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provides a foundation for the Committee’s specific recommendations in Chapter 12, which outlines a classification system for characterizing the strength of evidence in support of a general causal relationship. Assuming that such a causal relationship has been established, Chapter 9 discusses how to quantify the strength of the causal effect, using measures most relevant to compensation decisions under the presumptive process: the attributable fraction for the population of exposed veterans, and the probability of causation for an individual. Chapter 10 covers the various types of data necessary to assess the existence of a causal relationship and to quantify the size of the causal effect. It proposes future comprehensive exposure and health data collection strategies for military personnel and veterans.

Provision of compensation to a veteran, or to any other individual who has been injured, on a presumptive basis requires a general decision as to whether the agent or exposure of concern has the potential to cause the condition or disease for which compensation is to be provided, in at least some individuals, and a specific decision as to whether the agent or exposure has caused the condition or disease in the particular individual or group of individuals. The determination of causation for veterans is based on review and evaluation of all relevant evidence including (1) measurements and estimates of exposures of military personnel during their service, if available; (2) direct evidence on risks for disease in relation to exposure from epidemiologic studies of military personnel; (3) other relevant evidence, including findings from epidemiologic studies of nonmilitary populations who have had exposure to the agent of interest or to similar agents; and (4) findings relevant to plausibility from experimental and laboratory research. Scientists and scientific organizations, such as the Institute of Medicine (IOM), have developed approaches for reviewing evidence and determining if causation can be inferred. Typically, these approaches involve a comprehensive review and the judgment of a panel of experts as to whether the evidence supports causation and with what degree of strength. The determination of causation for a particular veteran is based first on the general determination as to whether the exposure causes disease, and then on information on the exposures and possibly on clinical features of the individual being evaluated for compensation.

Compensation decisions critically depend on determinations of cause, but the information available for determining general or specific causation may be incomplete or inconclusive. For a group, the evidence may be insufficient or still evolving, and for an individual, information on exposure may be lacking, or there may be uncertainty as to the role of service-related factors versus the roles of other factors in causation. In the Agent Orange example, information on cancer risk in exposed veterans was not available until they had been followed for a sufficient time, reflective of the latency

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