The recent opinion by the Vermont Supreme Court in a benzene/leukemia case (Blanchard v. Goodyear Tire & Rubber Co.) is well worth the time required to read and digest it. Building on its decision in Estate of George v. Vermont League of Cities and Towns, the court embraced critical thinking and a Bayesian approach to causal reasoning and so held that empty evidence can't change prior, or baseline, beliefs and that plaintiff's argumentum ad ignorantiam won't fly in Vermont.
Here's how it went.
Plaintiff's claim can be distilled to the following:1) plaintiff has lymphoma of the central nervous system (CNS lymphoma); 2) CNS lymphoma is a subtype of non-Hodgkin's lymphoma (NHL); 3) benzene has been shown in some studies to double the risk of NHL; 4) plaintiff was exposed to benzene; 5) an alternate cause of CNS lymphoma was ruled out by his expert; so, 6) plaintiff's CNS lymphoma was caused by his benzene exposure. Q.E.D.
The Vermont Supreme Court was not convinced.
The vast majority of cases of CNS lymphoma "are of unknown etiology." Accordingly, our initial belief must be that plaintiff's CNS lymphoma is similarly likely to be of unknown etiology. So what evidence does plaintiff have that might reasonably move a sensible jury away from the belief that any given case of CNS lymphoma is due to some unknown cause and towards benzene? Plaintiff could have shown that he was exposed to a level of benzene that so increased his risk of CNS lymphoma that we ought to consider it as a likely cause. But this plaintiff couldn't show even by a rough approximation what his exposure might have been, much less that the dose experienced appreciably increased his risk of developing the disease. Then again, he could have shown that the manner or circumstances in which he was exposed, whatever the dose, has been found to the likely cause of CNS lymphoma in some similarly exposed group of individuals. But he had no evidence of that either. There was then nothing to cause a sensible person to move off the baseline belief - that plaintiff's was an ordinary disease of life.
Plaintiff next tried to argue differential diagnosis. However, the court clearly understood that an unweighed risk factor, abstract and disconnected from the circumstances (i.e. dose/exposure) in which it was detected is not the same thing as a potential cause to be weighed in a differential diagnosis or process of elimination exercise. Thus it held that any attempt to establish benzene as the cause of plaintiff's CNS lymphoma by ruling out everything else "must fail" because plaintiff couldn't demonstrate that his benzene exposure belonged among the potential causes to be considered in the first place.
The court then demonstrated that critical thinking isn't just for good scientists. Plaintiff had found an expert who could rule out one cause of CNS lymphoma and so he constructed the following argument: 1) plaintiff has CNS lymphoma; 2) some cases of CNS lymphoma are caused by an immunodeficiency disorder; 3) plaintiff doesn't have an immunodeficiency disorder; therefore, 4) benzene caused plaintiff's CNS lymphoma. The Vermont Supreme Court rejected this argument as well. The court held that when the cause of most cases of a disease is unknown the ruling out of one cause cannot be evidence in favor of some other cause.
Finally, and quite interestingly, the court briefly elaborated on its decision in George; the George ruling has received criticism from those hoping to lower the barriers meant to keep out all but sound science. The court holds, it seems, to the same view as organizations like the National Academies of Science and the U.S. Preventive Services Task Force - that experts weighing scientific studies ought to be able to say how they did the weighing and to state "the weight given to each study." There is, after all, not much left of the scientific method without measurements and methods.
David Oliver is managing partner of the Houston office of Vorys, Sater, Seymour and Pease. His practice focuses on civil litigation involving allegations of injuries due to exposure to chemicals or pharmaceuticals; he holds degrees in both chemistry and biology. Read more of David’s work on his blog: Mass Torts: State of the Art. You may contact David through the firm’s website at www.vorys.com.