Two Schools of Thought for Warning Standards

In products liability litigation over designs and warnings, a supplier or manufacturer is typically held to the knowledge and expertise of an expert in the relevant field. Experts, especially in the early days of understanding a newly identified putative risk, may disagree on the quality and quantity of evidence in support of the claimed risk. And of course they may dispute whether the claimed risk exists at all, or the criteria by which the risk should be established. Unfortunately, the law offers little help in answering the obvious question of which expert or group of experts, and which criteria, of all the experts and criteria in the world, are the appropriate reference standards. The point of adverting to experts is, no doubt, that the law knows nothing about causal claims unless there is admissible and sufficient evidence of the risk, typically from a qualified expert, serving as an expert witness, who proffers an opinion about causal claim.

The standard formulation evades the necessity of confronting the epistemic standard for knowledge of the risk by pointing to some expert’s or group of experts’ opinion. Rather than looking directly at whether the causal claim is “true, justified belief,” the law asks whether expert witnesses hold such opinions. This maneuver has several inherent risks of its own. First, it transmutes factfinding into an exercise in the sociology or sampling of expert witnesses. In the case of claims that involve long latencies between the exposure to the putative risk and the manifestation of harm, this sociological exercise becomes one of intellectual history. One of the reasons that the Frye standard was so difficult in practice was its insistence that courts ascertain whether a particular claim or a use of scientific device was “generally accepted.” The assessment of the relevant expert’s knowledge of risk has generally not gone well in litigation contexts. Second, the maneuver of looking to experts’ opinions introduces a different kind of risk; that is, the maneuver risks diluting the standard for warning, “knowledge and expertise” to subjective opinion, hunches, conjecture, and the like.

An analogue of the standard for warning of risks may be found in the law of medical malpractice. Historically, American law relied heavily upon generally held opinions as the measure of knowledge, which were incorporated into standards of reasonable professional care. The law that governs litigation over the quality of medical care in many states resolves this issue by providing a defense under the “Two Schools of Thought Doctrine.”[1] A physician does not deviate from the standard of care simply because many or even most physicians reject the approach he or she took in the care and treatment of the aggrieved patient’s problem. As long as a substantial minority of physicians would have concurred in the judgment of the defendant physician, the claim of malpractice fails.

Pennsylvania confronted the nose-counting problem in Jones v. Chidester, by passing the buck to the jury. The Pennsylvania Supreme Court held that a physician would escape liability if his medical treatment received the support of a “considerable number” of medical experts.[2] The court allocated to the jury the factual determination how many recognized and respected medical experts were needed to create a “school of thought,” but it left completely unclear how a jury would make such a determination.[3]

The law’s lassitude in relying upon professional custom and opinion, rather than whether the custom had sound evidentiary and methodological foundations, might be taken as deference to, and protection of, the medical profession. Or, less charitably, this reliance might be taken as intellectual laziness to avoid engagement with the intellectual basis for the custom or the school of thought. Indeed, the continuing validity of the “nose-counting” approach may certainly be questioned in the era of “evidence-based medicine,” which rejects custom as the basis for medical interventions in favor of the novelty of evidence itself.[4]

If the Two Schools Doctrine should be good law, it has obvious implications for the standard of design or warning in products cases, as well as for the standard of causation. How can a judge or jury impose liability upon a manufacturer for failing to warn about a risk that “a school of thought” among scientists believes is not a risk? An even more extreme disparity arises when the jury or judge comes to the belief that a manufacturer deserves to be punished for failing to warn about supposed risks when many scientists and even regulators do not believe exist.

It is a mystery.


[1]        See, e.g., MacDonald v. United States, 767 F. Supp. 1295, 1308 (M.D. Pa. 1991) (outlining the history and development of the two-schools doctrine under Pennsylvania law); Young v. United States, 574 F. Supp. 571, 581 (D. Del. 1983) (holding that medical profession’s acceptance of alternative appropriate remedies is a complete defense to claim of negligence for failing to use another remedy);  Scheuler v. Strelinger, 204 A.2d 577, 204 A.2d 577, 585  (1964).

[2]        Jones v. Chidester, 531 Pa. 31, 610 A.2d 964, 967 (1992).

[3]        See, e.g., Dailey, “The Two Schools of Thought and Informed Consent Doctrine in Pennsylvania,” 98 Dickenson L. Rev. 713 (1994); Douglas Rader Brown, “Panacea or Pandora’s Box: The ‘Two Schools of Medical Thought’ Doctrine after Jones v. Chidester, 610 A.2d 964 (Pa. 1992),” 44 J. Urban & Contemp. Law 223 (1993).

[4]           See Terence M. Davidson & Christopher P. Guzelian, “Evidence-Based Medicine (EBM): The (Only) Means for Distinguishing Knowledge of Medical Causation from Expert Opinion in the Courtroom,” 47 Trial & Insur. Prac. L. J. 741 (2012) (discussing the advent of evidence-based medicine and its implications for medical education an practice).

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