tive findings for any of the aspects of scientific evidence supportive of causality enhance conviction that an observed statistical association is reliable. Such scientific evidence, of course, would include any information assembled in relation to plausible biologic mechanisms as directed in Article C. In accord with its charge, the committee examined outcome measures commonly used to evaluate statistical associations, while assessing the adequacy of control for bias and confounding and the likelihood that an observed association could be explained by chance. Additionally, the committee assessed evidence concerning biologic plausibility derived from laboratory findings in cell-culture or animal models. In particular, associations found to have multiple supportive lines of evidence were interpreted as having stronger scientific support.

In conducting its study, the present committee operated independently of the Department of Veterans Affairs (VA) and other government agencies. The committee was not asked to make and did not make judgments regarding specific cases in which individual Vietnam veterans have claimed injury from herbicide exposure. This report provides scientific information for the Secretary of Veterans Affairs to consider as VA exercises its responsibilities to Vietnam veterans. The committee was not charged to focus on broader issues, such as the potential costs of compensation for veterans or policies regarding such compensation.

In addition to the above charge, the VA made an additional request arising from the decision-making at VA necessitated by the findings of Update 2008. The sponsor asked that, when summarizing the evidence available to support the association of a health effect with exposure to the components of the herbicides used by the military in Vietnam, the committee address whether or not all the points that have rather imprecisely become known as the Bradford Hill (1965) “criteria” for causality (strength, consistency, specificity, temporality, biologic gradient, plausibility, coherence, experiment, and analogy) had been satisfied by the information available

COMMITTEE’S APPROACH TO ITS CHARGE

Following the pattern established by prior VAO committees, the present committee concentrated its review on epidemiologic studies to fulfill its charge of assessing whether specific human health effects are associated with exposure to at least one of the herbicides sprayed in Vietnam or to TCDD. The committee also considered controlled laboratory investigations that provided information on whether association between the chemicals of interest and a given effect is biologically plausible.

The VAO committees began their evaluation presuming neither the presence nor the absence of association for any particular health outcome. Over the sequence of reviews, evidence of various degrees of association, lack of association, or persisting indeterminacy with respect to a wide array of disease



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