Opinion ID: 212992
Heading Depth: 2
Heading Rank: 1

Heading: The Reliability of the Weight of the Evidence Methodology

Text: Dr. Smith's opinion was based on a weight of the evidence methodology in which he followed the guidelines articulated by world-renowned epidemiologist Sir Arthur Bradford Hill in his seminal methodological article on inferences of causality. See Arthur Bradford Hill, The Environment and Disease: Association or Causation?, 58 Proc. Royal Soc'y Med. 295 (1965). Hill's article explains that one should not conclude that an observed association between a disease and a feature of the environment (e.g., a chemical) is causal without first considering a variety of viewpoints on the issue. These viewpoints include: the strength or frequency of the association; the consistency of the association in varied circumstances; the specificity of the association; the temporal relationship between the disease and the posited cause; the dose response curve between them; the biological plausibility of the causal explanation given existing scientific knowledge; the coherence of the explanation with generally known facts about the disease; the experimental data that relates to it; and the existence of analogous causal relationships. See id. at 295-99. [5] Although Hill identified nine viewpoints, it is generally agreed that this list is not exhaustive and that no one type of evidence must be present before causality may be inferred. For example, when a group from the National Cancer Institute was asked to rank the different types of evidence, it concluded that [t]here should be no such hierarchy. [6] Michele Carbon et al., Modern Criteria to Establish Human Cancer Etiology, 64 Cancer Res. 5518, 5522 (2004); see also Sheldon Krimsky, The Weight of Scientific Evidence in Policy and Law, 95 Am. J. Pub. Health S129, S130 (2005). This weight of the evidence approach to making causal determinations involves a mode of logical reasoning often described as inference to the best explanation, in which the conclusion is not guaranteed by the premises. [7] See Bitler v. A.O. Smith Corp., 391 F.3d 1114, 1124 n. 5 (10th Cir. 2004). As explained by plaintiffs' expert on methodology Dr. Cranor, Distinguished Professor of Philosophy at the University of California, Riverside, inference to the best explanation can be thought of as involving six general steps, some of which may be implicit. The scientist must (1) identify an association between an exposure and a disease, (2) consider a range of plausible explanations for the association, (3) rank the rival explanations according to their plausibility, (4) seek additional evidence to separate the more plausible from the less plausible explanations, (5) consider all of the relevant available evidence, and (6) integrate the evidence using professional judgment to come to a conclusion about the best explanation. In this mode of reasoning, the use of scientific judgment is necessary. No algorithm exists for applying the Hill guidelines to determine whether an association truly reflects a causal relationship or is spurious. Restatement § 28 cmt. c(3). Because [n]o scientific methodology exists for this process . . . reasonable scientists may come to different judgments about whether such an inference is appropriate. Id. § 28 reporters' note cmt. c(4). The fact that the role of judgment in the weight of the evidence approach is more readily apparent than it is in other methodologies does not mean that the approach is any less scientific. No matter what methodology is used, an evaluation of data and scientific evidence to determine whether an inference of causation is appropriate requires judgment and interpretation. Id. § 28 cmt. c(1). [8] The use of judgment in the weight of the evidence methodology is similar to that in differential diagnosis, see Cruz v. Bridgestone/Firestone N. Am. Tire, LLC, 388 Fed.Appx. 803, 806-07 (10th Cir.2010) (explaining that differential analysis in general is best characterized as a process of reasoning to the best explanation), which we have repeatedly found to be a reliable method of medical diagnosis, see Granfield v. CSX Transp., Inc., 597 F.3d 474, 486 (1st Cir.2010); Dalkon Shield, 156 F.3d at 253. Defendants argue that regardless of its level of acceptance in the scientific community, a pure `weight of the evidence' approach like that utilized by Dr. Smith . . . is hardly the type of reliable scientific evidence contemplated by Daubert. [9] No serious argument can be made that the weight of the evidence approach is inherently unreliable. Rather, admissibility must turn on the particular facts of the case. See, e.g., Cruz, 388 Fed.Appx. at 807 (explaining that expert testimony based on inference to the best explanation may be admissible, but that there was no error in the district court's finding that the expert's specific theory did not have sufficient scientific support). Here, the question is whether Dr. Smith, in reaching his opinion, applied the methodology with the same level of intellectual rigor that he uses in his scientific practice. Kumho Tire, 526 U.S. at 152, 119 S.Ct. 1167.