The Seventh Circuit recently held that a lower court was correct to preclude a proposed causation expert from testifying for the plaintiffs in a suit relating to a plaintiff''s alleged exposure to chlorine gas at an Indiana amusement park.  See  Kent Higgins, et al. v. Koch Development Corp., No. 14-2207 (7th Cir. 7/20/15).

At the park, plaintiff allegedly inhaled an unspecified amount of chemical fumes that lingered in the air near malfunctioning equipment.  Complaining of chest tightness, burning eyes, shortness of breath, and nausea, Higgins visited the emergency room later that day, where he was diagnosed with “mild chemical exposure” and discharged with instructions to follow up with his primary care physician. More than a year later he was diagnosed with reactive airways dysfunction syndrome (“RADS”) and chronic asthma. 

This treater, Dr. Haacke, was offered as an expert, and when challenged, plaintiff's argument appeared to be that she was qualified merely because she was a board certified pulmonologist. Although a doctor may have “experience diagnosing and treating asthma … that does not make him qualified to ‘assess its genesis.’” Cunningham v. Masterwear, Inc., 2007 WL 1164832, at *10 (S.D. Ind. Apr. 19, 2007). Plaintiff offered no evidence that Dr. Haacke had ever treated another patient for chlorine gas exposure or had any training in toxicology. Nor could plaintiff establish that Dr. Haacke employed a reliable methodology in forming her causation opinion (even assuming she was qualified to do so). The expert essentially diagnosed Higgins after listening to his own description of his symptoms and the events at the park—some fourteen months after the fact—and after looking at the results (though not the underlying data) of the pulmonary function study conducted by another doctor the year before.

The record was silent on whether Dr. Haacke considered other possible causes of Higgins’s ailments and, if so, how and why she ruled them out. That is problematic, because plaintiff argued the doctor was employing “differential diagnosis."  A "differential diagnosis” actually refers to a method of diagnosing an ailment, not determining its cause. See Myers, 629 F.3d at 644. Some courts have recognized a form of  "differential etiology,” as a causation‐determining methodology. Even then, to be validly conducted, an expert must systematically “rule in” and “rule out” potential causes in arriving at her ultimate conclusion. There was no showing that this was done.

The expertsʹ work is admissible only to the extent it is reasoned, uses the methods of the discipline, and is founded on data.  Lang v. Kohl’s Food Stores, Inc., 217 F.3d 919, 924 (7th Cir. 2000). Accordingly, it was within the district court’s discretion to deem Dr. Haacke unqualified to proffer this expert testimony.