Secular trend of OC incidence (ASIR) in areas at different levels of Ni (A) and As (B). ASIR increases steadily in all areas, regardless of the levels of Ni or As. However, in areas with higher level of Ni, the incidence is higher, too. For As, the levels don't correspond with the OC incidence as well as that for Ni.
Su et al. BMC Public Health 2010 10:67 doi:10.1186/1471-2458-10-67