Table 2 shows the number of workers and number of incident cases for males and females by attained age (i.e., age at first incidence or end of study, 1988). The age groups with the most workers are 36–40 (males) and 31–35 (females) years. Information on person-years at risk, accumulated dose, and cancer incidence is summarized in table 3. The mean cumulative dose for nuclear power workers is much higher, and for dental workers much smaller, than for medical and for industrial workers. The average length of follow-up is 14 years, as calculated by dividing the number of person-years by the number of people