges to follow the practice of insisting on or entertaining expressions of certitude. See "Reasonable Scientific Certainty," the NCFS, the Law of the Courtroom," and That Pesky Passive Voice, Forensic Sci., Stat. & L., http://for-sci-law.blogspot.com/2016/03/reasonable-scientific-certainty-ncfs.html, Mar. 1, 2016; Is "Reasonable Scientific Certainty" Unreasonable?, Forensic Sci., Stat. & L., Feb. 26, 2016, http://for-sci-law.blogspot.com/2016/02/is-reasonable-scientific-certainty.html (concluding 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.)