Evidence Commentary 130 Harv. L. Rev. F. 127

Hypothesis Testing in Law and Forensic Science: A Memorandum

Forensic Commentary Series



This Forum Commentary series presents views on a memorandum from a group of lawyers and judges advising the Organization of Scientific Area Committees for Forensic Science (OSAC).1 In response to calls for improving the practices of forensic science,2 the National Institute of Standards and Technology (NIST) created the Scientific Area Committees in 2014 to promote and develop standards “that are fit-for-purpose and based on sound scientific principles.”3 The memorandum from the Legal Resource Committee (LRC)4 responds to a question from a scientist on OSAC’s governing board about whether the criminal law’s concern with avoiding false convictions at the expense of false acquittals should affect the choice of a “significance level” for deciding whether pieces of glass match in their chemical composition (and hence might have a common origin). Must a criminalist favor the hypothesis that similarities are coincidental over the hypothesis that the fragments have a common origin? The underlying issue applies to many forms of identification evidence, including fingerprints, fibers, paint chips, bullets, and biological fluids. Indeed, arguments over the choice of a significance level arise for statistical evidence of all sorts, from econometrics to epidemiology.5

This Introduction is a preamble to the memorandum. Part I describes the technical standard that prompted the memorandum. Part II sketches the statistical ideas in the memorandum by using glass comparisons to illustrate the three main statistical approaches to reasoning about the implications of evidence. This Introduction is followed by the memorandum itself and two commentaries.

* Associate Dean for Research and Distinguished Professor of Law, Penn State Law. This Introduction benefited from discussions with José Almirall, Karen Kafadar, and members of the Legal Resource Committee (LRC) of the Organization of Scientific Area Committees for Forensic Science (OSAC). The views expressed here are the author’s. They should not be attributed to NIST, OSAC, the LRC, or any other individual or organization.

  1. ^ See Memorandum from the Legal Res. Comm. to the Org. of Sci. Area Comms. for Forensic Sci., Nat’l Inst. of Standards & Tech., Question on Hypothesis Testing in ASTM 2926-13 and the Legal Principle that False Convictions Are Worse than False Acquittals 6 (rev ed. Oct. 7, 2016), reprinted in 130 Harv. L. Rev. F. 137 (2017) [hereinafter LRC Memo].

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  2. ^ See, e.g., Comm. on Identifying the Needs of the Forensic Sci. Cmty., Nat’l Research Council, Strengthening Forensic Science in the United States: A Path Forward 53 (2009).

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  3. ^ About OSAC, OSAC Newsletter (Nat’l Inst. of Standards & Tech., Gaithersburg, Md.), Oct. 2015, at 3, 3, https://www.nist.gov/sites/default/files/documents/forensics/OSACNewsLetterOctober2015.pdf [https://perma.cc/29QA-XRJC].

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  4. ^ When the memorandum was written, the LRC was composed of ten individuals from prosecutor and public defender offices, the judiciary, the Innocence Project, and law school faculty. The LRC comments on proposed standards and advises OSAC on legal issues. The scientific committees need not follow the LRC’s recommendations or give effect to its opinions. OSAC-approved standards go to private standards-development organizations for possible adoption (perhaps with modifications). If OSAC approves of standards adopted by these external groups, NIST incorporates them into a registry of approved standards. For more information about the LRC, see OSAC Roles and Responsibilities, Nat’l Inst. Standards & Tech. (Jan. 26, 2016), https://www.nist.gov/forensics/osac-roles-and-responsibilities [https://perma.cc/3V99-CJ5L]. How much influence these standards will have on forensic laboratories, courts, or legislatures remains to be seen.

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  5. ^ See, e.g., David H. Kaye et al., The New Wigmore: A Treatise on Evidence: Expert Evidence § 12.8.3, at 563–64 (2d ed. 2011).

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