Call for Evidence-Based Medicine in Medical Expert Opinions

Evidence-based medicine (EBM) seeks to put health care decision making on a firm epistemic foundation, rather than on the personal opinion of health care providers.  David Sackett, et al., “Evidence based medicine: what it is and what it isn’t,” 312 Brit. Med. J. 71 (1996).  EBM thus offers a therapeutic intervention, sometimes in the form of strong medicine, to the sloppy thinking, intuition, mothers’ hunches, and leveling of studies that remain prevalent in the Rule 702 gatekeeping of medical causation opinion testimony in courts.  There are some who have suggested that EBM addresses therapeutic interventions only, and not disease causation by exogenous substances or processes.  A very recent publication in the Tort Trial & Insurance Practice Law Journal provides a strong rebuttal to the naysayers and a clear articulation of the need now, more than ever, for greater acknowledgment of EBM in the evaluation of expert witness opinion testimony.  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 Tort Trial & Ins. Practice L. J. 741 (2012) [cited as Davidson].

Terence M. Davidson is a physician, a Professor of Surgery, and the Associate Dean for Continuing Medical Education at the University of California, San Diego School of Medicine.  Christopher P. Guzelian   is an Assistant Professor of Law at Thomas Jefferson School of Law, in San Diego, California. Davidson and Guzelian bring the Rule 702 discussion and debate back to the need for epistemic warrant, not glitz, glamour, hunches, prestige, and the like.  Their article is a valuable contribution, and the authors’ presentation and defense of EBM in the gatekeeping process is commendable.

There are some minor dissents I would offer.  For instance, in applying EBM principles to causation of harm assessments, we should recognize that there are asymmetries between determining therapeutic benefit and environmental or occupational harm.  Physicians, even those practicing EBM, may well recommend removal from a potentially toxic exposure because the very nature of their clinical judgment is often precautionary.  Tamraz v. BOC Group Inc., No. 1:04-CV-18948, 2008 WL 2796726 (N.D. Ohio July 18, 2008) (denying Rule 702 challenge to treating physician’s causation opinion), rev’d sub nom., Tamraz v. Lincoln Elec. Co., 620 F.3d 665, 673 (6th Cir. 2010) (carefully reviewing record of trial testimony of plaintiffs’ treating physician; reversing judgment for plaintiff based in substantial part upon treating physician’s speculative causal assessment created by plaintiffs’ counsel; “Getting the diagnosis right matters greatly to a treating physician, as a bungled diagnosis can lead to unnecessary procedures at best and death at worst. But with etiology, the same physician may often follow a precautionary principle: If a particular factor might cause a disease, and the factor is readily avoidable, why not advise the patient to avoid it? Such advice—telling a welder, say, to use a respirator—can do little harm, and might do a lot of good. This low threshold for making a decision serves well in the clinic but not in the courtroom, where decision requires not just an educated hunch but at least a preponderance of the evidence.”) (internal citations omitted), cert. denied, ___ U.S. ___ , 131 S. Ct. 2454, 2011 WL 863879 (2011).

The wisdom of the Tamraz decision (in the 6th Circuit) lies in its recognition of the asymmetries involved in medical decision making.  For most diseases, physicians rarely have to identify an etiology to select efficacious treatment.  This asymmetry affects the general – specific causation distinction.  A physician will want some epistemic warrant for the judgment that a therapy or medication is efficacious.  In other words, the physician needs to know that there is efficacy, even though the intervention may not be efficacious in every case.  If the risk ratio for an intervention (where the risk is cure of the disease or disorder), is greater than 1.0, and chance, bias, and confounding are eliminated as explanations for the observed efficacy, then that intervention likely goes into the physician’s therapeutic armamentarium.  The risk ratio, of course, need not be greater than two for the intervention to remain clinically attractive.  Furthermore, if the therapy is provided, and the patient improves, the determination whether therapy itself was efficacious is often not a pressing clinical matter.  After all, if the risk ratio was greater than one, but two or less, then the improvement may have been spontaneous and unrelated to therapy.

Davidson and Guzelian do not fully recognize this asymmetry, which leads the authors into error.  They give an example in which a defense expert witness proferred a personal opinion about general causation of breast cancer by post-menopausal hormone replacement therapy, which opinion is undermined and contradicted by a judgment reached with EBM principles.  See Cross v. Wyeth Pharm., Inc., 2011 U.S. Dist. LEXIS 89078, at *10 (M.D. Fla. Aug. 10, 2011).  Fair enough, but Davidson and Guzelian then claim that the errant defense expert had no basis for claiming that there was no generally accepted basis for “diagnosing specific medical causation.” Davidson at 757.  The authors go even further and claim that the defense expert’s statement is “simply false.” Id.

I would suggest that the authors have gotten this dead wrong.  In this sort of case, the plaintiff’s expert witness is usually the one casting about for a basis to support specific attribution.  The authors offer no basis for their judgment that the defense expert witness is wrong, or lacks a basis for his specific causation judgment. The poor, pilloried defense expert was, in the cited case, opining that there was no way to attribute a particular patient’s breast cancer to her prior use of post-menopausal hormone replacement therapy.  Putting aside the possibility of long-term use (with risk ratio greater than 2.0), the expert’s opinion is reasonable. General causation does not logically or practically imply specific causation; they are separate and distinct determinations.  Perhaps a high risk ratio might justify a probabilistic inference that the medication caused the specific patient’s breast cancer, but for many HRT-use factual scenarios, the appropriate risk ratio is two or less.  If there is some other method Davidson and Guzelian have in mind, they should say so. The authors miss an important point, which is that EBM sets out to provide a proper foundation for judgments of causality (whether of therapeutic benefit or harm), but it often does not have the epistemic foundation to provide a resolution of the individual causation issue. In medicine, there often is simply no need to do so.

One other nit.  The authors briefly discuss statistical significance, citing the Supreme Court’s recent foray into statistical theory.  Davidson at 747 & n. 14 (citing Matrixx Initiatives, Inc. v. Siracusano, 131 S. Ct. 1309, 1321 (2011)).  In their explanatory parenthetical, however, the authors describe the case as “holding that a lack of statistical significance in a pharmaceutical company’s results does not exempt the company from material disclosure requirements for reporting adverse events during product testing.”  Id. 

Matrixx Initiatives held no such thing; the Supreme Court was faced with an adequacy of pleadings case. No evidence was ever offered; nor was there any ruling on the reliability or insufficiency of evidence of causation. Matrixx Initiative’s attempt to import Rule 702 principles of reliability into a motion to dismiss on the pleadings was seriously misguided. Even assuming that statistical significance was necessary to causation, regulatory action did not require a showing of causality. Therefore, statistical significance was never necessary for the plaintiffs’ case. Second, the company’s argument that the adverse event reports at issue were “not statistically significant” was fallacious because adverse event reports, standing alone, could not be “statistically significant” or “insignificant.” The company would need to know the expected base rate for anosmia among Zicam users, and it would need to frame the adverse event reports in terms of an observed rate, so that the expected and observed rates could be compared against an assumption of no difference. Third, the class plaintiffs had alleged considerably more than just the adverse events, and the allegations taken together deserved the attention of a reasonable investor.  Bottom line:  the comments that the Court made about the lack of necessity for statistical significance were pure obiter dictum.

Highlighting these two issues in the Davidson & Guzelian article should not detract from the importance of the authors’ general enterprise. There is an aversion to examining the “epistemic warrant” behind opinion evidence in federal court gatekeeping.  Anything that treats that aversion, such as Davidson & Guzelian’s article, is good medicine.

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