According to an analysis of health surveys that the RERF conducted on some 113,000 A-bomb survivors between 1950 and 2001, the incidence of leukemia among hibakusha — or survivors of the 1945 atomic bombings of Hiroshima and Nagasaki — is about 2.5 times higher than others 55 years following the bombings.

The analysis found 312 cases of leukemia among those surveyed, of which 94 were believed to have been related to radiation exposure due to the atomic blasts. Although the risk of developing leukemia tended to decline as time passed, the study has found that those who were 10 years old at the time of the bombings — and were exposed to 1 sievert (1,000 millisieverts) of radiation — were 51.3 times more likely than others to develop leukemia five years after the bombings. The figure declined to 3.5 times after 40 years — and to 2.5 times after 55 years — following the atomic attacks.

The study also found that those who were 30 years of age at the time of the bombings were 21 times more likely to develop leukemia than others five years after the atomic blasts, which declined to 2.7 times 40 years after the bombings.

In 1994, the RERF conducted a risk survey based on data collected between 1950 and 1987, which found that the younger one was at the time of the bombings — and the less time that had passed — the higher was the risk of developing leukemia.