Sound Science in an Adversarial System: The Gatekeepers of Scientific Evidence in the Courts

Sound Science in an Adversarial System: The Gatekeepers of Scientific Evidence in Court

This entry is part of a series on the role of science in the federal judiciary. Read the first post in the series HERE.

Scientists need thick skin to successfully navigate the seemingly endless series of critique from peer reviews, post-presentation Q&As, and  Pubpeer comments. But this lengthy process is essential to science today. With each pass, scientists engage with the research using a critical eye, thus helping to establish scientific fact. Through this process, claims with major conflicts of interest, biases, or errors can be debunked.

In the courtroom, however, the ones who are engaging with the research are adversarial parties whose primary responsibility is to advocate for their own position. An ideal peer review has scientists identifying errors, checking that appropriate methods were used, and ensuring that the research is high quality. But legal practitioners in a courtroom do not necessarily have the same goal.  They are advocates trying to establish facts that support their specific argument. All of this happens on a timeline of a few months or years at most; there is no time to let decades of the iterative process of science play out.

Instead, it falls on judges to ensure that scientific evidence and expert testimony is grounded in reliable methods and broadly accepted in the scientific community. This role as a “gatekeeper” was clarified in the Supreme Court decision of Daubert v. Merrell Dow Pharmaceuticals, 1993.[1] In this landmark case, the Daubert family ended up at the Supreme Court after alleging that a Dow Pharmaceutical medication given to the mother in pregnancy had caused serious birth defects in their child. In the initial arguments, expert witnesses presented a reanalysis of peer-reviewed epidemiology and toxicology studies to support their argument. Although the lower courts relied upon this testimony, the Supreme Court ultimately found the reanalysis inadmissible and suggested a non-exhaustive set of criteria for judges to consider when admitting science into evidence. Judges were instructed to consider:

• If the technique or theory had been tested;
• If it had been peer-reviewed;
• Its known error-rate;
• Any known standards of procedures; and
• If it was broadly accepted by the scientific community.

This standard was encoded into the 2000 amendment of the Federal Rule of Evidence 702, a rule still in use today.[2] In this way, judges must fulfill a role somewhat like an anonymous peer reviewer, ensuring that methods of scientific evidence are reliable and acceptable.

Yet this guidance does not guarantee that the courts are protected from faulty “science” that has not been subject to the iterative and lengthy scientific process. For example, bitemarks used to be acceptable evidence to help identify a suspect, but this method was never valid.[3] Testifying experts claimed that a person’s dental features were uniquely identifiable, but a 2023 review of actual scientific studies around bitemark identification found no evidence supporting this claim.[4]

More recently, legal evidence around Shaken Baby Syndrome has been re-examined. Shaken Baby Syndrome occurs when an infant or toddler is forcefully shaken, which can result in irreversible brain damage or death. About [1] [2] 1,300 cases of Shaken Baby Syndrome are reported in hospitals yearly, and prosecution typically follows. But for some of the accused parents and caregivers, Shaken Baby Syndrome is diagnosed based on vomiting, seizures, or other symptoms in the absence of other signs of abuse. Today, the consensus on signs of abuse in Shaken Baby Syndrome is being questioned. There is now a growing opinion that the standards used to ascertain abuse in a Shaken Baby Syndrome case are inadequate or even wrong.[5] Scientists and legal practitioners say that this misstep could have resulted in parents being wrongly convicted of abusing their child, when a fall or other underlying condition was the actual cause of their injuries. In 2024, over thirty people have been exonerated of charges related to Shaken Baby Syndrome.

The role of science in the courtroom is complex, especially because the purposes and practices of science and law differ. Scientists bear the responsibility to ensure that studies are conducted with integrity, transparency, and high standards. In turn, the gatekeepers of the courtroom bear the responsibility to safeguard the courtroom against faulty science. Together, these roles function to help factfinders reveal sound conclusions in life beyond the laboratory bench.

[1] Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U. S. 579 (1993)

[2] See Federal Rules of Evidence Rule 702 and Congressional Package Proposed Amendments to the Federal Rules of Evidence (2023). https://www.uscourts.gov/sites/default/files/2023_congressional_package_april_24_2023_0.pdf

[3] Executive Office of the President of the United States, President’s Council of Advisors on Science and Technology. Report to the President, Forensic Science in Criminal Courts: Ensuring Scientific Validity of Feature-Comparison Methods (2016).

[4] Sauerwein, K. et al. Bitemark Analysis: A NIST Scientific Foundation Review, NIST Interagency Report, NIST IR 8352, (2023), DOI: 10.6028/NIST.IR.8352.

[5] See Tuerkheimer, D. The Next Innocence Project: Shaken Baby Syndrome and the Criminal Courts, 87 Washington University Law Review (2009); Wasserman, J.D. Science as Superstition: A Model Statute for Changed Science Claims, 73 Duke Law Journal (2023).

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