Pursuant to a congressional request, GAO discussed its recent reports on the Air Force's Ranch Hand study, which was designed to investigate whether exposure to herbicides in Vietnam led to or would lead to adverse health effects, focusing on: (1) what impact the study has had on veterans' compensation decisions; and (2) how the study disseminated results and data, communicated its limitations, and implemented measures to ensure that it was conducted with scientific independence and appropriate outside scientific oversight.

GAO noted that: (1) the Ranch Hand study has had limited impact on decisions affecting veterans' compensation; (2) its most significant impact so far has been on a decision by the Department of Veterans Affairs to provide compensation to Vietnam veterans' children born with spina bifida, but it has not contributed either positively or negatively to decisions to compensate for any other diseases; (3) the study has also led to increased discussion and further study of the association between herbicide exposure and diabetes; (4) currently, Vietnam veterans with diabetes are not eligible for compensation; (5) the relatively small size of the Ranch Hand population limits the study's ability to detect increases in risks of rare diseases, including many forms of cancer; (6) although the Air Force has conducted many aspects of the study rigorously, GAO found several past and ongoing problems, including delays in the dissemination of some results, limited public access to detailed data, inadequate communication of the study's limitations, failure to implement some measures to ensure rigor and independence, and insufficient outreach to veterans; and (7) though many of these problems have been resolved, they have led some critics to question the openness and credibility of the study.