Sufficient Evidence of an Association

Epidemiologic evidence is sufficient to conclude that there is a positive association. That is, a positive association has been observed between exposure to herbicides and the outcome in studies in which chance, bias, and confounding could be ruled out with reasonable confidence.^b For example, if several small studies that are free of bias and confounding show an association that is consistent in magnitude and direction, there could be sufficient evidence of an association. There is sufficient evidence of an association between exposure to the chemicals of interest and the following health outcomes:

• Soft-tissue sarcoma (including heart), 1994 (year of IOM finding), 1990 (year of VA service-connection decision)

• Non-Hodgkin’s lymphoma, 1994, 1990

• Chronic lymphocytic leukemia (including hairy-cell leukemia and other chronic B-cell leukemias) (category clarification since Update 2006), 2003, 2004

• Hodgkin’s disease, 1994, 1995

• Chloracne, 1994, 1985

Limited or Suggestive Evidence of an Association

Epidemiologic evidence suggests an association between exposure to herbicides and the outcome, but a firm conclusion is limited because chance, bias, and confounding could not be ruled out with confidence. For example, a well-conducted study that had strong findings in accord with less compelling results from studies of populations with similar exposures could constitute such evidence. There is limited or suggestive evidence of an association between exposure to the chemicals of interest and the following health outcomes: