Covariate: a variable that is associated with the outcome of interest. For example, in a study of cancer risks, covariates of interest may be age, race/ethnicity, socioeconomic status, smoking status, and others.

Curie (Ci): a special name for the unit of radioactivity equal to 37 billion decays per second.

Decommission: removal of a nuclear facility from service.

Descriptive study: a study concerned with reporting the existing distribution of variables, e.g., cancer registry data analyses that often occur in ecologic studies; contrast to analytical study.

Distribution: the frequency of the values or categories of a measurement made on a population. For example, the age distribution of a population may be summarized as how many people in this population are 0-15, 16-25, 26-45 years of age, and so on.

Dose dose-rate effectiveness factor (DDREF): a factor by which the effect caused by a specific dose or dose rate of radiation changes at low doses or dose rates.

Ecologic fallacy: error in inference associated with ecologic studies due to extrapolating correlations observed at the group level to individuals; e.g., it has been shown that countries with high dietary fat intake have high incidence of breast cancer (the fallacy would be to infer from this observation alone that it is the individuals that have a high fat diet are those that develop breast cancer).

Ecologic study: a study in which the unit of analysis is a population or group (countries, states, counties, communities) and not individuals.

Effluent: solid, liquid, or gaseous release from a nuclear facility.

Epidemiology: the study of the distribution of diseases and other health-related conditions in populations and the application of this study to address health.

Excess risk: an estimate of the amount of risk due to the exposure of interest when the effects of other risk factors are removed. Can be relative or absolute risk.

Experimental study: a study in which the conditions are being directed by the investigator, e.g., a clinical trial in which patients are separated in two groups where some receive a new drug and some receive a placebo.

Follow-up: observation over a period of time of an individual or a population to retrieve new information and record changes in the health status.

Geocoding: the process of finding geographic coordinates (often expressed as latitude and longitude) from other geographic data such as address.

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