CML incidence versus age at radiation exposure for different dose groups. Japanese atomic bomb survivors were partitioned into 3 dose groups, low (D < 0.02 Sv), medium (0.02 Sv < D < 1 Sv), and high (D > 1 Sv), and 3 age-at-exposure groups age < 20 years, 20 < age < 40 years, and age > 40 years. Person-year weighted averages of age at exposures are plotted on the x-axis; CML cases diagnosed between 1950 and 1987 divided by corresponding person-years are shown on the y-axis. In the high-dose group, incidences are 1.5, 3.2, and 1.8 per 10⁴ person-years at average age at exposures of 10.9, 29.0, and 47.4 years. In the low- and medium-dose groups, small values for childhood exposures are mainly due to the fact that people in this age group were just reaching ages of high incidence in 1987, that is, approximate independence of age at exposure is likely to hold even better when post-1987 data are added..