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Article Excerpt
Epidemiology plays an important but complicated role in pharmaceutical and toxic tort litigation. Courts and scientists place greater value on epidemiologic evidence than on animal studies or human case reports and view epidemiological studies as the preferred evidence for determining the cause of disease in humans.
Epidemiology applies the scientific method to the study and comparison of groups of people, using the principles of medicine, public health, and biostatistics. Simply put, epidemiology can illuminate whether drugs cause, or are associated with, injuries.
For instance, some diseases, such as mesothelioma, occur only with exposure to a harmful agent (in that case, asbestos). More often, however, the disease or injury is not uniquely linked to the exposure. People not exposed to cigarettes still can get lung cancer, and not all cigarette smokers get lung cancer--yet we know that lung cancer is caused by cigarette smoking from multiple lines of evidence (animal studies, human case reports, experimental studies, toxicology data). Epidemiologic studies constitute the best evidence, providing a valid statistical association between exposure to cigarettes and lung cancer.
In pretrial Daubert proceedings, epidemiological studies often come under intense scrutiny, and if the results are negative (that is, not finding a valid association between exposure to the agent under study and an increased risk of the disease) or deemed unreliable, they can lead to case dismissal. (1) Even when epidemiological studies provide strong evidence in support of causation, defense lawyers and their retained experts will point out the studies' limitations--and all studies have limitations.
Jurors tend to find these studies confusing because of their complexity, and defense experts can make them more so. Many judges also misunderstand them. For these reasons, a civil jury trial is a challenging forum for presenting this type of evidence. (2)
General and specific causation
The ultimate issue in pharmaceutical litigation is causation, and a single epidemiological study does not establish causation. A study can, however, answer whether exposure to a drug is associated with an increased risk of the disease or condition under study.
Scientists recognize that causation is a judgment about the totality of experimental or epidemiological data. (3) As an amicus brief in the Daubert case noted, "By its nature, scientific evidence is cumulative: the more supporting, albeit inconclusive, evidence available, the more likely the accuracy of the conclusion." (4) Only through the accumulation of scientific evidence may a scientist infer causation. (5)
Proving causation in pharmaceutical cases requires showing that the drug is capable of causing the alleged injury (general causation) and that it was a substantial contributing cause of the plaintiff's injury (specific causation). Epidemiology is primarily used for addressing general causation but can also provide useful evidence in support of specific causation. (6)
Other evidence can help prove general causation. Case reports of the injury occurring after drug exposure provide good foundation evidence and, depending on their quality and content, can be persuasive.
Defendants downplay the value of case reports, claiming that they are merely anecdotal because there is no control group. However, if the injury has no other plausible explanation, if the timing of the injury in relation to drug exposure is striking, if the report concludes that the exposure was a likely cause of the injury based on differential diagnosis, or if the case report includes a challenge/rechallenge (where one takes a drug; watches for reactions; stops the drug; and then resumes taking it, watching for the same reactions as before), these facts can provide persuasive general causation evidence.
Other evidence that contributes to proving general causation includes animal studies and human pharmacology and toxicology experimental evidence, which provide insight into the mechanism of action (how a drug causes an injury) and biological plausibility (a causal connection that is consistent with medical knowledge). Proving the mechanism of action, although certainly helpful, is not required, and this mechanism is often, at best, only partially understood. Indeed, the manufacturers of many drugs admit they do not know how the drugs work. (7)
In 1965, scientist Austin Bradford Hill suggested various factors scientists could consider when determining whether to infer causation. (8) Each element of the so-called Hill guidelines does not have to be established to distinguish causal from noncausal associations; causation can be inferred even if some of the criteria are not met. (9)
The Hill guidelines are strength (of the association); consistency (that is, a repeated observation in different populations); specificity; temporality; biological gradient (that is, dose response); biologic plausibility;...
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