William J. Lee, Kershaw Talley Barlow’s Scientific Director, recently published an article in The Litigator, the official publication of the Capitol City Trial Lawyers Association (CCTLA) entitled Translating Causation from Epidemiology to Law: Bradford Hill and Beyond (available here). In his article, William discusses how the Bradford Hill criteria remain a critical tool in determining causation in legal cases, but their misapplication by courts and experts often undermines the reliability of epidemiological evidence. As modern causal inference models evolve, it is crucial for the legal system to update its practices and ensure accurate translation of scientific methods to preserve justice in litigation.
Across jurisdictions in California, other states, and at the federal level, the Bradford Hill criteria remain a cornerstone for determining general and specific causation in legal cases involving epidemiological evidence. These criteria help determine whether a particular exposure generally causes or contributes to a specific injury, providing essential guidance in areas such as pharmaceutical liability cases. However, despite its widespread use, the Bradford Hill framework is often misunderstood or misapplied by key stakeholders in the litigation process, including judges, lawyers, and expert witnesses. This misapplication can undermine the admissibility and reliability of expert testimony, potentially compromising justice in personal injury cases.
The Bradford Hill criteria, established by Sir Austin Bradford Hill in 1965, include strength, consistency, specificity, temporality, biological gradient, plausibility, coherence, experiment, and analogy. Together, these factors help assess whether a correlation between a potential risk factor and a health outcome can be considered causal. However, courts often treat these criteria as rigid requirements, rather than flexible guideposts, resulting in exclusions of expert testimony over perceived gaps in meeting certain criteria. This is a fundamental misinterpretation of Bradford Hill’s intention. As Hill himself stated, "None of my nine viewpoints can bring indisputable evidence for or against the cause-and-effect hypothesis and none can be required as a sine qua non."
Additionally, while courts have relied on the Bradford Hill analysis, newer and potentially more plaintiff-favorable causal inference models—such as those developed by Rothman and VanderWeele—have not been integrated into case law. These modern approaches, widely accepted in the peer-reviewed literature, challenge outdated paradigms and emphasize a broader understanding of causality.
Moreover, judicial overreliance on statistical significance in the interpretation of epidemiological evidence can hinder justice. The U.S. Court of Appeals for the Fourth Circuit’s requirement that only statistically significant results be used in Bradford Hill analyses contradicts both Hill’s guidance and modern epidemiological practices. Hill warned against undue focus on statistical significance, stating that formal tests of significance “contribute nothing to the ‘proof’ of our hypothesis.” Today, experts caution that statistical significance can mislead, as it may not account for systematic errors or biases that distort study results.
As the field of epidemiology continues to evolve, it is crucial for the legal system to keep pace by incorporating the latest causal inference models and applying Bradford Hill’s criteria correctly. Lawyers and epidemiologists must collaborate to ensure that scientific methods are accurately translated for the courts, safeguarding the integrity of the legal process and ensuring equitable access to justice.
William J. Lee, J.D., M.S., MACE, leads the Scientific Practice Group of Kershaw Talley Barlow, P.C., a nationally recognized plaintiffs' mass tort and class action firm. William is also a leading epidemiologist, an elected Member of the American College of Epidemiology (MACE), and serves as President of the American College of Epidemiology Research and Education Foundation. He can be reached at williamlee@ktblegal.com.