In a Minnesota products liability suit, expert testimony based on a differential etiological analysis is scientifically valid, reasonably applied and sufficiently reliable to be admitted under Daubert v. Merrell Dow Pharm., Inc., 509 U.S. 579 (1993) and Fed. R. Evid. 702. In evaluating the differential etiology method in the case at hand, the Eighth Circuit Court of Appeals explained that experts are not required to rule out all possible causes because a differential expert opinion can be reliable with less than full information.
In Johnson v. Mead Johnson, LLC, — F.3d —, 2014 WL 2535324 (8th Cir. 2014), Plaintiff, in his capacity as guardian ad litem, brought suit against Defendant asserting that H.T.P., a minor, contracted a bacterial infection and subsequently sustained brain injuries after ingesting Defendant’s powdered infant formula contaminated with Cronobacter sakazakii. Id. at *2.
The United States District Court for the District of Minnesota agreed that Defendant’s powdered infant formula is a scientifically plausible cause of H.T.P.’s injuries, but excluded Plaintiff’s expert testimony on specific causation. Id. The District Court concluded that Plaintiff’s experts failed to rule out possible alternative causes of H.T.P.’s infection in their differential etiological analysis. Id. The District Court granted Defendants’ summary judgment motion holding that Plaintiff cannot prove Defendant’s powdered infant formula caused H.T.P.’s injuries. Id.
Plaintiff argued on appeal that nothing in Fed. R. Evid. 702, Daubert, or its progeny required an expert to resolve an ultimate issue of fact to a scientific absolute to be admissible. Plaintiff further argued that in conducting the differential analysis, Plaintiff’s experts considered sources other than powdered infant formula as sources that could have given rise to the minor’s C. sak infection and explained why they rejected those alternatives as the likely cause of the infection. Plaintiff further argued that his experts’ testimony should be presented to the jury and tested in the adversary process, and that it was an abuse of discretion to exclude such testimony.
Defendant argued the District Court did not abuse its discretion when Plaintiff’s experts lacked sufficient data, did not employ a reasonable methodology, and did not reliably apply the differential etiology analysis. Defendant further argued that the District Court properly acted as a referee of the scientific methods and data relied on by Plaintiff’s experts and excluded such testimony.
The Court of Appeals reversed and held the District Court abused its discretion in excluding the experts’ testimony. Johnson, 2014 WL 2535324, at *6. In so ruling, the Court emphasized that Daubert and Rule 702 liberalized the admission of expert testimony and explained that “[a]s long as the expert’s scientific testimony rests upon ‘good grounds, based on what is known’ it should be tested by the adversary process with competing expert testimony and cross-examination, rather than excluded by the court at the outset.” Id. at *4 (citing Daubert, 509 U.S. at 590, 596). In reaching its holding, the Court focused its attention on the third factor of the Fed. R. Evid. 702 test for admissibility: whether the evidence is trustworthy enough to assist the trier of fact. The Court inquired whether the differential etiological method used by Plaintiff’s experts was sufficiently reliable to assist the trier of fact.
In a differential etiological method, an expert will first “rule in” the scientifically plausible causes and then “rule out” the least plausible causes. This methodology was previously accepted under the Daubert standard. See Johnson, 2014 WL 2535324, at *4 (citing Turner v. Iowa Fire Equip. Co., 229 F.3d 1202, 1208 (8th Cir. 2000)(“agreeing with other circuits who have held 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.’”)
In evaluating the differential etiology method in the case at hand, the Court of Appeals explained that experts are not required to rule out all possible causes because a differential expert opinion can be reliable “even with less than full information.” 2014 WL 2535324, at *4 (citing Lauzon, 270 F.3d at 693; In re Prempro Prods. Liab. Litig., 586 F.3d 547, 566-67 (8th Cir. 2009); In re Paoli v. R.R. Yard PCB Litig., 35 F.3d 717, 759 (3d Cir. 1994)). As a result, the Court of Appeals concluded the specific causation opinions offered by Plaintiff’s experts “were scientifically valid, could properly be applied to the facts of [the] case, and, therefore, [were] reliable enough to assist the trier of fact.” Johnson, 2014 WL 2535324, at *6. The Court of Appeals stated that Plaintiff was entitled to proceed to a jury on the issue of specific causation of H.T.P.’s C. sak infection and reversed the District Court’s order.