On Aug. 26, 2015, the Seventh Circuit affirmed the exclusion of three expert witnesses who proffered opinions based on differential etiology as unreliable, but noted that “there may be a case where a rigorous differential etiology is sufficient to help prove, if not prove altogether both general and specific causation.” C.W. v. Textron, Inc., No. 14-3448 (7th Cir. Aug. 25, 2015). In C.W., the plaintiffs alleged that Textron, which operated a fastener manufacturing plant, released vinyl chloride, contaminating the groundwater in neighboring residential wells, including that of the plaintiffs. Plaintiffs brought claims against Textron for negligence, negligence per se, and negligent infliction of emotional distress, alleging that their two young children were exposed to the vinyl chloride, which caused illness and substantially increased their risk of cancer and other illnesses.

To support their claims, the plaintiffs proffered the testimony of three expert witnesses who opined that the children’s exposure to vinyl chloride caused illnesses and increased their risk of cancer. The United States District Court for the Northern District of Indiana, applying Daubert, excluded the testimony of the three experts, which relied on differential etiology, as not sufficiently reliable because the experts had failed to connect the dots between the available scientific studies and the illnesses endured by the children. In excluding the experts, the court found that their analysis required too great of an analytical gap between the scientific studies cited by the experts and their opinions that exposure to vinyl chloride at the doses and duration present could cause the problems that plaintiffs claim to have experienced or are likely to experience.

The Seventh Circuit agreed with the district court that, in this case, the three proffered experts did not use reliable methodology to develop their differential etiology opinions. Recognizing the unavailability of scientific studies that directly address the effects of vinyl chloride in children, the court noted that “there is a scientific end-around to make up for this dearth in literature. Scientists have developed computer-based models to extrapolate from animal data to human subjects, and from high doses to lower doses.” Id. (citing Bernard D. Goldstein & Mary Sue Henifin, Reference Guide on Toxicology in Federal Manual of Scientific Evidence 646 (3rd ed. 2011).

Although the Seventh Circuit affirmed the district court’s exclusion of the three experts, however, it disagreed with the district court’s conclusion that differential etiology is admissible only as to specific causation and “cannot be used to support general causation.” The court expressly adopted the approach of the Second Circuit to find that differential etiology, if found to be sufficiently rigorous and reliable, may be admissible to prove both general and specific causation.  Id. (citing Ruggiero v. Warner-Lambert Co., 424 F. 3d 249, 254 (2d Cir. 2005).