1. The dose that produces a specific effect; when followed by a subscript (generally “ED50”), it denotes the dose having such an effect on a certain percentage (50%) of the test animals; ED50 is the median effective dose. 2. In radiation protection, the sum of the equivalent doses in all tissues and organs of the body weighted for tissue effects of radiation. The SI unit of effective dose is the sievert (Sv) (=100 rem). 3. in diagnostic radiology, if a patient weighing W absorbs A joules of energy, and the experimentally derived ratio of effective dose to energy absorbed in an anthropomorphic phantom with mass M is R, then the effective dose is A·R·M:W. This formula results in a larger value for children despite their lesser absorption of radiation.