Opinion ID: 149189
Heading Depth: 2
Heading Rank: 2

Heading: Exclusion of Expert Testimony on Causal Link Between Traumatic Brain Injury and ASD

Text: Hendrix seeks to admit expert testimony that the traumatic brain injury G.P. sustained in the accident caused his ASD. Because this is a diversity case, we apply Florida's substantive law regarding a plaintiff's burden of proof on causation. McLeod v. Am. Motors Corp., 723 F.2d 830, 832 (11th Cir.1984). Under Florida law, Hendrix may recover damages upon showing that the trauma was a substantial factor causing G.P.'s ASD. Gross v. Lyons, 763 So.2d 276, 279 (Fla.2000); Hart v. Stern, 824 So.2d 927, 929-30 (Fla. 5th DCA 2002). A purported cause is a substantial factor if it operates in combination with another cause, such as the negligent act of another or the plaintiff's pre-existing physical condition, to cause an injury. Gross, 763 So.2d at 279; Hart, 824 So.2d at 929-30. Although the standards for finding causation are governed by Florida law, we apply federal law to determine whether the expert testimony proffered to prove causation is sufficiently reliable to submit it to the jury. Flury v. Daimler Chrysler Corp., 427 F.3d 939, 944 (11th Cir.2005) (noting that in diversity cases, the Federal Rules of Evidence govern the admissibility of evidence in federal court). The Federal Rules of Evidence provide: If scientific ... knowledge will assist the trier of fact to understand the evidence or to determine a fact in issue, a witness qualified as an expert by knowledge, skill, experience, training, or education, may testify thereto in the form of an opinion or otherwise, if (1) the testimony is based upon sufficient facts or data, (2) the testimony is the product of reliable principles and methods, and (3) the witness has applied the principles and methods reliably to the facts of the case. Fed.R.Evid. 702. Unlike an ordinary witness... an expert is permitted wide latitude to offer opinions, including those that are not based on firsthand knowledge or observation. Daubert, 509 U.S. at 592, 113 S.Ct. at 2796. [T]his relaxation of the usual requirement of firsthand knowledge... is premised on an assumption that the expert's opinion will have a reliable basis in the knowledge and experience of his discipline. Id. A trial court assessing the reliability of an expert's evidence must therefore perform a gatekeeping function by conducting a preliminary assessment of whether the reasoning or methodology underlying the testimony is scientifically valid and of whether that reasoning or methodology properly can be applied to the facts in issue. Id. at 592-93, 113 S.Ct. at 2796. We have offered district courts the following general guidance in determining whether to admit scientific evidence under Daubert: Given time, information, and resources, courts may only admit the state of science as it is. Courts are cautioned not to admit speculation, conjecture, or inference that cannot be supported by sound scientific principles. The courtroom is not the place for scientific guesswork, even of the inspired sort. Law lags science; it does not lead it. Rider v. Sandoz Pharms. Corp., 295 F.3d 1194, 1202 (11th Cir.2002) (quoting Rosen v. Ciba-Geigy Corp., 78 F.3d 316, 319 (7th Cir.1996)). This circuit requires trial courts acting as gatekeepers to engage in a rigorous three-part inquiry assessing whether: (1) the expert is qualified to testify competently regarding the matters he intends to address; (2) the methodology by which the expert reaches his conclusions is sufficiently reliable as determined by the sort of inquiry mandated in Daubert ; and (3) the testimony assists the trier of fact, through the application of scientific, technical, or specialized expertise, to understand the evidence or to determine a fact in issue. United States v. Frazier, 387 F.3d 1244, 1260. The proponent of the expert testimony bears the burden of showing, by a preponderance of the evidence, that the testimony satisfies each prong. See Boca Raton Cmty. Hosp., Inc. v. Tenet Health Care, 582 F.3d 1227, 1232 (11th Cir.2009). Here, the parties raise no issues regarding the first and third prongs. Therefore, our analysis will focus on whether the district court abused its discretion in excluding the expert testimony of Dr. Hoffman and Dr. Suhrbier upon finding that the testimony was not sufficiently reliable under Daubert. The Daubert Court described several factors trial judges may use to assess the reliability of proffered scientific testimony, including: (1) whether the theory or technique can be (and has been) tested, (2) whether the theory or technique has been subjected to peer review and publication, (3) in the case of a particular scientific technique, ... the known or potential rate of error, and (4) whether the theory or technique is generally accepted by the relevant scientific community. Daubert, 509 U.S. at 592-94, 113 S.Ct. at 2796-97; see also Rink, 400 F.3d at 1292 (discussing these factors in the context of assessing an expert's particular scientific technique). This list, however, is not exhaustive, and district courts have substantial discretion in deciding how to test an expert's reliability. Rink, 400 F.3d at 1292. In addition, the Supreme Court has noted that, in the context of this analysis, conclusions and methodology are not entirely distinct from one another. General Elec. Co. v. Joiner, 522 U.S. 136, 146, 118 S.Ct. 512, 519, 139 L.Ed.2d 508 (1997). Although experts commonly extrapolate from existing data ... nothing in either Daubert or the Federal Rules of Evidence requires a district court to admit opinion evidence that is connected to existing data only by the ipse dixit of the expert. Id. Rather, the trial court is free to conclude that there is simply too great an analytical gap between the data and the opinion proffered. Id. Hendrix's experts rely primarily on the differential etiology method [5] to link G.P.'s traumatic brain injury to his ASD diagnosis. Differential etiology 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. See supra n. 5. Hendrix argues that the experts' opinions were reliable because differential etiology is a well-recognized scientific method that has been accepted by many courts as a valid basis for expert testimony. See, e.g., Best v. Lowe's Home Centers, Inc., 563 F.3d 171, 178-84 (6th Cir.2009); McClain, 401 F.3d at 1252-53; Clausen v. M/V New Carissa, 339 F.3d 1049, 1057 (9th Cir. 2003). We have previously noted that, when applied under circumstances that ensure reliability, the differential etiology method can provide a valid basis for medical causation opinions. See McClain, 401 F.3d at 1252. Here, 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. See Kumho Tire, 526 U.S. at 153-54, 119 S.Ct. at 1177 ([T]he specific issue before the court was not the reasonableness in general of a tire expert's use of a visual and tactile inspection to determine whether overdeflection had caused the tire's tread to separate from its steel-belted carcass. Rather, it was the reasonableness of using such an approach, along with Carlson's particular method of analyzing the data thereby obtained, to draw a conclusion regarding the particular matter to which the expert testimony was directly relevant. ) (emphasis in original); see also Quiet Tech. DC-8 v. Hurel-Dubois UK Ltd., 326 F.3d 1333, 1343 (11th Cir.2003). 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. McClain, 401 F.3d at 1253 (quoting Clausen v. M/V NEW CARISSA, 339 F.3d 1049, 1057-58 (9th Cir. 2003)). Second, the expert must eliminate all causes but one. See McCullock v. H.B. Fuller Co., 61 F.3d 1038, 1044 (2d Cir. 1995). 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) (quoting 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. McClain, 401 F.3d at 1253. Thus, 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. See McClain, 401 F.3d at 1252 (This approach, however, will not usually overcome the fundamental failure of laying a scientific groundwork for the general toxicity of the drug and that it can cause the harm a plaintiff suffered.). Some specific principles arise in the context of establishing general causation in cases dealing with medical injuries. In McClain, we distinguished cases in which the medical community generally recognizes that a certain chemical can cause the injury the plaintiff alleges from those in which the medical community has not reached such a consensus. 401 F.3d at 1239. [6] We stated that 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 chemical caused the plaintiff's specific injury, but also to the question of whether the drug or chemical can, in general, cause the harm plaintiff alleges. Id. Thus, the district court must assess the reliability of the expert's opinion on general, as well as specific, causation. Id. Hendrix does not contend that the medical community generally recognizes traumatic brain injury as a cause of autism. Therefore, the district court was correct to apply the Daubert analysis to the question of whether traumatic brain injury can, in general, cause autism. [7] We afford the district court substantial discretion to decide how to test the reliability of the general causation evidence presented by Dr. Hoffman and Dr. Suhrbier. Rink, 400 F.3d at 1292. In reviewing the district court's reliability determination, we note that we have previously identified some of the scientifically valid methods for establishing general causation. For instance, we will admit expert opinions pursuant to Daubert that are supported by epidemiological studies, [8] provided the expert explains how the findings of those studies may be reliably connected to the facts of the particular case. Rider, 295 F.3d at 1198 (noting that, although they are not mandatory, epidemiological studies may be powerful evidence of causation); see also, Norris v. Baxter Healthcare Corp., 397 F.3d 878, 882 (10th Cir.2005) ([E]pidemiology is the best evidence of general causation in a toxic tort case.). An expert's opinion will likely also survive Daubert if the expert describes the physiological process, derived by the scientific method, by which a particular cause leads to the development of a given disease or syndrome. McClain, 401 F.3d at 1253 (The underlying predicates of any cause-and-effect medical testimony are that medical science understands the physiological process by which a particular disease or syndrome develops and knows what factors cause the process to occur.) (quoting Black v. Food Lion, Inc., 171 F.3d 308, 314 (5th Cir.1999)); see also Daubert, 509 U.S. at 590, 113 S.Ct. at 2795 (noting that in order to qualify as scientific knowledge for the purposes of Fed. R.Evid. 702, an inference or assertion must be derived by the scientific method). Courts have also identified other methods that, when used alone, are unable to provide scientifically valid proof of general causation. For instance, in McClain, we explained that the  post hoc ergo propter hoc fallacy assumes causality from temporal sequence.... It is called a fallacy because it makes an assumption based on the false inference that a temporal relationship proves a causal relationship. McClain, 401 F.3d at 1243. Thus, 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. See Rider, 295 F.3d at 1199 (Although a court may rely on anecdotal evidence such as case reports... courts must consider that case reports are merely accounts of medical events. They reflect only reported data, not scientific methodology.) (internal citation omitted); see also Norris, 397 F.3d at 887 (We cannot allow the jury to speculate based on an expert's opinion which relies only on clinical experience in the absence of showing a consistent, statistically significant association between breast implants and systemic disease.). In the second step of the differential etiology analysis, the expert must eliminate all causes but one. See McCullock, 61 F.3d at 1044. While the first step focuses on general causation, in the second step the expert applies the facts of the patient's case to the list created in the first step in order to form an opinion about the actual cause of the patient's symptoms, i.e., to determine specific causation. In Clausen, the Ninth Circuit stated that an expert must provide reasons for rejecting alternative hypotheses using scientific methods and procedures and the elimination of those hypotheses must be founded on more than subjective beliefs or unsupported speculation. 339 F.3d at 1058 (internal quotation omitted). Thus, [a] district court is justified in excluding evidence if an expert `utterly fails ... to offer an explanation for why the proffered alternative cause' was ruled out. Id. (quoting Cooper v. Smith & Nephew, Inc., 259 F.3d 194, 202 (4th Cir.2001)). With these principles in mind, we now review the district court's determination that the experts' testimony in this case was unreliable under Daubert.
The district court determined that Dr. Hoffman's testimony regarding ASD causation was insufficiently reliable under Daubert to warrant admission of that testimony at trial. The district court identified errors in Dr. Hoffman's differential etiology analysis at both the rule in and rule out steps. Specifically, the district court determined that Dr. Hoffman fail[ed] to show how, by `scientifically valid methodology,' traumatic brain injury could ever be a possible cause of autism in anyone. Hendrix, 255 F.R.D. at 598. The court also found that Dr. Hoffman failed to compile `a comprehensive list' of all possible causes of ASD and accordingly that by failing to include all of the causes currently theorized in the medical literature in his `comprehensive list' of the possible causes of ASD, Hoffman failed to `rule out' all possible causes but one. [9] Hendrix, 255 F.R.D. at 597-98. We agree with the district court that Dr. Hoffman failed to rule in traumatic brain injury as a possible cause of ASD. Because our holding in that regard is a sufficient ground upon which the district court ruling may be affirmed, we need not address the district court's decision that Dr. Hoffman failed to rule out other known or plausible causes of ASD. Dr. Hoffman's sole support for his theory that, in general, traumatic brain injury can cause ASD came from certain medical textbooks and epidemiological studies submitted by Dr. Hoffman. The district court carefully considered all of the materials cited by Dr. Hoffman and concluded that none of these works come close to providing useful evidence of a definitive [10] causal link between traumatic head injuries and autistic disorders, [11] and none provide even marginal support for Hoffman's theory of a relationship between abnormal [cerebral spinal fluid] pressure and problems with cerebellum pressure, leading to autism. Id. at 600-01. We have carefully and exhaustively reviewed the literature cited by Dr. Hoffman and conclude that the district court's conclusion with regard to each piece of literature was reasonable. We hold that the district court reasonably concluded that none of the literature supported the reliability of Dr. Hoffman's proffered physiological process, and that none of the literature supported Dr. Hoffman's opinion that a traumatic brain injury like GP's could have caused or contributed to the development of ASD. Thus, we conclude that the district court was reasonable in determining that the literature overall does not provide the necessary support for Dr. Hoffman's opinions to render those opinions admissible under Daubert. Rather than duplicating the district court's persuasive analysis of the literature provided by Dr. Hoffman, see Hendrix 255 F.R.D. at 600-03, we will focus on those pieces of literature emphasized by Hendrix on appeal. At oral argument, Hendrix's counsel stated that the most compelling literature discussing the physiological process by which traumatic brain injury could cause autism is a chapter in a textbook edited by Evenflo's medical expert Dr. Joel Morgan. See Gerry A. Stefanatos & Wilson Q. Joe, Autistic Disorder, in Textbook of Clinical Neuropsychology, 185-260 (Joel E. Morgan & Joseph H. Ricker, eds., 2008). We read this chapter carefully and failed to discern any suggestion that brain damage resulting from post-birth traumatic brain injury can cause autism spectrum disorders. We also saw no support for Dr. Hoffman's theory that abnormal cerebral spinal fluid pressure in the cerebellum could cause ASD. The chapter states that certain learning and memory patterns found in autistic individuals have been interpreted as reflection of cerebellar pathology, but also notes that studies have shown that frontal lobe and basal ganglia are also involved in learning a memory, and that [c]onsequently, these findings could not rule out an explanation in terms of a frontal-striatal dysfunction rather than anomalies of frontal-cerebellar circuits. Id. at 202. Further on in the chapter, the authors discuss the role of the cerebellum in ASD in general, and note that histological studies of the autistic brain have consistently implicated reduction of Purkinje cells of the cerebellum. Id. at 221. They do not, however, opine as to what might cause such a reduction of those cells. While these statements provide some support for the idea that the cerebellum is linked to autism in a very general sense, they offer no reliable support for Dr. Hoffman's theory that a traumatic brain injury like the one G.P. suffered could cause or contribute to the development of ASD. We found no mention at all in the chapter of Dr. Hoffman's proposed physiological process involving abnormal cerebral spinal fluid pressure leading to ASD. Notably, although the chapter catalogues the known etiological factors involved in ASD, the section titled Etiological considerations does not mention acquired trauma in the perinatal brain. Id. at 213-17. The section discusses genetic factors at length, and then goes on to list extrinsic factors such as: viruses; the presence of other neurological conditions, such as epilepsy; birthing complications; teratogenic substances, such as cocaine; and autoimmune factors. Id. The section fails to mention traumatic brain injury, and the authors qualify even the factors they do list by noting that studies directed to examining etiologic factors in [autism] have suffered from limitations due to small sample sizes, inadequate specification of diagnostic categories, and significant heterogeneity of the autistic population. Id. at 217. Hendrix's counsel also noted as particularly persuasive an article titled Late Neurologic and Cognitive Sequelae of Inflicted Traumatic Brain Injury in Infancy. Barlow et al., Late Neurologic and Cognitive Sequelae of Inflicted Traumatic Brain Injury in Infancy, 116 Pediatrics, Aug. 2005. The article describes a variety of neurologic impairments, including many of the impairments from which G.P. suffers, found in children with inflicted traumatic brain injury (e.g., shaken baby syndrome). Id. at e174. While Hendrix criticizes the district court for discounting the article based on the distinction between inflicted (non-accidental) and accidental traumatic brain injury, the article itself supports the notion that the two types of injuries are distinct. For instance, the article notes that mortality rates for infants with inflicted traumatic brain injury are greater than those for infants whose injuries were accidental. Id. at e174. The article also self-limits its findings by pointing out the small sample size, the need for further study, and that the study lacked a control group. Id. at e184. In fact, the authors mention that previous similar studies used children with an accidental traumatic brain injury as control subjects against which to compare those subjects with inflicted injuries. Id. Moreover, although one patient in the study developed autism spectrum disorder, the authors note that the ASD patient may have had significant exposure to alcohol in utero. Id. at e183. The district court identified these shortcomings and noted that significantly, nothing in the study purports to show or explain the physiological process by which brain injury produces autism. Hendrix, 255 F.R.D. at 601. The court therefore concluded that this study was insufficient to support Dr. Hoffman's assertion that the literature supports his theory of causation or even a general causal link between accidental traumatic brain injury and ASD. We cannot say that this determination was an abuse of discretion. We found the most direct statement supporting the theory that traumatic brain injury can cause ASD in a textbook submitted by Dr. Hoffman that was not brought to our attention on appeal. That textbook states: Considerable precedent for deleterious effects of various perinatal insults on organizational events is provided by studies with experimental animals. Initial studies of later cortical neuronal development in undamaged areas adjacent to ischemic cortical injury in human infants show dendritic aberrations that could contribute importantly to subsequent cognitive deficits and epilepsy. It is a clinical truism that some children affected by one or more perinatal insults may exhibit neurological sequalae that are more severe than might be predicted from the extent of injury recognized by the usual brain imaging or neuropathological techniques. Volpe, Human Brain Development in Neurology of the Newborn at 82. In other words, this textbook provides some support for the idea that even minor injuries sustained by newborn brains can result in more severe neurologic impairments than one would expect from the initial extent of the injury. The textbook does not, however, link such injuries to ASD, or provide any support for Dr. Hoffman's theory of ASD causation involving abnormal cerebral spinal fluid pressure. We are satisfied that the district court did not abuse its discretion in concluding, based on the literature Dr. Hoffman himself provided, that there is no reliable support for Dr. Hoffman's assertion that perinatal and neonatal intensive care follow-up literature does support the association between injury to the developing brain, including traumatic brain injury, and later occurrence of autism spectrum disorder. [12] Because Dr. Hoffman offers no other scientifically reliable basis for his opinion, his testimony is the type of speculation, conjecture, or inference that we have cautioned district courts not to admit. Rider, 295 F.3d at 1202. Hendrix attempts to sidestep the deficiencies in the medical literature by focusing on Dr. Hoffman's experience and training. Merely demonstrating that an expert has experience, however, does not automatically render every opinion and statement by that expert reliable. As an Advisory Committee Note on Federal Rule of Evidence 702 states: If the witness is relying solely or primarily on experience, then 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. Committee Notes on Rules2000 Amendment (quoting Daubert v. Merrell Dow Pharms., Inc., 43 F.3d 1311, 1319 (9th Cir.1995)). Taking the expert's word for it is precisely what Hendrix suggests the district court should have done in this case; however, we have previously recognized that `[n]othing in either Daubert or the Federal Rules of Evidence requires a district court to admit opinion evidence that is connected to existing data only by the ipse dixit of the expert.' See McClain, 401 F.3d at 1244 (quoting Joiner, 522 U.S. at 146, 118 S.Ct. at 519 (1997)). Dr. Hoffman has not provided a reliable basis, derived by the scientific method, for concluding that traumatic brain injury can cause ASD. We decline to conclude that the district court abused its discretion in failing to admit Dr. Hoffman's testimony based on his experience alone. Because the medical literature adduced by Hendrix supports neither Dr. Hoffman's theory of causation involving abnormal cerebral spinal fluid pressure nor his ultimate opinion that a traumatic brain injury like G.P.'s can cause autism, and because Dr. Hoffman offers no other scientifically reliable basis for his opinion, [13] we hold that the district court did not abuse its discretion in concluding that Hendrix failed to establish general causation to support Dr. Hoffman's opinion. That is, Hendrix has failed reliably to rule in traumatic brain injuries like G.P.'s as a plausible cause of autism. Because this is a sufficient basis on which to affirm the district court's ruling excluding Dr. Hoffman's testimony, we need not address the district court's decision that Dr. Hoffman also failed to rule out other possible causes. The district court held: Hoffman's claim that he ruled out genetics as a potential cause of [G.P.'s] ASD based on [G.P.'s] normal Fragile X tests ignores the possibility of other genetic conditions as a cause. Given the plethora of genetic theories for autism, ruling out Fragile X as a possible cause of [G.P.'s] ASD far from eliminates all genetic causes of his ASD, let alone the other multitude of factors that have been linked to autism or ASD. Hendrix, 255 F.R.D. at 598 (footnotes omitted). The medical literature indicates that there are a dizzying array of other factors that have been mentioned as possible causes, including as many as 90 gene mutations that could play a role in the development of autism. See Frank Polleaux & Gean M. Lauder, Toward a Developmental Neurobiology of Autism, 10 Mental Retardation and Dev. Disabilities Research Rev. 303, 309, 310-12 (2004). Dr. Hoffman conceded in his deposition testimony that, unless one of the genetic chromosome anomalies that is known to cause autism is identified, medical science simply does not know what causes autism. Obviously, in such a situation, the task of ruling out other plausible causes is extremely complex. In light of our decision that Dr. Hoffman failed to reliably rule in his theory of ASD causation, we need not in this case venture into the quagmire of attempting to define the parameters of a reliable process of ruling out other possible causes of autism.
Hendrix also objects to the district court's exclusion of Dr. Suhrbier's testimony. Dr. Suhrbier, G.P.'s treating physician, sought to testify as an expert witness under Rule 702. In order to be admitted into evidence, Dr. Suhrbier's opinions must also be based on a scientifically reliable methodology under Daubert. See United States v. Henderson, 409 F.3d 1293, 1299-1300 (11th Cir.2005). Dr. Suhrbier purported to both perform a differential etiology and to look for a unifying theory to explain G.P.'s ASD and syringomyelia. Like Dr. Hoffman, he concluded that the most likely cause of [G.P.]'s autism and syringomyelia was the trauma that he sustained in that motor vehicle accident in April of 2002. Unlike Dr. Hoffman, however, Dr. Suhrbier did not even attempt to provide any evidence to support a general causal link between traumatic brain injury and ASD. He presented no medical literature, described no relevant physiological process, and provided no other support for his conclusion that traumatic brain injury can cause autism. Based on the Daubert requirements for admitting expert testimony, we cannot say that the district court abused its discretion in determining that there was too great an analytical gap between Dr. Suhrbier's evidence and conclusions regarding G.P.'s ASD diagnosis to submit those conclusions to the jury. [14]