What are the policy implications of use of epidemiological evidence in mass torts and public health litigation?

• Author: Ogolla, Christopher

1. Introduction A. Problems With Mass Torts Litigation II. Recent Cases Where Epidemiological Evidence Was Debated A. Vaccine Related Cases B. Non-Vaccine Related Cases III. General v. Specific Causation IV. Tensions Raised by the Epidemiological Evidentiary Standard V. Policy Implications of Epidemiological Evidence VI. Conclusion I. INTRODUCTION

   Courts sometimes deal with public health problems where the cause of harm to one individual or a group of individuals cannot be established. (1) In such cases, epidemiology is used to help define a relationship which links the harm and the cause. (2) In mass tort cases, epidemiologic studies are used either to refute or to support claims involving an increased risk of disease from exposure to a toxic substance. (3) Consequently, how to use epidemiology when deciding mass tort cases is becoming an increasingly important question in public health law. (4) Courts use epidemiological evidence to decide cases where a causal connection can be established between the exposure and the outcome. (5) In addition, courts use epidemiology for events that either have no "eyewitness or disproportionately involve certain types of products for which 'traditional' forms of evidence of causation are lacking." (6)

   Recently, epidemiology has become a familiar form of proof in mass torts litigation, and those who are considered epidemiologists are often sought as expert witnesses in these cases. (7) However, the necessary evidentiary requirement of epidemiology studies occasionally does not coincide well with the basic principles of causation in tort law. (8) For example, even when presented with overwhelming epidemiological evidence, juries have sometimes returned a verdict for plaintiffs, (9) which indicates that some juries are not convinced by epidemiological evidence.

   There are two imperative questions here: (1) how does epidemiology affect mass tort litigation; and (2) what relative weight should the courts give to epidemiological evidence? These questions are particularly significant in the area of causation. In order to establish causation, the plaintiff must demonstrate that it is "more probable than not" that the harm being complained of would not have occurred had the defendant followed the appropriate standard of care. (10) From prior case law, courts have derived rules for causation, namely the "but for" test and the "substantial factor test." (11) Under the first test, the defendant's conduct is deemed to be a cause of the harm "if the [harm] would not have occurred but for that conduct." (12) However, under the second test, the defendant's conduct is a cause of the harm if that conduct was a substantial factor in producing the harm. (13)

   The plaintiff bears the burden of proving causation, which is generally an issue of fact. (14) The plaintiff must introduce support indicating a reasonable basis for the conclusion that the defendant's conduct was "more likely than not ... a cause in fact" of the outcome. (15) However, courts do not require the plaintiff to establish the case beyond a reasonable doubt. (16) The plaintiff need not entirely negate the possibility that something other than the defendant's conduct caused the harm. (17) It is sufficient for the plaintiff to introduce evidence from which a reasonable person may conclude that it is more probable than not that the defendant caused the event. (18) The preceding standard is generally known as the preponderance of the evidence standard, which means that it must be greater than fifty percent. (19) Unlike traditional tort law, which follows the preponderance of the evidence standard, epidemiology relies on statistical significance and is not necessarily based on the greater half of the evidence. (20) In public health litigation, for example, statistical evidence based on aggregate data is sometimes introduced to show that the defendants created a statistically significant increase in the likelihood that the harm would occur. (21)

   For instance, in General Electric Co. v. Joiner, the United States Supreme Court held that the district court did not abuse its discretion when it excluded expert scientific testimony proffered by the plaintiff, an electrician, as evidence that his cancer resulted from exposure to polychlorinated biphenyls ("PCBs"). (22) The plaintiff attempted to prove causation by introducing epidemiological studies involving workers who had been exposed to PCBs and experienced a statistically significant increase in lung cancer deaths, especially where the workers had been exposed to numerous potential carcinogens. (23) The plaintiff relied on four epidemiological studies. (24) However, the studies were not a sufficient basis for the experts' opinions. (25)

   To begin with, from the workers they examined, the authors were ultimately unwilling to suggest a link between the increase in lung cancer deaths and the PCB exposure. (26) Moreover, the third study involved exposure to a particular type of mineral oil which was not necessarily relevant to the case, and the fourth study involved exposure to numerous other potential carcinogens. (27) Had the plaintiff used the preponderance of the evidence standard, the possibility that something other than the defendant's conduct caused the harm would not have to have been entirely negated; rather, it would have been enough for the plaintiff to have introduced evidence from which a reasonable person could have concluded it was more probable than not that the defendant caused the event. (28) Here, the epidemiological standard and the legal standard diverged.

   In distinguishing between the legal standard and the epidemiological standard, Professor Gostin wrote:

   While law seeks finality and closure, scientific inquiry is continuous; while law in civil litigation makes decisions by the preponderance of evidence (greater than 50 percent), science uses statistical significance (greater than 95 percent, with a confidence limit that does not include 1.0); while law follows an adversarial method, science embraces the experimental design (the "scientific" method); while legal evidence is testimonial, scientific evidence is empirical. (29) The distinctions between the standards of proof employed in epidemiology and in law inform the central thesis of this paper. This analysis began by describing the role of epidemiology in mass torts and public health litigation. (30) It later argues that because mass torts cover such a wide area, there are several problems related to epidemiology in litigation, particularly scientific uncertainty and inconsistent factual claims. (31)

   Part II discusses recent cases where epidemiological evidence was raised and debated, distinguishing between vaccine-related and non vaccine-related cases. (32) Courts have differentiated vaccine-related cases from non-vaccine-related cases, principally because Congress enacted a vaccine act designed to compensate victims. (33) In both vaccine and nonvaccine related cases, the legal concepts of specific and general causation are extensively used. (34)

   Part III examines the two legal concepts of general and specific causation in epidemiology and how courts have tried to balance the epidemiological causation standard with general torts principles. (35) Part IV analyzes how epidemiological evidence differs from other evidence in terms of the tensions it raises for the legal system, and argues that despite these tensions, courts still hold that causation must be shown by epidemiological evidence. (36) Part V discusses the policy implications of what gets used in court and argues that reliance on human studies, as the best evidence, may be misplaced since one cannot freely experiment on human beings. (37) This section also considers whether epidemiologists should get involved in policy issues, discussing two divergent schools of thought. (38)

   The paper concludes by suggesting that although the presence of epidemiological evidence does not necessarily end the inquiry; where the evidence is available, it should be used only if the evidence meets a heightened standard. (39) The heightened standard argued for in this paper is a screening standard for admission that considers not only a doubling of the risk by the exposure, but also jury instructions that clearly inform the jury of the strengths and weaknesses of epidemiological studies. (40) The paper also calls for the American College of Epidemiology and the Council for State and Territorial Epidemiologists ("CSTE") to develop model guidelines for the use of epidemiological evidence in the courtroom. (41) These guidelines could mirror the public health law bench books developed for some states to refer to during public health emergencies. (42)

   1. PROBLEMS WITH MASS TORTS LITIGATION

   Mass tort litigation could range from products liability and negligence claims to securities litigation, antitrust, and a variety of consumer claims. (43) Since mass tort litigation covers such a wide area, there are several problems including, but not limited to, scientific uncertainty, latent disease, and future claimants. (44) Epidemiologists are often able to predict with a reasonable level of certainty that some number of individuals within a specified group will contract a disease. (45) We, however, do not know with "certainty which individuals will contract the disease and how many of those individuals will sue when their injuries become manifest." (46)

   A special committee on toxic tort litigation cited inconsistent factual claims in different proceedings as one of the big problems. (47) Inconsistent factual claims and scientific uncertainty often affect the accuracy of the epidemiological evidence. (48) For example, "the vast majority of potentially hazardous substances have not been subjected to epidemiological study, thus, creating an evidentiary gap of potential concern to the tort system." (49) Furthermore, courts hearing products liability cases have been struggling...