4
Methodologic Considerations in Evaluating the Evidence

Questions To Be Addressed

The committee was charged with the task of summarizing the strength of the scientific evidence concerning the association between herbicide exposure during Vietnam service and each of a set of diseases or conditions suspected to be associated with such exposure. For each disease, the committee has determined, to the extent that available scientific data permit meaningful determinations,

  1. whether a statistical association with herbicide exposure exists, taking into account the strength of the scientific evidence and the appropriateness of the statistical and epidemiologic methods used to detect the association;
  2. the increased risk of each disease among those exposed to herbicides during Vietnam service; and
  3. whether there exists a plausible biologic mechanism or other evidence of a causal relationship between herbicide exposure and the disease.

The law establishing the committee did not provide a specific list of diseases and conditions suspected to be associated with herbicide exposure. The committee staff and members developed such a list based on the diseases and conditions that had been mentioned in the scientific literature or in legal documents that came to their attention through extensive literature searches. The committee's first step efforts was a comprehensive search of relevant computerized data bases. Sixteen data bases covering biomedical, toxicological, chemical, historical, and regulatory information were accessed. The majority of the data bases searched



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