Manning the Daubert gate: a defense primer in response to Milward v. Acuity Specialty Products.

• Author: Lasker, Eric

ON JANUARY 9, 2012, the United States Supreme Court denied certiorari in Milward v. Acuity Specialty Prods. Group, Inc. (1) and, in so doing, let stand a First Circuit holding that a plaintiff expert's medical causation opinion resting solely on a self-proclaimed "weight of the evidence" analysis satisfied the Daubert requirements of scientific reliability and relevance. Even prior to the Supreme Court's certiorari decision, the plaintiff bar and its allies heralded Milward as holding out the "promise of reshaping toxic tort causation law," (2) and the newly-issued Restatement (Third) of Torts had labeled Milward "[o]ne of the most significant toxic tort causation cases in recent memory." (3) With Milward now final, defendants in toxic tort, pharmaceutical, and other science-based litigation can anticipate confronting Milward in response to any future Daubert challenge to plaintiff causation experts.

In the author's opinion, Milward was wrongly decided and flies in the face of the Supreme Court's holdings in Daubert v. Merrell Dow Pharms., Inc. (4) and General Elec. Co. v. Joiner. (5) However, any discussion of the Milward opinion also cannot be divorced from the factual pattern from which it arose. In Milward, the plaintiffs' expert was opining on causation with respect to a very rare form of cancer, and each side acknowledged there currently was--and perhaps could only ever be--limited scientific evidence on causation. While Daubert clearly cautions that "[l]aw lags science" (6) and that "the balance ... struck by the Rules of Evidence" requires exclusion even of potentially "authentic insights and innovations," (7) Daubert decisions involving such potentially unprovable scientific issues have repeatedly proved the adage that "bad facts make bad law." The Milward should be properly understood in this limiting context.

Defendants must, of course, continue to hold courts to their proper gate-keeping responsibilities under Daubert even in cases involving novel causation issues. By definition, however, the type of claimed-unprovable causation question at issue in Milward is more the exception than the rule. In most cases, including those involving an FDA- or EPA-regulated product, plaintiff experts will be offering causation opinions regarding relatively more common diseases and potential exposures as to which there is an established body of scientific evidence. Milward has little to say about these cases. Indeed, based upon the author's experience in prior litigation handled by his firm, Milward may not be predictive even of how the First Circuit will address expert causation testimony in future cases.

This article will provide a defense primer on how to respond to plaintiffs' use of Milward, both in cases involving novel causation issues and in the more common situation in which the plaintiff's expert is faced with an existing body of scientific knowledge. Section I reviews the Milward opinion, both at the district court and the First Circuit. Section II focuses on the numerous legal flaws in Milward, which should limit its applicability in other federal circuits that properly apply the Daubert gatekeeping standards. Section III addresses the narrow factual setting in which Milward arose, which also should limit its applicability in future cases, even within the First Circuit. Finally, Section IV recounts how the author's law firm addressed and negated a similarly flawed Daubert ruling from the Eighth Circuit Court of Appeals in successfully defending a Daubert victory in a pharmaceutical products liability action in the same Court less than a year later.

1. The Flawed Milward Ruling

   Milward is a products liability case in which the plaintiff alleges that workplace exposures to benzene-containing products caused a rare type of acute myeloid leukemia (AML) called acute promyelocytic leukemia (APL). As the defendants' own experts acknowledged before the district court, there is no dispute that scientific and medical evidence supports a causal link between benzene and the development of AML. (8) However, as the defendants' experts also explained, "clear differences exist among AML subtypes that may make inappropriate a broad extrapolation from AML generally to APL specifically." (9) Plaintiffs' expert acknowledged that there are no epidemiological studies demonstrating a causal link between benzene and APL, but he argued that the rarity of APL made it very difficult to perform such an epidemiological study.(10) Instead, plaintiffs' expert argued that causation could be inferred from an analogy between APL and other types of AML known to be associated with benzene, experimental research on AML etiology, and toxicological studies of chromosomal impacts of benzene exposure through the inhibition of an enzyme called topoisom erase II (topo II). While none of these pieces of evidence provided reliable support of causation in and of itself, plaintiffs' expert opined that the "weight of the evidence" demonstrated that benzene could cause APL. (11)

   After carefully reviewing each of the plaintiff experts' different lines of scientific evidence, the district court excluded the expert's causation opinion under Daubert. The district court explained that the plaintiffs' expert's opinion "that because benzene metabolites inhibit topo II and because some classes of topo II inhibitors appear to have a causal relationship to APL, therefore benzene has a causal relationship to APL is at best a theory and at worst an error." (12) The district court held that while the plaintiffs' expert causation hypotheses were "'plausible,' they remain hypotheses, the validity of which has not been reliably established. As such, they are not admissible as 'scientific knowledge' under Rule 702." (13) The First Circuit reversed. The First Circuit did not directly dispute any of the district court's conclusions with respect to the individual lines of causation evidence.

   The Court held, however, that the district court "erred in reasoning that because no one line of evidence supported a reliable inference of causation, an inference of causation based on the totality of the evidence was unreliable." (14) The district court's error--according to the First Circuit--

   derived from a mistake in its understanding of the weight of the evidence methodology employed by [plaintiffs' expert]. The court treated the separate evidentiary components of [the expert's] analysis atomistically, as though his ultimate opinion was independently supported by each.... [But in the expert's] weight of the evidence approach, no body of evidence was itself treated as justifying an inference of causation. Rather, each body of evidence was treated as grounds for the subsidiary conclusion that it would, if combined with other evidence, support a causal inference. (15) The First Circuit explained that the plaintiffs' expert's "weight of the evidence" approach employed the methodology of adductive inference or inference to the best explanation, whereby rather than drawing conclusions through logical inferences from known propositions or from a range of known particulars, conclusions "are drawn about a particular proposition or event by a process of eliminating all other possible conclusions to arrive at the most likely one, the one that best explains the available data." (16) The Court further explained that "[b]ecause no scientific methodology exists for this process ... reasonable scientists may come to different judgments about whether such an inference is appropriate." (17)

   In reversing the district court opinion, the First Circuit held that "[n]o serious argument can be made that the weight of the evidence approach is inherently unreliable." (18) The Court allowed, however, that the "admissibility [of weight of the evidence testimony] must turn on the particular facts of the case." (19) One of the key "particular facts" in Milward was the rarity of the disease at issue. (20) This fact was central in the First Circuit's discussion of the lack of...