Saturday, September 24, 2016

The PCAST Report and Argumentum Ad Hominem

I suppose it was inevitable. If you don't like the message, just dismiss the messengers as ill-informed or biased. Toss in a few simplistic generalities, and some praise for the people who agree with you, and, voila, you can avoid trying to analyze of the substantive basis for the message. This dynamic is at work in the reactions to the report of the President's Council of Advisors on Science and Technology (PCAST) on forensic science. I'll give two examples — one from a pro-report commentator, and another from an anti-report group.

On the pro-report side, we have Randy Balko writing on the Washington Post website that the PCAST report should be seen as scientifically correct because it is written by "people such as Eric Lander, a geneticist, biologist and mathematician at the Massachusetts Institute of Technology; Sylvester James Gates Jr., who studies superstring theory and particle physics at the University of Maryland; Susan Graham, acclaimed computer scientist at the University of California at Berkeley; and William H. Press, an astrophysicist, theoretical physicist, computer scientist and computational biologist at the University of Texas." 1/ In contrast, the prosecutors who attacked PCAST's assessments of the scientific literature in a press release a few weeks ago are "district attorneys — people who work in an adversarial profession; who have achieved great success in a field where rhetoric and persuasion are just as if not more important than facts (remember, most DAs are elected) [and their] ability to win convictions stands to get much more difficult should these disciplines be barred from the courtroom."

Now this is not a fallacious argumentum ad hominem. Everything else being equal, it is rational to believe scientists' views about science over lawyers'. But the acclaim that individuals have achieved in other fields of science is not a sure guide to the validity of their judgments of the scientific foundations of various techniques and theories. William Shockley's outstanding work on electrons and holes in semiconductors did not lend substantive weight to his arguments on intelligence, heredity, and race. The contribution of biochemist Kary Mullis — another Nobel Laureate — to PCR amplification reveals little about the truth of his views on the scientific foundations of climate change, ozone depletion, and the cause of AIDS. 2/

This is not to say that the reputation of a scientist has nothing to do with the reception of his or her ideas. Neither is it a comparison of any one scientist to another or a claim that the PCAST report is mistaken. It is simply a statement that the authority proposing an idea or making an argument matters more to lawyers than it does (or, more precisely, than it should) to scientists. In science, "arguments from authority are worthless," or so it has been said. 3/ Given this Galilean ideal, 4/ one would hope that the responses to the PCAST report from forensic scientists either would concur with PCAST's observations or reject them in the light of a more thorough or more perceptive  study of the foundational literature.

So far, I have not seen such responses — although it is way too early to expect to find them. Instead, one group of forensic scientists have spoken out against the report by taking the unscientific tack of ad hominem argumentation. At least, this is a prominent feature of the Position Statement of the American Congress of Forensic Science Laboratories. 5/ These forensic scientists had this to say about the report:
Unfortunately, it was born of an imbalanced and inexperienced working group whose make-up included no forensic practitioners nor any other professionals with demonstrated experience in the practice of forensic science. The Chair of the aforementioned working group, Eric Lander, sits on the Board of Directors of the Innocence Project, a legal-activism group that has itself been publicly criticized on numerous occasions (including within peer reviewed literature) for the unfairness of its public statements and the conflicts of interest that have long called into question its motives. In addition, the working group’s writer, Tania Simoncelli,4 has publicly authored previous opinions that DNA database collections violate civil liberties.5
The argument in the first sentence that a competent literature review cannot be written by a group of scientists that does not include "forensic practitioners" or "professionals [who] practice ... forensic science" is the mark of an insular guild that resists scientific norms. Anyone skilled in empirical research methods and statistics should be able to survey and comment on the state of the science. "Just as an epidemiologist who does not treat patients may be qualified to testify to the state of the scientific proof of a chemical’s toxicity, a scientist with expertise in research methods and statistics need not be an expert in the details of toolmark examinations to determine whether the scientific literature supports a practitioner’s professed abilities." 6/

The remainder of the polemic "is not [there] to disparage any individuals or their motives," but it is hard to see how else it is relevant. I have disagreed with some of the legal, scientific, and policy positions espoused by Tania Simoncelli, 7/ but a person's views on controversial issues such as the constitutionality of DNA sampling on arrest — a procedure that four U.S. Supreme Court Justices insisted was unconstitutional — hardly makes someone unsuitable as a technical writer. Finally, the idea that a co-chair of the PCAST working group is tainted by an association with the Innocence Project — an advocacy group that itself relies on forensic science — is about as far from a substantive critique as one can get.

Forensic scientists who want to show that parts of the PCAST report are flawed will have to resist the temptation to dismiss the report as "a political phenomenon" born of "ignoran[ce] of the ugly realities associated with solving crimes like murder and rape as quickly and accurately as possible." 8/ They will have to respond in a scientifically defensible manner.

  1. Randy Balko, White House Science Council: Bite-mark Matching Is Junk Science, The Watch, Sept. 7, 2016,
  2. Even within the fields in which a given scientist has made important contributions, examples of erroneous judgments from that scientist are commonplace. Arguably, Eric Lander's conclusions about "spectacular deviations from Hardy-Weinberg, indicating the presence of genetically distinct subgroups" in People v. Castro, an early DNA-evidence case noted in the PCAST report, falls into this category. See David H. Kaye, The Double Helix and the Law of Evidence 115-20 (2010). Even Albert Einstein made his share of mistakes in physics and mathematics. Hans C. Ohanian, Einstein's Mistakes: The Human Failings of Genius (2008).
  3. Carl Sagan, Cosmos 277 (1985).
  4. "In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual." Galileo Galilei, as quoted in Fran├žois Arago, Biographies of Distinguished Scientific Men 365 (1859).
  5. American Congress of Forensic Science Laboratories, Position Statement, Sept. 21, 2016,
  6. David H. Kaye et al., The New Wigmore on Evidence: Expert Evidence § 373 (Cum. Suppl. 2016). The better reasoned judicial opinions on the qualifications of expert witnesses to testify to their reviews adopt this approach. E.g., State v. Romero, 365 P.3d 358, 362 (Ariz. 2016).
  7. See, e.g., Hot Off the Presses: Chimeric Criminals, Forensic Sci., Stat. & L., Mar. 23, 2013,; "Genetic Justice": The Potential and the Real, Forensic Sci., Stat. & L., June 6, 2011,
  8. Position Statement, supra note 5.
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