Veterans and Agent Orange Update 2000 (2001) / Chapter Skim
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4 Methodological Considerations in Evaluating the Evidence
4 Methodological Considerations in Evaluating the Evidence
Pages 103-109
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From page 103... ...
The committee staff and members responsible for the 1994 report Veterans and Agent Orange: Health Effects of Herbicides Used in Vietnam (hereafter referred to as VAO)
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From page 104... ...
The committee necessarily focused on a pragmatic question: What is the nature of the relevant evidence for or against a statistical association between exposure and the health outcome? The evidentiary base that the committee found to be most helpful derived from epidemiologic studies of populations that is, investigations in which large groups of people are studied to determine the association between the occurrence of particular diseases and exposure to the substances at issue.
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From page 105... ...
In pursuing the question of statistical association, the committee recognized that an absolute conclusion about the absence of association may never be attained. As in science generally, studies of health outcomes following herbicide exposure are not capable of demonstrating that the purported effect is impossible or could never occur.
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From page 106... ...
Whole-animal studies or animal-based experimental systems continue to be used to study herbicide toxicity because they allow for rigid control of chemical exposures and close monitoring of health outcomes. Because many of the chemical exposures presently associated with certain diseases in humans have been confirmed in experimental studies, data derived from such studies are generally accepted as a valuable guide in the assessment of biologic plausibility.
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From page 107... ...
This may provide a significant advantage in the assessment of biologic plausibility, because biologically based epidemiologic data allow more accurate identification and quantification of exposures. For instance, the analytical data available from individuals known to have been exposed to herbicides during the Vietnam War constitute a valuable resource for the study of TCDDrelated disease, with documented TCDD body burdens providing a quantitative bridge between experimental studies and human epidemiology.
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From page 108... ...
the nature of any doseresponse relationships, although the committee acknowledged that such findings may have only an indirect bearing on the association in veterans themselves. It is also important to note that the categories of association described below relate to the association between exposure to chemicals and health outcomes in human populations, not to the likelihood that any individual's health problem is associated with or caused by the herbicides in question.
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From page 109... ...
They could not be accomplished by adherence to a narrowly prescribed formula. Rather, the approach described here evolved throughout the process of review and was determined in important respects by the nature of the evidence, exposures, and health outcomes at issue.
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