How not to do a differential diagnosis — UPDATED

The plaintiffs in Sims v. Kia Motors brought products liability claims about the design of a fuel tank. Their main engineering expert “employed a ‘differential diagnosis approach, a scientific technique that essentially involves the process of elimination.” While a potentially reliable technique, the Fifth Circuit noted that it “has cautioned that “the results of a differential diagnosis are far from reliable per se..’ . . . “[M]erely “ruling out” other possible explanations is not enough to establish reliability; experts must also have some scientific basis for ‘ruling in’ the phenomenon they allege.” Here, where “the record does not reflect any reliable facts or data ‘ruling in'” the expert’s theory about how the fuel tank behaved in the accident, “the district court did not abuse its discretion in excluding it.” No. 15-10636 (revised Oct. 11, 2016).