Jim, Radiation epidemiology studies based on incidence are not uncommon, especially where interest is in seldom-lethal cancers such as those of the thyroid. A broad scale study is: Ron, E. , et al., "Cancer Incidence in atomic bomb survivors. Part IV: Comparison of incidence and mortality," Radiation Research, 137, S98-112, February 1994. Charliw Willis caw@nrc.gov