Opinion ID: 1919140
Heading Depth: 1
Heading Rank: 12

Heading: General Concepts

Text: Epidemiological evidence identifies agents that are associated with an increased disease risk in groups of individuals, it quantifies the excess disease that is associated with an agent, and it provides a profile of an individual who is likely to contract a disease after being exposed to the agent. [18] In short, [e]pidemiological studies examine existing populations to attempt to determine if there is an association between a disease or condition and a factor suspected of causing that disease or condition. [19] And a study may show a positive or negative association or no association. Epidemiologists use three types of studies to determine whether an association exists between a suspected agent and a disease: (1) experimental trials, (2) cohort studies, and (3) case-control studies. The latter two types are observational studies. Here, the experts relied on observational studies. In observational studies, researchers `observe' a group of individuals who have been exposed to an agent of interest, such as cigarette smoking or an industrial chemical. [20] They then compare the exposed group's rate of disease or death incidences to the rate in another group of individuals who have not been exposed. [21] In cohort studies, researchers first identify an exposed group and an unexposed group. They then compare the rates of disease in each group. [22] In contrast, in case-control studies, researchers first identify a group of individuals with the disease and select a comparison group of individuals without the disease. They then compare the past exposures of both groups to see if an association exists between the past exposures and incidences of disease. [23] In sum, epidemiological studies assess the existence and strength of associations between a suspected agent and a disease or condition. But an association is not equivalent to causation. [24] [E]pidemiology cannot objectively prove causation. [25] Instead, epidemiological studies show the degree of statistical relationship between two or more events or variables. Events are said to be associated when they occur more or less frequently together than one would expect by chance. [26] In contrast, [e]pidemiologists use causation to mean that an increase in the incidence of disease among the exposed subjects would not have occurred had they not been exposed to the agent. [27] [7] Although epidemiological studies cannot prove causation, they can provide a foundation for an epidemiologist to infer and opine that a certain agent can cause a disease. Epidemiologists and other experts who are qualified to interpret the data and results of these studies assess causality by looking at a study's strengths and weaknesses. They then judge how the study's findings fit with other scientific knowledge on the subject. [28] [8] We discussed epidemiology and causation in Schafersman v. Agland Coop. [29] We stated that when a party uses epidemiological evidence in legal disputes, the study's methodological soundness and its use in resolving causation require answering three questions. First, does the study reveal an association between an agent and disease? Second, did any errors in the study contribute to an inaccurate result? Third, is the relationship between the agent and the disease causal? [30]