In a differential etiology, experts need not rule out all possible causes

ABSTRACT: Experts are not required to rule out all possible causes when performing the differential etiology analysis if the experts have properly ruled in the alleged cause.

In Johnson v. Mead Johnson & Co., LLC (No. 13-1685), 2014 U.S.App. LEXIS 10541 (8^th Cir. June 6, 2014), the court reaffirmed the applicability of the Daubert standard to both the “ruling in” and “ruling out” process of differential etiology, the process by which an expert determines the cause of an injury. In passing, the Eighth Circuit noted that "a differential diagnosis is a tested methodology, has been subjected to peer review/publication, does not frequently lead to incorrect results, and is generally accepted in the medical community."  Thus, the differential etiology and diagnosis in general pass muster under the four considerations identified in Daubert:

(1) whether the scientific technique can be or has been tested; (2) whether the theory or technique has been subjected to peer review and/or publication; (3) the known rate of error for the technique or theory and the applicable standards for operation; and (4) whether the technique is generally accepted.

The key inquiry in admissibility is whether the experts’ methodology is reliable enough to assist the trier of fact. In this case, all of the experts in the case agreed the experts properly “ruled in” the product at issue as a likely cause of the injury based on published studies by the World Health Organization and the Centers for Disease Control and Prevention. 

The District Court found that two proffered experts did not “efficaciously rule out” other plausible sources of injury. However, the Eighth Circuit held that experts “are not required to rule out all possible causes when performing the differential etiology analysis.” Instead, such considerations “go the weight to be given the testimony by the fact finder, not its admissibility.” Thus, the Eighth Circuit admitted all of the expert testimony and reversed the district court’s granting of summary judgment. The full opinion may be found here.