Fig. 1.

Potential relationship among atomic bomb radiation, observed and unobserved factors and mortality of individuals exposed in utero is illustrated. Factors framed with solid line indicates observed variables and those framed with dashed line indicates unobserved variables. When atomic bomb radiation is examined to affect mortality among individuals exposed in utero, attained age, sex, city, NIC (whether subjects were in either Hiroshima or Nagasaki City at the time of bombing), and trimester at the time of bombing are examined as factors to describe background mortality and to modify radiation risk of mortality. Small head size, low birth weight and loss of parents as a proxy of complex of family status were assumed to be potential mediators from exposure to atomic bomb radiation to risk of deaths. Several unobserved factors framed with dashed line such as residence, malnutrition, poverty, loss of family (e.g., grandparents, siblings and relatives), mother’s mental stress during pregnancy, lack of medical services, communicable diseases, and inadequate sanitation might affect these three observed factors and mortality