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## E

EAR.

See excess risk.

ERR.

See excess risk.

Excess risk.

Risk, whether it is relative or absolute, is often expressed in terms of the excess that it represents over expectations in the absence of exposure to a carcinogenic agent, radiation in this instance. Excess relative risk (ERR) is, therefore, merely the observed relative risk minus 1, the value expected in the absence of an effect of radiation. Similarly excess absolute risk (EAR) is the number of incident cases or deaths at a particular dose above the number that would be expected in the absence of a radiation-related increase.

Exposure

Technically, exposure is the amount of air ionized by radiant energy, specifically, the amount of electrical charge produced in 1 cc of air under condition of electron equilibrium. More commonly, and in the present context, it simply means the presence of an individual in a field of radiation.

## G

Geometric mean (abbreviated GM).

The geometric average of a series of n positive numbers; it is equal to the nth root of their product. As an illustration, the geometric mean of the numbers 2 and 8 is the square root of 16 (their product) or 4. The GM is approximately the median (50th percentile) of a distribution of numbers whose logarithms are normally distributed.

Geometric standard deviation (abbreviated GSD).

The geometric standard deviation is the antilog of the standard deviation of the natural logarithms of a set of numbers. The GSD is usually used to describe the variation of a set of data that is positively skewed.

GM.

See geometric mean.

Gray (abbreviated Gy).

The SI unit of absorbed dose equal to 1 joule per kilogram, or 100 rad. The unit derives its name from the English biophysicist Louis Harold Gray.

GSD.

See geometric standard deviation.

Gy.

See Gray.

## K

Kriging.

Kriging is defined as the process of estimating the value of a spatially distributed variable from adjacent values while considering their interdependence.

## P

Probability of causation.

A number that expresses the probability that a given cancer, in a specific tissue has been caused by a previous exposure to a carcinogenic agent, such as ionizing radiation.