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Gatekeeping’ Expert Testimony: From Popcorn to Tires and Beyond

August 9, 2010 in  News

New York Law Journal

What do butter-flavored microwave popcorn, a tire without nylon cap plies, a child restraint system, an asbestos-containing product, the chemical phosphorous pentasulfide, and an orthopedic knee implant have in common? On the surface, not much. But in the sometimes “Wild West” shootout called products liability, each has been the subject of claims for injury, each has involved the proffer of an expert’s defect causation theory, each has undergone the scrutiny of gatekeeping judges, and each has resulted in recent rulings precluding expert testimony as unreliable.

Let’s hone in on these recent decisions and peek at what is going on. Are lawyers pushing the liability envelope too far? Are experts offering opinions without doing their homework? Are experts for hire too readily finding causal connection between product and injury? Are judges probing more searchingly in executing their gatekeeping task to admit only evidence that is both relevant and reliable? The answer may be a little of the first three and a lot of the fourth. It seems as if the claimants’ lawyers and their experts are advancing “associations” between product and injury, but the courts, as they should, are demanding reliable proofs that comport with the scientific method and that meet established reliability criteria.

Microwave Popcorn

The “microwave popcorn” case is Newkirk v. Conagra Foods Inc.,a federal court decision from the Eastern District of Washington issued on July 2. Here, a physician named David Egilman, board certified in occupational and internal medicine, was “Daubertized” via judicial gatekeeping as a result of infirmities in his opinions and methodology. The term “Daubertized” is being used here because of the famous U.S. Supreme Court decision in Daubert v. Merrell Dow Pharm. Inc.2 and its progeny calling on trial judges, among other things, to ensure that an expert witness “employs in the courtroom the same level of intellectual rigor that characterizes the practice of an expert in the relevant field.”3 The Daubert reliability criteria are reflected in Federal Rule of Evidence 702 and in analogous state evidence codes or common law rules.

The plaintiff alleged that his exposure to defendant’s popcorn with natural and artificial butter flavorings caused the lung disease condition known as bronchiolitis obliterans along with damage to his respiratory system, shortness of breath and reduced life expectancy. The products were Conagra’s Act II Butter and Act II Butter Lovers Popcorn. Plaintiff also sued suppliers of butter flavorings to Conagra. Plaintiff ate between five to seven bags of microwave popcorn each day for about 11 years and was eating the product before he reached this level of daily exposure. He began eating the product around the time he quit smoking, to suppress his appetite and avoid gaining weight.

After noticing respiratory symptoms he read an article in 2007 about a consumer developing “popcorn lung” from inhalation of butter flavoring fumes. Initial diagnosis was “obstructive lung disease” given his significant history of smoking. But then he saw another physician (one of plaintiff’s experts) who diagnosed “bronchiolitis obliterans syndrome,” as did Dr. Egilman. Other physicians, however, did not diagnose him with that disease. The only conclusive means of diagnosis would be a lung biopsy which has its own risks and which plaintiff did not have performed.

Diacetyl Exposures

The connection between obstructive lung disease and popcorn with butter flavorings became a matter of concern for popcorn manufacturers and their employees in 2000 and 2001. The culprit compound was identified as diacetyl, a flavoring agent used to provide a buttery taste and a sense of “creaminess.” Some popcorn plant workers who daily inhaled diacetyl in industrial-level exposures made claims. Defendant and other microwave popcorn manufacturers stopped using diacetyl in or around 2007.

Dr. Egilman’s expert opinion testimony was plaintiff’s primary evidence supporting general causation. Defendants did not contest his qualifications as an expert. He had served as an expert witness in popcorn worker cases and was being proffered in at least one other microwave popcorn consumer case. Defendants challenged his opinions as to general causation, i.e., was the substance to which plaintiff was exposed capable of causing the particular lung disease and other respiratory ailments? Dr. Egilman posited that there is no known safe level of diacetyl exposure. Studies suggest that exposure below 1 ppm can cause bronchiolitis obliterans and other respiratory illnesses.

From there he proceeded to state his opinion regarding specific causation, i.e., whether the plaintiff’s disease developed as a result of exposures to microwave popcorn vapors. He opined that plaintiff’s disease was “consistent with epidemiological evidence linking exposure of butter popcorn flavoring containing diacetyl to bronchiolitis obliterans.” Further, his symptoms were “comparable” with other known consumer cases as well as industrial cases in workers exposed in popcorn production plants. Dr. Egilman concluded “within a reasonable degree of medical certainty” that plaintiff developed lung disease as a result of inhaling flavors released by microwave popcorn.

After conducting detailed analysis, the court found that certain foundational statements were not based on sufficient facts or data. None of the submitted exhibits and reports supported the conclusion at the heart of this case: “that vapors emitted from a microwave popcorn bag contain the same proportion of chemicals or that all of the substances in the two instances are identical.” To the contrary, at least one study said that certain workers may have been exposed to volatile flavoring ingredients that were “qualitatively different” from those to which others had been exposed. There was thus an analytical gap. As Addendum B to its opinion, the court compiled many other examples of conclusions and opinions Dr. Egilman failed to document.

He also did not reliably apply principles and methodology to the facts of the case. Thus, for example, he relied on published studies but drew “conclusions far beyond what the study authors concluded.” Or, he manipulated data from those studies to “reach misleading conclusions of his own.” The methodology for his conclusions was unreliable. His opinions fell below the threshold standard of scientific validity in other ways. As the court observed, “coming to a conclusion first and then doing research to support it is the antithesis of the scientific method.”

He also extrapolated “from extremely small samples to make sweeping conclusions.” He extrapolated from animal studies to humans without offering any explanation for the “how and why” to do so. He included “legal conclusions” throughout his reports and affidavits. He was guilty of “internal contradictions” including arrival at contradictory conclusions using the same methodology. In light of the “too great” analytical gap between existing data and his conclusions on general causation, and because the bulk of his conclusions did not rise above “subjective belief or unsupported speculation,” Dr. Egilman’s opinion testimony was ruled inadmissible.

Tire Claim

The tire case is Cruz v. Bridgestone/Firestone North American Tire, LLC,4 a Tenth Circuit U.S. Court of Appeals decision issued on July 22. A footnote says the order and judgment is not binding precedent except for limited purposes but “may be cited, however, for its persuasive value” consistent with the terms and conditions of Fed. R. App. P. 32.1. The left rear tire of a 1988 GMC van suddenly deflated causing the vehicle with 12 occupants to overturn. Plaintiff’s expert, David Osborne, opined that the tire was defective because of defendant’s failure to design it with a nylon cap ply (a layer of rubberized nylon cords wrapped around the tire forming a tight band and acting like a tourniquet). This, he claimed, would have reduced the fatigue effect.

Defendant moved to exclude the testimony as unreliable, asserting that the expert conducted no tests to support his opinion; had no supporting scientific studies; had not subjected his opinions or methodology to peer review; and could not establish the rate of error for his opinions or methodology. The federal district court in New Mexico granted the motion to exclude Mr. Osborne’s testimony on the nylon cap ply theory. It then granted summary judgment to defendant.

The Tenth Circuit affirmed, finding no abuse of discretion. Mr. Osborne conducted no testing on his theory, offered no supportive peer reviewed studies, offered no empirical data and conceded that no tire standard called for use of nylon cap plies in tires. Thus, plaintiffs failed to satisfy the enumerated Daubert admissibility criteria despite Mr. Osborne having served as an international expert on tire failures and having extensively examined the accident tire.

Autism Claimed

The child restraint system case is Hendrix v. Evenflo Co. Inc.,5  a decision in the U.S. Court of Appeals for the Eleventh Circuit issued on June 22. The claim is somewhat unique. Plaintiff alleged that her 15-day-old son sustained traumatic brain injuries when the child restraint system malfunctioned during a minor traffic accident. Plaintiff claimed that the seat dislodged from its base because it had been “false-latched,” i.e., it audibly clicked leading the installer to believe it is properly latched. Plaintiff further claimed that those brain injuries caused the child to develop autism spectrum disorder (ASD) and a spinal cord defect known as syringomyelia.

The infant did suffer a closed-head injury but the parties disputed its severity. The child exhibited no developmental problems at his 2, 4 or 10-month check-ups. Some 18 months after the accident, however, the infant began to exhibit developmental problems. The child was diagnosed at age 3 as having a spinal cord cyst, which plaintiff claims is a syringomyelia that can be caused by trauma, but defendant labeled it a hydromyelia resulting from the brain’s congenital defect. At age 5 the child was diagnosed with ASD, a behaviorally defined disorder with qualitatively impaired social interaction and communication and restrictive repetitive and stereotyped patterns of behavior, interests and activities. All experts agreed that the child, as a result of his ASD, will never be gainfully employed.

Two of the doctors who served as experts (a pediatric neurologist and a medical doctor board-certified in neurodevelopmental disabilities and developmental-behavioral pediatrics) opined that the injuries sustained in the accident caused the child to develop ASD and syringomyelia. Prior to trial, the district court excluded for unreliability the experts’ opinions on the cause of the ASD. It would, however, admit the expert testimony on the second condition. At that point, though, plaintiff voluntarily dismissed the remaining claims and filed an appeal.

The Eleventh Circuit affirmed. Neither expert described whether or how traumatic brain injury could cause the child’s individual deficits. One physician talked about brain abnormalities being “strongly linked” to autism and an “association” between injury to the developing brain and later occurrence of autism. But he applied his elaborate causation theory “explicitly and unambiguously to the child’s ASD diagnosis generally and not to the impairments individually.” The other expert concluded that the trauma was the “most likely cause” of the autism but likewise did not attempt to parse the causation issue with respect to the child’s individual impairments.

The experts relied upon the “differential etiology” method (most often called “differential diagnosis”) to link the traumatic brain injury to the ASD diagnosis. But that entails a two-step analysis. First, a comprehensive list is prepared of all competing causes generally capable of causing the symptoms. Then the expert eliminates all causes but one. For each possible cause “ruled in” at the first stage, the court must ensure that the expert’s opinion on general causation is “derived from scientifically valid methodology.” Here, the district court was correct to apply the Daubert analysis to the question whether traumatic brain injury can, in general, cause autism. For example, mere temporal relationship does not prove a causal relationship.

In the second step of “differential etiology,” the expert must eliminate all causes but one. This leads to the “specific causation” inquiry. An expert must provide reasons for rejecting alternative hypotheses using scientific methods and procedures. The elimination of hypotheses “must be founded on more than subjective beliefs or unsupported speculation.” Here, the “rule in” and “rule out” steps did not meet the need to provide useful evidence of a definitive causal link between traumatic head injuries and autistic disorders.

The appellate court “carefully and exhaustively reviewed the literature cited” by the expert and agreed with the district court’s assessment. An expert’s experience and training “does not automatically render every opinion and statement by that expert reliable.” The physician’s failure to “rule out” other possible causes was an additional deficiency. The appellate panel observed that the medical literature “indicates…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.” The court quoted prior case law: “The courtroom is not the place for scientific guesswork, even of the inspired sort. Law lags science; it does not lead it.”

Asbestos Suit

The asbestos-containing product decision is Butler v. Union Carbide Corp.,6  a state trial court decision in Georgia issued on June 29. Plaintiff worked with phenolic molding compounds he said were granular and dusty and allegedly contained asbestos. Here the expert was a pathologist, John Maddox, who opined that “any exposure” to asbestos in defendant’s product can cause disease. The theory is also called the “linear non-threshold model for causation.”

Based on Georgia’s equivalent of a Daubert analysis, however, the court found that the “any exposure” or “non-threshold” theory, as admitted by Dr. Maddox himself, “is not practically testable and has not been tested.” Therefore, it failed the first of Daubert’s test for scientifically valid knowledge. Moreover, it is “improper for an expert to presume that the plaintiff must somehow have been exposed to a high enough dose to exceed the threshold [necessary to cause the illness], thereby justifying his initial diagnosis. This is circular reasoning.”

The expert’s claim that there is no known safe level of exposure does not mean that none exists; it simply means science today has not or cannot, with current scientific expertise or relying on existing studies, determine what that level of exposure is. For example, “Dr. Maddox admitted that everybody has breathed some asbestos fibers…. Yet the admitted extreme rarity of mesothelioma demonstrates that logically there is a threshold exposure for harm. Otherwise, the huge exposed population of people receiving low or even moderate doses would more frequently have this terrible disease.” Dr. Maddox also stated that there are idiopathic causes of mesothelioma. Without quantification of the dose-response and its threshold for asbestos, when does one “scientifically” rule out another cause of the disease and not asbestos?

Dr. Maddox’s “any exposure” theory is, at most, “scientifically-grounded speculation: an untested and potentially untested hypothesis.” Further, in science, a nontestable hypothesis cannot have an error rate. So Dr. Maddox’s “any exposure” theory did not meet Daubert’s “error rate” admissibility factor. Reliance by plaintiff on so-called “general acceptance” of his hypothesis is “far outweighed by its lack of scientific validity.” Further, when a proposed expert is a “quintessential expert for hire,” the trial judge should apply the Daubert factors with “greater rigor.” During Dr. Maddox’s live testimony at the hearing on the motion to exclude, his “behavior seemed much more consistent with an advocate than a dispassionate scientist/witness.” For the foregoing reasons, and more, the expert’s opinion testimony was ruled inadmissible.

Chemical; Knee Implant

The chemical phosphorous pentasulfide (P2S5) case is Barrett v. Rhodia Inc.,7 a decision by the U.S. Court of Appeals for the Eighth Circuit issued on May 24. Here a technician at a hazardous waste disposal facility brought a toxic tort action against the manufacturer of a chemical used during ash fixation to accelerate the stabilization of the waste material. If the chemical’s dust is inhaled it reacts with lung moisture to form hydrogen sulfide gas.

Plaintiff presented experts who opined a brain injury caused by hydrogen sulfide gas exposure coming from a P2S5 drum opened by another employee. Defendant’s expert presented an alternative explanation for the injuries, based on tests he performed in opening drums and gas dispersion. The drum opening exposure was too weak. Instead, plaintiff likely inhaled the dust at another point when not wearing a protective breathing apparatus.

The Eighth Circuit affirmed the district court’s exclusion of the experts’ testimony. Here, although the experts were qualified to opine on symptoms and their consistence with exposure, they were held not qualified to render opinions about the dispersal of hydrogen sulfide gas, the concentration level of the worker’s exposure or whether the injuries were caused by gas released from the opened P2S5 drum.

The knee implant case is Fuesting v. Zimmer Inc.,8 a “nonprecedential disposition” published in the Federal Appendix. Here, the expert, James Pugh, opined that the design of a knee implant that failed was defective because of oxidation caused by a deficient sterilization process. The trial court, the U.S. District Court for the Central District of Illinois, rejected a motion to exclude the opinion as unreliable, and the jury awarded plaintiff $650,000.

The U.S. Court of Appeals for the Seventh Circuit reversed, however, holding that Dr. Pugh’s testimony was unreliable. He failed: to bridge the “analytical gap between his opinion about the sterilization process and the failure of plaintiff’s implant in particular; to show his methods were subject to peer review and approval; to rule out alternative possibilities for causation; and to show that better sterilization methods were available in 1991.9 On remand, plaintiff hired a new expert, Dr. Robert Rose, whose testimony was excluded by the trial judge. On appeal (again) the Seventh Circuit held that “Dr. Rose’s testimony fails for essentially the same reasons that Dr. Pugh’s did.” The appellate court then proceeded to detail deficiencies in the reliability criteria.

Michael Hoenig is a member of Herzfeld & Rubin.


  1.  No: CV—08—273—RMP, U.S. Dist. Ct. (E.D. Wash. July 2, 2010) (Judge Rosanna Malouf Peterson).
  2.  509 U.S. 579 (1993).
  3.  Kumho Tire Co., Ltd. v. Carmichael, 526 U.S. 137, 152 (1999).
  4.  No. 08—2242 (10th Cir. July 22, 2010).
  5.  No. 09—10079 (11th Cir. June 22, 2010).
  6.  Civil Action No. 2008CA114 (Ga. Super. Ct., Morgan Co., June 29, 2010).
  7.  606 F.3d 975 (8th Cir. 2010).
  8.  362 Fed. Appendix 560 (7th Cir. 2010).
  9.  See Fuesting v. Zimmer Inc., 448 F.3d 936 (7th Cir. 2006).