On January 2, 2024, the United States District Court for the Eastern District of Michigan issued an order to exclude the expert testimony of Dr. Robert Michaels in a series of cases related to the corrosive water in Flint, Michigan. Carthan, et al. v. Snyder et al, No. 5:16-cv-1044 (E.D. Mich. 2024). The court held that Dr. Michaels, in applying a methodology commonly employed by epidemiologists known as the Bradford Hill guidelines, failed to establish an association between corrosive water and skin and hair conditions, and without such, the testimony was unreliable and could not be used to infer causation between Flint water and reported skin rashes and hair loss. 

Dr. Michaels holds an M.S. in Environmental Ecology and a Ph.D. in Environmental Toxicology. He is also the president of RAM TRAC Corporation, a company which provides health risk assessment and management service. The Plaintiffs retained him to present his opinion on whether corrosive water conditions can cause certain types of skin rashes and hair loss. To support his opinions, Dr. Michaels sought to rely on a report by the Unified Coordination Group, titled Flint Rash Investigation (2016), which concluded that inconsistent water quality in Flint “may have contributed to the onset or worsening of irritant effects among individuals using the water.”

In reaching his conclusions, Dr. Michaels applied what are known as the “Bradford Hill” guidelines.  Epidemiologists often apply the Bradford Hill guidelines in order to “distinguish a causal connection from a mere association.” The Bradford Hill guidelines require consideration of the following criteria: (1) a threshold identification of an association between an exposure and a disease, and then evaluation and analysis of (2) the strength of the association, (3) the consistency across different circumstances, (4) specificity, (5) temporality, (6) dose-response relationships, (7) scientific coherence and plausibility of a causal relationship, (8) replication through experimentation, and (9) whether the association can be support by analogies to similar exposures. 

Veolia North America LLC, Veolia North America, Inc., and Veolia Water North America Operating Services, LLC (collectively referred to as “VNA”), one of several defendants in the trial slated to begin on February 13, 2024, filed a motion to exclude Dr. Michaels’ testimony.  VNA argued that Dr. Michaels’ testimony was inadmissible because Dr. Michaels misapplied the elements of the Bradford Hill causation analysis and relied on the wrong type of data.   

In evaluating the admissibility of Dr. Michaels’ testimony, the court applied the standard set forth in Federal Rule of Evidence 702 and the Supreme Court’s analysis from Daubert v. Merrell Dow Pharmaceuticals, Inc., 509 U.S. 579 (1993). Rule 702 and Daubert specify that to be admissible, expert testimony must be reliable.

As a preliminary matter, the court explained that there was no dispute that, in general, the Bradford Hill guidelines are a reliable method of inferring causation for purposes of Federal Rule 702.  However, each application of the guidelines is distinct and must be analyzed for reliability separately, the court explained.  To reliably apply the Bradford Hill guidelines, an expert must at minimum, explain how conclusions are drawn from each such criterion of the Bradford Hill guidelines, and how the criterion are weighed against one another.

The court began its analysis focusing on the first Bradford Hill criterion, association. The court held that Dr. Michaels failed to establish an association between corrosive water and skin rashes because the Coordination Group’s report did not follow the parameters of typical epidemiological studies. Additionally, the court noted that Dr. Michaels simply cited, without explaining, peer-reviewed epidemiological studies. The court further explained that the Coordination Group’s report was not specific to corrosivity at all, and therefore could not be used to establish an association between skin rashes and corrosive water—only between skin rashes and the Flint water generally. With respect to other Bradford Hill criterion, the court held that a “single study of a single incident is by definition insufficient to establish consistency,” and that the analogies used were unrelated to corrosive water. The court further found that Dr. Michaels’ conclusions with respect to temporality lacked “any substantive analysis or explanation.”

The court also held that Dr. Michaels’ conclusions with respect to hair loss were similarly inadmissible given that his conclusions about hair loss depended entirely on his opinion that corrosive water could cause skin rashes.  Specifically, Dr. Michaels had explained in his report that skin rashes can occur “at multiple places on the body, presumably including the scalp. And presumably, such rashes on the scalp would cause itching . . . and could stimulate scratching . . . constituting a potential cause of scalp irritation and of (at least temporary) hair loss.”  Because his conclusion that corrosive water causes skin rashes was inadmissible, so too was his conclusion about hair loss. 

As a result, the Plaintiffs failed to establish by a preponderance of the evidence that Dr. Michaels’ testimony was reliable. The holding underscores that it is not enough for an expert to merely rely upon a reliable methodology, here the Bradford Hill guidelines, but the expert must also demonstrably apply that methodology in a reliable way. 

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