Featured Expert Column: Judicial Gatekeeping of Expert Evidence
By Evan M. Tager, Mayer Brown LLP, with Carl J. Summers, Mayer Brown LLP
When there are multiple cumulative causes of an injury, an expert witness’s testimony attributing specific causation to one of those causes must employ a standard that at least crosses the threshold necessary to establish causation under the law. Otherwise, the testimony is unhelpful to the jurors—indeed, it may affirmatively mislead them. This principle was front and center in a decision released by the Georgia Supreme Court on July 5. In Scapa Dryer Fabrics v. Knight, the court held that an expert witness’s testimony must “fit” the pertinent causation inquiry for asbestos cases under Georgia state law.
In the late 1960s and early 1970s, the plaintiff worked at defendant Scapa Dryer Fabrics’ manufacturing facility as an independent contractor. During that time, the pipes and boilers in the defendant’s manufacturing facility were insulated with material containing asbestos, and the defendant used yarn containing asbestos to make textiles.
Nearly four decades later, the plaintiff was diagnosed with mesothelioma. The plaintiff brought a lawsuit against the defendant, claiming that the defendant negligently exposed him to asbestos at the manufacturing facility and caused his mesothelioma. The plaintiff also sued other defendants, including Union Carbide Corporation and Georgia Pacific, alleging that they, too, negligently exposed him to asbestos and thus caused his mesothelioma. Although those defendants were not parties to the appeal, their role in potentially exposing the plaintiff to asbestos is important to the court’s causation analysis.
At trial, the plaintiff proffered the expert testimony of Dr. Jerrold Abraham, a pathologist. According to Dr. Abraham, asbestos fibers occur naturally in the ambient air, but exposure to this background level of asbestos is not known to cause mesothelioma. But when someone is exposed to asbestos above the background level, Dr. Abraham opined, this cumulative exposure may exceed the amount of asbestos the lungs can absorb. Because any exposure above the background level contributes to this cumulative exposure, Dr. Abraham testified, each such exposure is a contributing cause of the resulting mesothelioma—even though the cumulative exposure necessary for a particular person to develop mesothelioma is scientifically unknowable. Dr. Abraham testified that because each cumulative exposure above background contributes to the eventual disease, a causal connection would be lacking only if there was “no asbestos exposure” attributable to the defendant. Dr. Abraham further testified that he did not need to determine the exact level of the plaintiff’s exposure at the manufacturing facility, other than that the level was greater than “zero.”
The defendant objected on the grounds that Dr. Abraham’s theory was “junk science” and that it violated causation principles under Georgia state law. The defendant also strenuously contested whether the plaintiff was exposed to any asbestos above the background level at its manufacturing facility. The trial judge admitted Dr. Abraham’s scientific testimony over the defendant’s objection.
The jury found for the plaintiff and awarded more than $4 million in damages. A divided intermediate appellate court affirmed. The Supreme Court of Georgia reversed on the ground that Dr. Abraham’s testimony did not “fit” the pertinent causation inquiry under Georgia law.
To understand the Court’s decision, a quick primer on causation in asbestos cases is useful. Under Georgia law, although a plaintiff does not have to prove that exposure to asbestos at a particular facility made a “substantial” contribution to the plaintiff’s mesothelioma, a “de minimis” contribution is insufficient. In other words, the plaintiff must show that his exposure at the defendant’s facility made a “meaningful contribution” to his disease.
The Georgia Supreme Court faulted Dr. Abraham for opining that, because any exposure above the background level contributed to the cumulative exposure and thus to causing the plaintiff’s mesothelioma, it was unnecessary to resolve the specific extent of the plaintiff’s exposure at the defendant’s manufacturing facility. In other words, Dr. Abraham misleadingly told the jury that the defendant caused the plaintiff’s disease even if the plaintiff was exposed to only a de minimis amount of asbestos at the defendant’s facility. According to the Georgia Supreme Court, “such testimony does not ‘fit’ the issue that the jury was charged with deciding, and it could not have been helpful to the jury.” Because the trial court failed to perform its gatekeeping function by allowing the jury to hear this testimony and because the testimony was at the core of the plaintiff’s case, the Georgia Supreme Court reversed.
Although rejecting Dr. Abraham’s expert testimony in the instant case, the Court went out of its way to sketch out how Dr. Abraham’s cumulative-exposure theory could potentially be admissible under Georgia law. The court opined that
if an expert coupled his reliance on the cumulative exposure theory with reliable data sufficient to show that the exposure in question [was] more than de minimis—and if the expert qualified his ultimate opinion as to causation, conditioning it upon there having been more than a de minimis exposure—the opinion then might ‘fit’ the pertinent causation inquiry, notwithstanding that the extent of exposure is disputed.
In that scenario, the jury, not the expert, would be left to decide the extent of exposure. But because Dr. Abraham did not qualify his opinion in such a fashion and failed to estimate the extent of the plaintiff’s exposure at the manufacturing facility, his testimony was inadmissible.
The Georgia Supreme Court’s decision shows the importance of causation analysis to expert testimony. By requiring that expert testimony “fit” causation principles, the Georgia Supreme Court ensured that expert witnesses cannot confuse juries by conflating their particular theory of causation with the legally applicable one. The decision also reinforces the appropriate roles of the trial judge, the expert witness, and the jury. The trial judge must serve as a gatekeeper, ensuring that the jury is exposed only to reliable expert testimony that accords with state-law principles of causation. It is the role of the expert to make his case within the bounds of state law. And it is the province of the jury to weigh the expert’s testimony and make a determination of liability based on the theories presented by the parties.