Asbestos Alert: Maryland Court Rules on Substantial Factor

by Low, Ball & Lynch

[author: Guy W. Stilson]

Dixon v. Ford Motor Company
Court of Special Appeals of Maryland (June 29, 2012) 2012WL2483315

A recent decision of the Maryland Court of Special Appeals may provide the basis for persuasive argument in California courts by defendants seeking to exclude certain expert testimony.

Joan Dixon died from pleural mesothelioma and her heirs pursued a wrongful death claim. Plaintiffs offered Dr. Laura Welch as an expert in asbestos epidemiology and proffered her opinion on causation. While Ford did not dispute Dr. Welch’s qualifications as an expert, they objected to the methods and substance of her causation opinion. The trial court denied Ford’s motion, and Dr. Welch testified “that mesothelioma in particular is a dose-response disease. Every increasing [asbestos] dose increases the likelihood of getting it,” and “every exposure to asbestos is a substantial contributing cause even if [Mrs. Dixon] had other exposures”. She also testified that every exposure to asbestos is a “substantial contributing cause” of mesothelioma. The result was a $15 million jury verdict.

The Court of Special Appeals reversed. The opinion concedes that every exposure adds to the risk of disease, that the risk of disease is proportional to the extent of the cumulative exposure, and also that there is no “safe” amount of asbestos exposure. However, decreasing exposure implies only decreasing risk. The Court found the crucial question to be: what is the extent to which various asbestos exposures increase the risk of disease? In a legal context, the issue is whether the plaintiff can show that the exposure to asbestos caused by a particular defendant was sufficiently “substantial” to support liability. “Substantiality” is essentially a burden of proof. In order for an expert’s opinion on this issue to be helpful, the expert’s testimony must help the finder of fact decide whether the elevated risk in any particular case was “substantial.”

The Dixon court determined that Dr. Welch’s opinions were not helpful and should have been excluded. The Court reasoned that “an infinitesimal change in risk cannot suffice to maintain a cause of action in tort” and therefore, Dr. Welch’s opinion that Ford had caused an exposure to asbestos in an amount that was “more than nothing” was not helpful. Dr. Welch’s statement that the exposure and increase in risk were “substantial” was not a scientific conclusion, but was simply a statement of her personal opinion in an area reserved for determination by the jury. Rather than expressing her personal opinion, Dr. Welch’s testimony should have been aimed at bridging the “analytical gap” between general epidemiological research and the situation of any particular plaintiff. Although epidemiology is a body of science devoted to making estimates of general causation among a population of people, actual causation in any particular human being lies outside the realm of epidemiology. Experts can bridge the gap “by applying the facts of the case to existing epidemiological research about general causation.” To do this, the expert “must estimate exposure and risk with reasonable scientific or medical certainty.” Dr. Welch “merely implied that there was some non-zero probability that Mrs. Dixon was exposed to asbestos from Ford’s products, and that this resulted in some non-zero increase in her risk of contracting mesothelioma. As such, Dr. Welch’s conclusion that the risk and probability of causation was ‘substantial’ provided the jury with nothing more than her subjective opinion of ‘responsibility,’ not scientific evidence of causation.” As the expert’s testimony was insufficient to support causation, the Court of Appeal reversed and remanded the matter for a new trial.


In Maryland, as in California, it is not enough to show the defendant caused a negligible exposure to asbestos. Instead, the plaintiff must show the defendant caused a substantial exposure. Determination of what is “substantial” is left to the jury.

Many plaintiff experts offer testimony similar to that which Dr. Welch offered in Dixon: that any exposure increased the risk to some degree, and that since the person developed an asbestos-related disease, that increase must be considered to have been substantial. Defendants argue that plaintiff experts should not be permitted to testify as to what is or is not a “substantial” exposure, but should instead be limited to testimony relating to the factors which will allow a jury to make the substantiality determination. These factors include frequency of exposure, proximity of the asbestos product to the injured person, proportion of exposure caused by a Defendant as compared to total exposures, and consideration of other potential causative factors, such as smoking in a lung cancer case.

The Maryland Court of Special Appeals rejected the “any amount is substantial” testimony as being unscientific and provided a well-reasoned analysis for this conclusion. Defendants now have another well-reasoned case to help persuade trial courts to reject personal opinions of plaintiff experts. The testimony of any acknowledged expert must be limited to opinions that have a sound scientific basis.

For the full decision see:


Low, Ball & Lynch’s Environmental and Toxic Torts Team has been successfully representing defendants in asbestos-related litigation for over 25 years. The Environmental and Toxic Torts Team also handles cases involving chemical spills and toxicity, lead, silica, and Proposition 65.

Contact us: Sonja Blomquist, This e-mail address is being protected from spambots, you need JavaScript enabled to view it and Guy Stilson, This e-mail address is being protected from spambots, you need JavaScript enabled to view it | Phone: 415.981.6630 | Fax: 415.399.1506



DISCLAIMER: Because of the generality of this update, the information provided herein may not be applicable in all situations and should not be acted upon without specific legal advice based on particular situations.

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