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INTERIM FINDINGS AND RECOMMENDATIONS 13 of Agent Orange remaining after the conflict ranged from less than 0.05 to almost 50 parts per million (NAS, 1974; Young et al., 1978~. Thus, a biomarker study even one focused on TCDD-contaminated herbicides- would not necessarily yield reliable information on the herbicide expo- sure of veterans. Those limitations do not preclude the use of biomarkers or environ- mental sampling in properly constructed and conducted studies. Indeed, the committee believes that such work is desirable and that the additional information gained from it may lead to refinements of the model. As stated above, however, the committee believes that other available infor- mation is sufficient to conclude that the exposure-assessment model is feasible. OBSERVATIONS REGARDING FUTURE RESEARCH The committee does not have specific recommendations regarding the type of epidemiologic studies, outcomes, and study populations that should be pursued. It believes that such details are best left to the re- searchers who are proposing to carry out the work. It can, however, offer some general observations. Candidate health outcomes for initial study include those for which the committees responsible for the Veterans and Agent Orange series of reports have found sufficient evidence of an association with exposure. If the evidence regarding a health outcome is classified as "sufficient", it means that "a positive association has been observed between [herbicide or dioxin exposure] and the outcome in studies in which chance, bias, and confounding can be ruled out with reasonable confidence" (IOM, 1994~. There could thus be some reasonable, externally validated expectation that an association might be observed in an epidemiologic study of Viet- nam veterans. Appendix A provides the results of sample power calcula- tions to estimate the number of subjects that would be needed to conduct an informative study of one of these health outcomes. There are several potential candidate populations for such a study. In their 54-month progress report, the Columbia University researchers noted that a study that used a group of veterans that had previously been identified for research or administrative purposes might be initiated rela- tively easily. Examples include cohorts drawn from the VA Agent Orange Registry, III Corps combat battalions for which location data exist in al- ready-identified National Archives data sources, and cohorts whose loca- tions were documented by the US Armed Services Environmental Sup- port Groupie as part of previous VA epidemiologic studies. Some military A Now the Center for Research of Unit Records.