• The False Equivalence Motion: A trend in Plaintiffs' Offensive Use of Daubert Challenges
  • May 3, 2017 | Author: Andrew H. Myers
  • Law Firm: Wheeler Trigg O'Donnell LLP - Denver Office
  • DRI's RX for the Defense

    Beware Daubert challenges that attempt to shift the causation burden to the defense through artful inversion, suggesting the defense must prove a medication does not cause harm. Even if unlikely to result in exclusion of defense experts (assuming experts are prepared to deal with burden shifting attempts at deposition) these motions may imperil effective Daubert challenges to plaintiff experts.

    “Defendants not only have to prove [alternative causation], but also that the putative [alternative cause] is the proximate and sole cause of [the plaintiff’s] alleged injury. This proof must come from qualified experts and it must be relevant as well as scientifically reliable.” These remarkable claims concerning the defendant’s supposed burden to disprove causation crossed my desk recently in a plaintiff’s Daubert motion. I was reminded of another Daubert motion filed against our causation expert, which argued that the expert “failed to produce any proof of the methodology supporting the opinions that are being offered that [the medication] does not generally cause [the injury at issue]” (emphasis supplied). The common denominator in these arguments is conflation of the scientific and legal burdens for proving causation. In both motions, plaintiffs challenged a defense expert by explicitly or implicitly claiming that the expert failed to meet an obligation to prove or disprove causation which, in reality, resides solely with the plaintiff.

    The burden-shifting challenges presented in these two motions illustrate a broader trend in plaintiffs’ use of Daubert motions to challenge defense experts. These motions (which I will call “false equivalence” motions) attack defense experts by falsely equating plaintiff and defense causation opinions, and suggesting that the defense failed to adhere to the methodology applicable to the plaintiff. Once recognized, and assuming the expert was prepared to deal with burden shifting questions in depostion, false equivalence motions seldom present a serious threat of exclusion. However, they threaten to derail serious challenges to plaintiff experts. By filing these motions, plaintiffs confuse the scientific and legal standards and methodologies at issue, with the ultimate goal of causing the judge to write off a morass of confusing and conflicting claims about proper methodology as a mere “battle of experts.” Defense of the false equivalence motion is, therefore, important both for protection of the defense expert and preservation of legitimate challenges against plaintiff experts.

    Start With an Opinion Based on the Scientific Method


    At the core of most false equivalence motions is an implicit suggestion that the methodology and quantum of proof required to establish causation, or to refute it, are one and the same. But asserting and refuting causation are fundamentally different because “scientific methodology is based on generating hypotheses and testing them to see if they can be falsified.” Daubert v. Merrel Dow Pharm., 509 U.S. 579, 593 (1993) (citation omitted). As the United States District of Western Pennsylvania has explained, “falsify[ing] a hypothesis” in a toxic tort case requires proof that the “‘null hypothesis’—that [a substance] has no effect on the risk [in question]—is false, i.e., that [the substance] significantly increases the risk . . .” Soldo v. Sandoz Pharmaceuticals Corp., 244 F.Supp.2d 434, 457 (W.D. Pa. 2003). Thus, in the most technical terms, a plaintiff causation opinion is an opinion that the null hypothesis has been falsified, and a defense causation opinion is an opinion that the null hypothesis has not been falsified.

    In plainer terms, the plaintiff expert opines “substance X causes effect Y,” while the defense expert opines “it has not been established that substance X causes effect Y.” The defense expert usually does not opine that “substance X does not cause effect Y,” because epidemiology generally cannot establish the absence of causation. For these reasons, the plaintiff’s opinion demands proof of causation, while the defense expert’s opinion may simply be that proof is lacking.

    Prepare the Expert to Respond to Distortions and Reformulations

    The plaintiff’s first step in establishing false equivalence usually is a reformulation of the defense expert’s defensible opinion that “causation has not been established” into an opinion that a substance “does not cause” an effect. By this reformulation, the plaintiff erects a straw man that is far easier to topple; the defense expert now bears the burden of proving the absence of causation through epidemiological evidence. In the vast majority of cases, this amounts to an impossible burden.

    Having set the bar impossibly high, the plaintiff then exploits the defense expert’s inability to reach it. At deposition, the plaintiff poses different formulations of questions that explicitly or implicitly alter the expert’s opinion, as well as the scientific method, by demanding proof of the absence of an effect. The expert may be asked, for example, whether she can “tell the Court and jury in this case that to an absolute certainty, [the substance does not cause the claimed injury],” or provide citations to studies proving that there is no causal relationship. Each of these questions is based on a deliberate distortion of the expert’s actual opinion that evidence of causation is lacking.

    Plaintiffs may, relatedly, suggest that the expert inconsistently applied statistical significance standards by requiring significant results to establish causation, while relying on non-significant results to support the conclusion that causation has not been established. This approach is consistent with the bedrock scientific principle of hypothesis testing: studies that do not reach statistical significance fail to falsify the null hypothesis. Nevertheless, plaintiff’s counsel posed the following absurd question to our causation expert at a recent deposition: “are you telling us that there have been studies that have reported statistically significant odds ratios showing no association. . .?” Here, the defense expert is once again saddled with an impossible burden, because there cannot be a “statistically significant odds ratio showing no association.” By definition, a statistically significant result is one that excludes “no association.” (See Ref. Man. Scientific Ev. (3d Ed.) at 621 (“Where a confidence interval contains a relative risk of 1.0, the results of the study are not statistically significant.”).)

    Defense against these tactics begins with careful determination of the precise opinion a defense causation expert can and should offer. Usually, this will be an opinion in the form “causation has not been established,” rather than the plaintiff’s preferred reformulation, “does not cause.” The expert must then be prepared for the numerous confusing ways in which plaintiff’s counsel will attempt to twist both the expert’s opinion and the scientific method to support a false equivalence argument. Most importantly, the expert needs to be prepared to clearly explain the scientific principle of hypothesis testing and her opinion’s adherence to that principle.

    Be Careful With Alternative Causes

    Plaintiffs also may raise arguments sounding in false equivalence in response to a defense expert’s opinions on alternative causation. Here, the plaintiff argues that the defense expert applied a different standard to determine that the substance at issue did not cause the plaintiff’s injury than she did in determining that an alternative substance or condition did cause the injury. The defendant must recognize, first, that there is a legitimate potential for inconsistency in this area. It may be tempting to ascribe causation to any potential alternative, even if the causal evidence supporting the alternative cannot readily be distinguished from the evidence for the substance being defended. This temptation must be resisted, however, because application of truly inconsistent standards is an unreliable methodology. See, e.g., Soldo, 244 F. Supp. 2d at 566 (excluding plaintiff experts who, inter alia, applied inconsistent causation standards to alternative causes).

    Yet the defendant still should consider the potential for the expert to offer defensible opinions on alternative causation which fall short of an opinion that the alternative more likely than not caused the plaintiff’s injury. For example, the defense expert may reliably opine that an alternative cause cannot be ruled out, or that the plaintiff expert did not adequately consider the alternative cause, even if she cannot definitively ascribe causation to the alternative.

    Remember Who Bears the Burden of Proof


    Plaintiffs may nevertheless challenge any opinion stated by a defense expert that does not ascribe causation to a reasonable probability. This argument is based on a false equivalence between the required quantum of proof to support a plaintiff or a defense causation opinion. It is plainly the plaintiff’s burden to establish causation, and courts have repeatedly recognized the propriety of defense opinions critiquing or undermining the plaintiff expert’s opinion, even where the defense expert cannot offer a more-probable-than-not conclusion.

    The Eighth Circuit, for example, rejected a challenge to a defense expert’s opinion that “there were at least four more likely scenarios for how” an injury occurred, on the grounds that the expert did not “offer an opinion as to which possibility was, to a reasonable degree of medical certainty, more likely.” Allen v. Brown Clinic, PLLP, 531 F. 3d 568, 573 (8th Cir. 2008). The court rejected this argument, noting that it sought “to preclude the testimony of defendants’ expert by shifting the burden of proof,” and that the defendant “need not prove another cause.” Id. (internal quotation omitted). The Eastern District of Pennsylvania, similarly, rejected a challenge to a defense expert’s methodology where the expert had not “reached an opinion, with a degree of medical certainty, on precisely what caused plaintiff’s injuries.” Wolfe v. McNeil-PPC, Inc., Civ. Action No. 07-348, 2011 WL 1673805, *14 (E.D. Pa. May 4, 2011). The court acknowledged the plaintiff’s obligation to offer causation opinions to a reasonable probability, but then noted that “where defendant seeks to introduce evidence merely to cast doubt on the plaintiff’s theory of causation, the expert need not definitively rule out the plaintiff’s theory for his testimony to be admitted.” Id.

    Careful articulation of the pertinent burden of proof is the final step in opposing plaintiffs’ false-equivalence arguments. Each of the plaintiff strategies discussed above is based on an inversion of that burden, because each of the strategies implicitly suggests that the defense expert bears the burden of disproving causation. Accordingly, in addition to correcting distortions of the expert’s opinion, and of the scientific principles at issue, the opposition to a false equivalence motion usually elucidates and refutes plaintiff’s attempt to shift the burden of proof to the defense.