Last week, the Maryland Court of Special Appeals reversed a plaintiffs’ verdict in Dixon v. Ford Motor Company, 2012 WL 2483315 (Md. App. June 29, 2012).  Jane Dixon died of pleural mesothelioma.  The plaintiffs, her survivors, claimed that her last illness and death were caused by her household improvement projects, which involved exposure to spackling/joint compound, and by her husband’s work with car parts and brake linings, which involved “take home” exposure on his clothes.  Id. at *1.

All the expert witnesses appeared to agree that mesothelioma is a “dose-response disease,” meaning that the more the exposure, the greater the likelihood that a person exposed will develop the disease. Id. at *2.  Plaintiffs’ expert witness, Dr. Laura Welch, testified that “every exposure to asbestos is a substantial contributing cause and so brake exposure would be a substantial cause even if [Mrs. Dixon] had other exposures.” On cross-examination, Dr. Welch elaborated upon her opinion to explain that any “discrete” exposure would be a contributing factor. Id.

Welch, of course, criticized the entire body of epidemiology of car mechanics and brake repairmen, which generally finds no increased risk of mesothelioma above overall population rates.  With respect to the take-home exposure, Welch had to acknowledge that there were no epidemiologic studies that investigated the risk of wives of brake mechanics.  Welch argued that the studies of car mechanics did not involve exposure to brake shoes as would have been experienced by brake repairmen, but her argument only served to make her attribution based upon take-home exposure to brake linings seem more preposterous.  Id. at *3.  The court recognized that Dr. Welch’s opinion may have been trivially true, but still unhelpful.  Each discrete exposure, even as attenuated as a take-home exposure from having repaired a single brake shoe may have “contributed,” but that opinion did not help the jury assess whether the contribution was substantial.

The court sidestepped the issue of fiber type, and threshold, and honed in on the agreement that mesothelioma risk showed a dose-response relationship with asbestos exposure.  (There is a sense that the court confused the dose-response concept to mean no threshold.)  The court credited hyperbolic risk assessment figures from the United States Environmental Protection Agency, which suggested that even ambient air exposure to asbestos leads to an increase in mesothelioma risk, but then realized that such claims made the legal need to characterize the risk from the defendant’s product all the more important before the jury could reasonably have concluded that any particular exposure experienced by Ms. Dixon was “a substantial contributing factor.”  Id. at *5.

Having recognized that the best the plaintiffs could offer was a claim of increased risk, and perhaps crude quantification of the relative risks resulting from each product’s exposure, the court could not escape that the conclusion that Dr. Welch’s empty recitation of “every exposure” is substantial was nothing more than an unscientific and empty assertion.  Welch’s claim was either tautologically true or empirical nonsense.  The court also recognized that risk substituting for causation opened the door to essentially probabilistic evidence:

“If risk is our measure of causation, and substantiality is a threshold for risk, then it follows—as intimated above—that ‘substantiality’ is essentially a burden of proof. Moreover, we can explicitly derive the probability of causation from the statistical measure known as ‘relative risk’ … .  For reasons we need not explore in detail, it is not prudent to set a singular minimum ‘relative risk’ value as a legal standard.¹² But even if there were some legal threshold, Dr. Welch provided no information that could help the finder of fact to decide whether the elevated risk in this case was ‘substantial’.”

Id. at *7.  The court’s discussion here of “the elevated risk” seems wrong unless we understand it to mean the elevated risk attributable to the particular defendant’s product, in the context of an overall exposure that we accept as having been sufficient to cause the decedent’s mesothelioma.  Despite the lack of any quantification of relative risks in the case, overall or from particular products, and the court’s own admonition against setting a minimum relative risk as a legal standard, the court proceeded to discuss relative risks at length.  For instance, the court criticized Judge Kozinski’s opinion in Daubert, upon remand from the Supreme Court, for not going far enough:

“In other words, the Daubert court held that a plaintiff’s risk of injury must have at least doubled in order to hold that the defendant’s action was ‘more likely than not’ the actual cause of the plaintiff’s injury. The problem with this holding is that relative risk does not behave like a ‘binary’ hypothesis that can be deemed ‘true’ or ‘false’ with some degree of confidence; instead, the un-certainty inherent in any statistical measure means that relative risk does not resolve to a certain probability of specific causation. In order for a study of relative risk to truly fulfill the preponderance standard, it would have to result in 100% confidence that the relative risk exceeds two, which is a statistical impossibility. In short, the Daubert approach to relative risk fails to account for the twin statistical uncertainty inherent in any scientific estimation of causation.”

Id. at *7 n.12 (citing Daubert v. Merrell Dow Pharms., Inc., 43 F.3d 1311, 1320-21 (9th Cir.1995) (holding that that a preponderance standard requires causation to be shown by probabilistic evidence of relative risk greater than two) (opinion on remand from Daubert v. Merrell Dow Pharms., 509 U.S. 579 (1993)).  The statistical impossibility derives from the asymptotic nature of the normal distribution, but the court failed to explain why a relative risk of two must be excluded as statistically implausible based upon the sample statistic.  After all, a relative risk greater than two, with a lower bound of a 95% confidence interval above one, based upon an unbiased sampling, suggests that our best evidence is that the population parameter is greater than two, as well.  The court, however, insisted upon stating the relative-risk-greater-than-two rule with a vengeance:

“All of this is not to say, however, that any and all attempts to establish a burden of proof of causation using relative risk will fail. Decisions can be – and in science or medicine are – premised on the lower limit of the relative risk ratio at a requisite confidence level. The point of this minor discussion is that one cannot apply the usual, singular ‘preponderance’ burden to the probability of causation when the only estimate of that probability is statistical relative risk. Instead, a statistical burden of proof of causation must consist of two interdependent parts: a requisite confidence of some minimum relative risk. As we explain in the body of our discussion, the flaws in Dr. Welch’s testimony mean we need not explore this issue any further.⁴⁴”

Id. (emphasis in original).

And despite having declared the improvidence of addressing the relative risk issue, and then the lack of necessity for addressing the issue given Dr. Welch’s flawed testimony, the court nevertheless tackled the issue once more, a couple of pages later:

“It would be folly to require an expert to testify with absolute certainty that a plaintiff was exposed to a specific dose or suffered a specific risk. Dose and risk fall on a spectrum and are not ‘true or false’. As such, any scientific estimate of those values must be expressed as one or more possible intervals and, for each interval, a corresponding confidence that the true value is within that interval.”

Id. at 9 (emphasis in original; internal citations omitted).  The court captured the frequentist concept of the confidence interval as being defined operationally by repeated samplings and their random variability, but the confidence of the confidence interval means that the specified coefficient represents the percentage of all such intervals that include the “true” value, not the probability that a particular interval, calculated from a given sample, contains the true value.  The true value is either in or not in the interval generated from a single sample risk statistic.  Again, it is unclear why the court was weighing in on this aspect of probabilistic evidence when plaintiffs’ expert witness, Welch, offered no quantitation of the overall risk or of the risk attributable to a specific product exposure.

The court indulged the plaintiffs’ no-threshold fantasy but recognized that the risks of low-level asbestos exposure were low, and likely below a doubling of risk, an issue that the court stressed it wanted to avoid.  The court cited one study that suggested a risk (odds) ratio of 1.1 for exposures less than 0.5 fiber/ml – years.  See id. at *5 (citing Y. Iwatsubo et al., “Pleural mesothelioma: dose-response relation at low levels of asbestos exposure in a French population-based case-control study,” 148 Am. J. Epidemiol. 133 (1998) (estimating an odds ratio of 1.1 for exposures less than 0.5 fibers/ml-years).  But the court, which tried to be precise elsewhere, appears to have lost its way in citing Iwatsubo here.  After all, how can a single odds ratio of 1.1 describe all exposures from 0 all the way up to 0.5 f/ml-years?  How can a single odds ratio describe all exposures in this range, regardless of fiber type, when chrystotile asbestos carries little to no risk for mesothelioma, and certainly orders of magnitude risk less than amphibole fibers such as amosite and crocidolite.  And if a low-level exposure has a risk ratio of 1.1, how can plaintiffs’ hired expert witness, Welch, even make the attribution of Dixon’s mesothelioma to the entirety of her exposure, let alone the speculative take-home chrysotile exposure involved from Ford’s brake linings?  Obviously, had the court posed these questions, it would it would have realized that “it is not possible” to permit Welch’s testimony at all.

The court further lost its way in addressing the exculpatory epidemiology put forward by the defense expert witnesses:

“Furthermore, the leading epidemiological report cited by Ford and its amici that specifically studied ‘brake mechanics’, P.A. Hessel et al., ‘Meso-thelioma Among Brake Mechanics: An Expanded Analysis of a Case-control Study’, 24 Risk Analysis 547 (2004), does not at all dispel the notion that this population faced an increased risk of mesothelioma due to their industrial asbestos exposure. … When calculated at the 95% confidence level, Hessel et al. estimated that the odds ratio of mesothelioma could have been as low as 0.01 or as high as 4.71, implying a nearly quintupled risk of mesothelioma among the population of brake mechanics. 24 Risk Analysis at 550–51.”

Id. at *8.  Again, the court is fixated with the confidence interval, to the exclusion of the estimated magnitude of the association!  This time, after earlier shouting that it was the lower bound of the interval that matters scientifically, the court emphasizes the upper bound.  The court here has strayed far from the actual data, and any plausible interpretation of them:

“The odds ratio (OR) for employment in brake installation or repair was 0.71 (95% CI: 0.30-1.60) when controlled for insulation or shipbuilding. When a history of employment in any of the eight occupations with potential asbestos exposure was controlled, the OR was 0.82 (95% CI: 0.36-1.80). ORs did not increase with increasing duration of brake work. Exclusion of those with any of the eight exposures resulted in an OR of 0.62 (95% CI: 0.01-4.71) for occupational brake work.”

P.A. Hessel et al., “Mesothelioma Among Brake Mechanics: An Expanded Analysis of a Case-control Study,” 24 Risk Analysis 547, 547 (2004).  All of Dr. Hessel’s estimates of effect sizes were below 1.0, and he found no trend for duration of brake work.  Cherry picking out the upper bound of a single subgroup analysis for emphasis was unwarranted, and hardly did justice to the facts or the science.

Dr. Welch’s conclusion that the exposure and risk in this case were “substantial” simply was not a scientific conclusion, and without it her testimony did not provide information for the jury to use in reaching its conclusion as to substantial factor causation. Id. at *7.  The court noted that Welch, and the plaintiffs, may have lacked scientific data to provide estimates of Dixon’s exposure to asbestos or relative risk of mesothelioma, but ignorance or uncertainty was hardly the basis to warrant an expert witness’s belief that the relevant exposures and risks are “substantial.” Id. at *10.  The court was well justified in being discomforted by the conclusory, unscientific opinion rendered by Laura Welch.

In the final puzzle of the Dixon case, the court vacated the judgment, and remanded for a new trial, “either without her opinion on substantiality or else with some quantitative testimony that will help the jury fulfill its charge.”  Id. at *10.  The court thus seemed to imply that an expert witness need not utter the magic word, “substantial,” for the case to be submitted to the jury against a brake defendant in a take-home exposure case.  Given the state of the record, the court should have simply reversed and rendered judgment for Ford.