Glossary

A sample of persons chosen in such a way that each one has the same (and known) probability of being selected. (Adapted from: Centers for Disease Control and Prevention 2014)

An expression of the relative frequency with which an event occurs among a defined population per unit of time, calculated as the number of new cases or deaths during a specified period divided by either person-time or the average (midinterval) population. In epidemiology, it is often used more casually to refer to proportions that are not truly rates (e.g., attack rate or case-fatality rate). (Adapted from: Centers for Disease Control and Prevention 2014)

A measure of association that quantifies the relation between an exposure and a health outcome from an epidemiological study, calculated as the ratio of incidence rates or mortality rates of two groups. (Adapted from: Centers for Disease Control and Prevention 2014)

Systematic differences in the way subjects remember or report exposures or outcomes (a type of information bias). (Adapted from: Rothman and Greenland 1998)

Process of restoring surface environment to acceptable pre-existing conditions. Includes surface contouring, equipment removal, well plugging, revegetation, and other processes. (Source: U.S. Energy Information Administration 2019)

A general term for measures of association calculated from the data in a two-by-two table, including risk ratio, rate ratio, and odds ratio (see also risk ratio). (Adapted from: Centers for Disease Control and Prevention 2014)

A sample whose characteristics correspond to those of the original or reference population. (Adapted from: Centers for Disease Control and Prevention 2014)

A subsurface, porous, permeable rock body in which oil or gas or both are stored. Most reservoir rocks are limestones, dolomites, sandstones, or a combination of these. The three basic types of hydrocarbon reservoirs are oil, gas, and condensate. (Available: Aspen Environmental Group 2015)

Can occur when factors related to both the exposure and outcome of interest (i.e., confounders) are not controlled for in statistical analyses or are controlled but measured inaccurately. (Adapted from: Centers for Disease Control and Prevention 2014)

An analytical study in which participants are enrolled after the health outcome of interest has occurred. Case-control studies are inherently retrospective. (Adapted from: Centers for Disease Control and Prevention)

The probability that an event will occur (e.g., that a person will be affected by, or die from, an illness, injury, or other health condition within a specified time or age span). (Adapted from: Centers for Disease Control and Prevention 2014)

An aspect of personal behavior or lifestyle, an environmental exposure, or a hereditary characteristic that is associated with an increase in the occurrence of a particular disease, injury, or other health condition.

A measure of association that quantifies the association between an exposure and a health outcome from an epidemiological study, calculated as the ratio of incidence proportions of two groups. (Adapted from: Centers for Disease Control and Prevention 2014)