Use of Human Epidemiology Studies in Proving Causation

Article excerpt

Epidemiology studies can be used to establish only general causation, but there are many criteria that can be employed to test those studies

EPIDEMIOLOGY studies examine populations--generally smaller subsets or samples of populations--in an attempt to determine whether there is an association between exposure to a substance or factor and subsequent disease or injury. These studies are commonly used in the courts to support or refute claims that exposure to a substance or factor caused a disease or an injury in a specific plaintiff or group of plaintiffs.

The problems are (1) on what issues are epidemiological studies properly used and admitted in evidence, and (2) how a particular study was carried out and effect that may have on its admissibility.(1)

USE AND ADMISSION

A. Relevance

Epidemiology studies are relevant only to general causation. To satisfy the burden of proving causation, plaintiffs must show both (1) general causation--that is, whether the exposure or substance is capable of causing the alleged disease or injury, and (2) specific causation--that is, whether the exposure or substance actually caused the disease or injury in the specific case at issue.(2) Results from epidemiology studies are relevant only to the issue of general causation and cannot establish whether an exposure or factor caused disease or injury in a specific individual.(3) Unless general causation has been established evidence of specific causation in an individual plaintiff is not relevant and not admissible.

B. Necessity

Human epidemiology studies are a primary and generally accepted methodology to investigate the existence of a causal relationship between exposure to a factor and subsequent disease or injury. They have been held to be the most useful and conclusive type of evidence and that they must be taken into account.(4) Depending on philosophical views and the facts of particular cases, courts have made varied pronouncements regarding the necessity of epidemiology studies in causal analysis.

Many courts have held that it is necessary to offer epidemiology evidence to prove causation.(5)

Courts have held that epidemiological studies are necessary to prove causation, but only if there is no biological evidence of a causal mechanism for the disease. For instance, in Daubert v. Merrell Dow Pharmaceuticals Inc. at the district court level, the court stated: "Absent a scientific understanding of the cause of [the injury or disease], causation may be shown only through reliance upon epidemiological evidence."(6)

Courts also have held that epidemiology studies are valuable but not dispositive of the causation issue. Epidemiology studies do not always prevail over non-epidemiological evidence.(7)

In inexplicable rulings that seem to beg the question of the necessity of epidemiology studies, a few courts have stated that epidemiology evidence should be required only when they are available or if it is possible to gather the data.(8) The far better view, and that consistent with the Supreme Court's directions in Daubert, is that tort cases must be decided on the basis of the best available scientific evidence at the time of trial. Dispute resolution in the tort system cannot wait or be undermined by the creation of lower standards simply because epidemiology evidence is not currently available. As the Fifth Circuit said in Moore v. Ashland Chemical Co.: "In sum, the law cannot wait for future scientific investigation and research. We must resolve cases in our courts on the basis of scientific knowledge that is currently available."(9)

To round out all permutations, some courts have flatly held that epidemiology evidence is not required to prove causation in an exposure case.(10)

CONDUCT

Epidemiology studies must be conducted properly and utilized in the legal context following the scientific method. This approach contemplates at least five steps in the reasoning process:

* Formulation of the hypothesis or research question;

* Preparation of a written protocol or study plan that provides, in advance of gathering any data, the methodology to be followed in the study;

* Execution of the protocol, that is, gathering data from the population specified using the methodology prescribed in the research plan;

* Analysis of the data using the statistical methodology prescribed in advance in the protocol; and

* Drawing permissible conclusions, if any, from the study results, including determining whether the study results ought to be utilized at all in forming conclusions or generalizing findings to the population at large. …