An expert witness is not supposed to pick a desired result and then reverse engineer inputs and methods that reach that result. As the Ninth Circuit observed 30 years ago, “[c]oming to a firm conclusion first and then doing research to support it is the antithesis of [the scientific] method.” Claar v. Burlington Northern R.R. Co., 29 F.3d 499, 502-03 (9th Cir. 1994). A recent opinion from the Southern District of Illinois offers a fine example of an expert with a results-driven approach and a court that called him out on it.
In re Paraquat Products Liability Litigation, 2024 WL 1659687 (S.D. Ill. Apr. 17, 2024), arises from a multidistrict litigation (“MDL”) in which the plaintiffs claim to have developed Parkinson’s disease as a result of exposure to an herbicide, paraquat. Four plaintiffs whose cases had been chosen for the MDL’s first trials offered a statistician (the parties disputed whether he also qualified as an epidemiologist) as their sole expert to establish general causation. He had a difficult task, as no peer-reviewed literature established a link between paraquat exposure and Parkinson’s disease. Indeed, when the court asked the plaintiffs to identify such literature, the plaintiffs could cite only a single opinion article. That article had been shared with another of the plaintiffs’ experts before it was published, leading the court to conclude in deciding a prior discovery dispute that there was reason to investigate “whether counsel for the MDL plaintiffs, their experts, or other third parties may have influenced the contents of the article for the benefit of one side in the MDL.” 2023 WL 8372819 (S.D. Ill. Dec. 4, 2023).