Yet another court has sent packing Dr. Sam Hammar and his "every exposure", "every breath" method of causal attribution in asbestos/mesothelioma cases. This time it was a USDC in Utah (Central Division) that ordered such testimony be excluded; essentially by adopting the late Popperian view that "an untested and potentially untestable hypothesis" isn’t the same thing as the "scientific knowledge" required by Rule 702. Ok, so why blog about it if it’s not particularly surprising? Well, because it presents an opportunity to discuss (1) the perils of reasoning by analogy and (2) why fault is invariably and inextricably bound up with causation.

Hammar, no doubt invoking the linear no-threshold dose response model for carcinogens, countered the motion to exclude his causation opinion by elaborating that his attribution of causation to every exposure is proper because no exposure can be ruled out (since every fiber carries some risk). Then, either conflating risk with causation or using the "small glasses" approach (the order doesn’t say which), Hammar concluded that if no exposure can be ruled "out" then every exposure must be ruled "in"; thereupon leading logically to his opinion that the plaintiff’s mesothelioma "was caused by his total and cumulative exposure to asbestos, with all exposures and products playing a contributing role."

The court analogized Hammar’s reasoning to that of a detective who, upon learning of a murder in a large family (and knowing that the killer is often found among family members), not only doesn’t rule anyone out but proceeds to theorize that because none may be ruled out all must thereby be ruled "in". While agreeing that refusing to rule anyone out would be reasonable the court held that the same reasoning "would not allow the detective to attribute legal liability to every family member on the basis of such a theory."

Unfortunately there are a few problems with this analogy. First, unlike family members, within categories of fiber type asbestos is fungible and no technique exists that can differentiate by origin one fiber from another. Second, the scenario appears to assume a one-hit model of causation (i.e. that only one family member was actually responsible) – which is not (nowadays anyway) the causal model plaintiffs push in these cases. Finally, and most importantly, it ignores the fact that in a real case causation doesn’t get plaintiff anywhere if he hasn’t established breach of a duty (e.g. failure to warn).

Recasting the analogy to more closely mirror a typical case yields something like the following: the detective arrives at the scene of the crime and finds identical octuplets standing around the victim who has been crushed under the weight of several large rocks. Each sibling admits to having exposed the victim to one or more of  the rocks. That I think is more analogous to what the Fifth Circuit grappled with in Borel v. Fiberboard and it illustrates why in such cases courts shift the burden of sorting it all out from the plaintiff to the defendants. It’s because no matter which defendant or which combination of defendants is held liable they’re necessarily blameworthy and no one will think an injustice has been done.

But now let’s update the analogy from 1973 to 2013. The detective arrives on the scene and finds the identical octuplets, the recently crushed victim nearby and each sibling admitting to having exposed the victim to rocks. However this time three of the siblings are found to have been responsible for nothing more than a handful of sand whereas the other five, all of whom were responsible for large rocks, are judgment-proof (thanks to bankruptcy court). Just as asbestos plaintiffs can’t find any evidence that brake work increases the risk of mesothelioma, the detective can find no report of a handful of sand ever crushing anyone. What’s a clever problem solver intent on blaming each viable defendant to do?

Hatch a "straw that broke the camel’s back" theory which makes even a single grain of sand a necessary cause. Couple it with the linear no-threshold dose response model for carcinogens such that each grain of sand carried with it some non-zero risk of death by crushing and  you’re golden –  your medical expert now gets to testify not only to causation but to the imposition of a risk, the magnitude of which (death) is enormous, on the decedent and, worse yet, without warning.

A number of courts intuit that there’s something very much wrong with the theory but often can’t quite pin down what that something might be. Here the court settled on the fact that the theory is untested and untestable. Now while it’s true that no group of people who took one and only one breath of asbestos dust can be found and compared to another (equally nonexistent) group who never inhaled so much as a fiber, and no group of individuals can ever be ethically exposed to a known carcinogen just to see what happens to them, it’s not clear why this ought to be a fatal flaw in plaintiff’s theory. First, the theory is theoretically, if not practically, falsifiable and so under Daubert would avoid the label of pseudoscience. Second, would anyone really claim that in a hypothetical case in which the plaintiff was exposed to levels of asbestos that were higher than have ever been studied before that he couldn’t recover because his theory that such massive levels of asbestos causes mesothelioma is untested and untestable? You get the point.

So if it’s not a lack of testability, what’s wrong with Hammar’s theory? The problem is that it fails to assess the risk imposed, which is to say the defendant’s conduct at the time of the conduct, and so fails to establish legal causation.

You can’t go through life without kicking up some dust and it may well be the case that sometimes it really is one last straw, or one last grain of sand, that breaks the camel’s back. But the focus of courts when deciding whether liability may justly be imposed should be on the conduct sought to be condemned. In the case of Smith v. Ford plaintiff sought to blame the defendant for a risk that was either nonexistent (as no study has ever shown an appreciably increased risk of mesothelioma among brake workers) or so small that it would take a cohort of many more people than have ever worked as brake repairmen to detect it. How can the imposition of such a risk, even if it exists, be a wrong?

It can’t, or at least it shouldn’t.