Lifetime risk estimates are used to provide a summary of the effect of radiation exposure that is independent of the length of time an exposed group is monitored and to compare the effect of specific radiation exposures in different populations.

Lifetime risk has two components. One concerns the chance that a person exposed to a given amount of radiation under some specified conditions will suffer from a disease associated with that exposure. The second component involves the average amount of life that is lost due to the occurrence of a radiation-associated disease.

The computation of lifetime risk estimates involves a number of considerations, including the population to which risks are being applied, the choice of a standard population, the handling of death rates, how excess risks are extrapolated beyond what is known from the current follow-up, and how risk estimates obtained from the experience of the atomic-bomb survivors are applied to other populations.