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September 04, 2018 Practice Points

Evidence Must Show What Is Fact and What is Just Opinion

By Brendan H. Fitzpatrick and Jessica P. Butkera

Two recent opinions from Maryland’s high court suggest that an expert in a toxic exposure case must rely on well-controlled epidemiological studies that account for confounding factors and alternatives for a sufficient factual basis to establish general causation. Challenges to plaintiffs’ experts’ causation opinions in the cases, based on the same evidence, had different outcomes. These results reflect the court’s rigorous review of what the epidemiological evidence did or did not support, which determined whether there was (1) a sufficient factual basis for the opinions and (2) an “analytical gap” between the factual basis and opinion.

In 2017, Maryland’s Court of Appeals issued Rochkind v. Stevenson, 164 A.3d 254 (Md. 2017), which examined whether an expert had a sufficient factual basis to offer general causation testimony that lead exposure can cause Attention Deficit Hyperactivity Disorder (ADHD). Plaintiff's expert testified that epidemiological studies collected in the U.S. Environmental Protection Agency's Integrated Science Assessment for Lead (EPA-ISA) demonstrated that children with blood lead levels similar to those of the plaintiff could have attention problems, learning disabilities, or ADHD. Rochkind at 257–58. Although the expert admitted this study did not establish a causal link between ADHD and lead—she merely evidenced an association between children with high blood lead levels and the symptoms of ADHD—she ultimately concluded that lead exposure caused the plaintiff's ADHD. Rochkind. The defense questioned whether a sufficient factual basis for that causation opinion existed.

The court, which had not yet determined the extent to which epidemiological studies can support expert testimony on causation, turned to General Elec. Co. v. Joiner, 522 U.S. 136 (1997) for guidance. In that case, the court decided on whether there was too great an “analytical gap” between the data and the opinion proffered to support the admissibility of an expert’s causation opinion. Joiner at 145–46. The court, applying Joiner’s analytical gap test, noted that the studies found “a causal relationship between lead exposure and [ADHD],” but did not support a causal relationship between lead exposure and a clinical ADHD diagnosis. Rochkind at 261–62. Although the EPA-ISA contained studies that examined the relationship, it was one of association, not causation. Rochkind at 291–92. The EPA-ISA cautioned that research showing an association between lead exposure and ADHD failed to account for confounding factors such as familial history, parenting, and socio-economic status. Rochkind at 263. Thus, the opinion suffered from an analytical gap. Rochkind at 262.

The court recently revisited this subject in Sugarman v. Liles, 2018 WL 3642143 (Md. July 31, 2018). Here, a plaintiff alleged lead paint caused attention deficits in the areas of auditory encoding and processing speed rather than ADHD. The defendant made a Rule 5-702 challenge to the general causation opinions, arguing that the opinions were not supported with a sufficient factual basis and should not be accepted. The Sugarman courtconcluded there was no analytical gap because the epidemiology studies recognized a causal link between lead exposure and the claimed injuries.

The court explained that if the epidemiological research “properly accounts for potential confounding factors and concludes that exposure to the agent is what increases the probability of contracting the disease, the study has demonstrated general causation—that exposure to the agent ‘is capable of causing the illness in the general population.’” Sugarman at 12. Looking again at the EPA-ISA, the Sugarman court found that the EPA had “scrutinized the evidence, received peer input, and ultimately evaluated the weight of that evidence to reach conclusions about causal determinations or the lack thereof.” Sugarman at 11–12. The court pointed to the EPA’s methodology for finding causation from association which required “multiple high quality studies” in which “chance, bias, and confounding factors could be ruled out with reasonable confidence.” Sugarman at 12. The court then determined that there was a sufficient factual basis for the expert’s opinion that auditory encoding and processing speed were within the realm of attention decrements caused by lead because such deficits were identified in the EPA-ISA as causally related with lead exposure. Sugarman at 13, 16. With such a sufficient factual basis, the general causation opinion did not suffer from an analytical gap, unlike the opinion in Rochkind. Sugarman at 15.

The court appears to be setting a standard that plaintiff’s experts must rely on epidemiological data that is well-controlled, accounts for confounding factors, and rules out alternative explanations to establish causation in toxic exposure cases. Practitioners in Maryland should carefully consider this in their discovery and motions practice.


Brendan H. Fitzpatrick is a partner in Goldberg Segalla LLP’s Baltimore office and a co-chair of the Environmental and Toxic Tort Subcommittee of the Section of Litigation’s Mass Torts Committee. Jessica P. Butkera is an associate in Goldberg Segalla LLP’s Baltimore office. They are both members of the firm’s toxic tort and environmental practice group.

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