The Eleventh Circuit recently  affirmed a judgment for defendant Evenflo Co. in a suit by a plaintiff who had alleged that the car seat manufacturer was responsible for her son’s autism. Hendrix v. Evenflo Co., 2010 WL 2490760 (11th Cir., 6/22/10).

Plaintiff alleged that her son sustained traumatic brain injuries when a child restraint system manufactured by Evenflo allegedly malfunctioned during a minor traffic accident. Hendrix further alleged that those brain injuries caused the son to develop autism spectrum disorder (“ASD”). The district court excluded testimony from two of Hendrix’s expert witnesses that the accident caused the ASD, concluding that the methods used by Hendrix’s experts were not sufficiently reliable under Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993). See Hendrix v. Evenflo Co., Inc., 255 F.R.D. 568 (N.D.Fla. 2009). The lower court then granted partial summary judgment to Evenflo on Hendrix’s ASD claim, determining that without the excluded testimony there was no reliable evidence to support Hendrix’s theory that the accident caused the ASD. Hendrix voluntarily dismissed, with prejudice, her remaining damages claims and filed a notice of appeal.

Hendrix’s experts relied primarily on the controversial differential etiology method to link the child’s traumatic brain injury to his ASD diagnosis. Differential etiology, said the court, is a medical process of elimination whereby the possible causes of a condition are considered and ruled out one-by-one, leaving only one cause remaining. It is a questionable extension of the method by which doctors diagnose a disease into the area of what caused the disease.

The Eleventh Circuit has previously held that, when applied under certain circumstances that it thinks will ensure reliability, the differential etiology method can provide a valid basis for medical causation opinions. The reliability of the method must be judged by considering the reasonableness of applying the differential etiology approach to the facts of this case and the validity of the experts’ particular method of analyzing the data and drawing conclusions therefrom. According to the court, a reliable differential etiology analysis is performed in two steps. First, the expert must compile a comprehensive list of hypotheses that might explain the set of salient clinical findings under consideration; the issue at this point in the process is which of the competing causes are generally capable of causing the patient’s symptoms. See Clausen v. M/V New Carissa, 339 F.3d 1049, 1057-58 (9th Cir.2003). Second, the expert must eliminate all causes but one.

With regard to the first step, the district court must ensure that, for each possible cause the expert “rules in” at the first stage of the analysis, the expert’s opinion on general causation is derived from scientifically valid methodology.  Hollander v. Sandoz Pharm. Corp., 289 F.3d 1193, 1211 (10th Cir.2002); Siharath v. Sandoz Pharms. Corp., 131 F.Supp.2d 1347, 1362-63 (N.D.Ga.2001). This is because a fundamental assumption underlying differential etiology is that the final, suspected cause must actually be capable of causing the injury. Thus, here, the experts’ purported use of the differential etiology method will not overcome a fundamental failure to lay the scientific groundwork for the theory that traumatic brain injury can, in general, cause autism.

The Eleventh Circuit has distinguished cases in which the medical community generally recognizes that a certain chemical or product can cause the injury the plaintiff alleges from those in which the medical community has not reached such a consensus. In the second category of cases, the district court must apply the Daubert analysis not only to the expert’s methodology for figuring out whether the agent caused the plaintiff’s specific injury, but also to the question of whether the drug or chemical or product can, in general, cause the harm plaintiff alleges. Thus, the district court must assess the reliability of the expert’s opinion on general, as well as specific, causation.  In this regard, the court (like most) rejects the “post hoc ergo propter hoc fallacy” which assumes causality from temporal sequence; a mere temporal relationship between an event and a patient’s disease or symptoms does not allow an expert to place that event on a list of possible causes of the disease or symptoms. Case studies and clinical experience, used alone and not merely to bolster other evidence, are also insufficient to show general causation.

Here, none of the medical textbooks and epidemiological studies submitted by the expert came close to providing useful evidence of a definitive causal link between traumatic head injuries and autistic disorders, and none provided even marginal support for plaintiff’s theory of a relationship between abnormal cerebral spinal fluid pressure and problems with cerebellum pressure, leading to autism. For example, the text chapter listing the known etiological factors involved in ASD does not mention acquired trauma in the perinatal brain.

Plaintiff also attempted to sidestep the deficiencies in the medical literature by focusing on the expert’s experience and training. Merely demonstrating that an expert has experience, however, does not automatically render every opinion and statement by that expert reliable. The witness must explain how that experience leads to the conclusion reached, why that experience is a sufficient basis for the opinion, and how that experience is reliably applied to the facts. The trial court’s gatekeeping function requires more than simply “taking the expert’s word for it.”

Judgment for defendant affirmed.