Glossary

An instance of a particular disease, injury, or other health condition that meets selected criteria. (Adapted from: Centers for Disease Control and Prevention 2014)

An observational analytic study that enrolls one group of persons with a certain disease, chronic condition, or type of injury (case-patients) and a group of persons without the health problem (control subjects) and compares differences in exposures, behaviors, and other characteristics to identify and quantify associations, test hypotheses, and identify causes. (Adapted from: Centers for Disease Control and Prevention 2014)

Heavy steel pipe placed in an open hole and cemented into place. Casing is designed to withstand high pressures, large tensile loads, and resist chemical reaction and corrosion. A casing string refers to a series of connected segments of casing or pipe that serves to prevent the hole from caving, keep the fluids inside the casing string from migrating to porous formations, prevent unwanted fluids from entering the hole, and protect freshwater aquifers. (Source: Michigan Department of Environmental Quality 2013)

The geographic locations served by an institution, such as a hospital. (Adapted from: Centers for Disease Control and Prevention 2014) 

To prepare and pump cement into place in a wellbore. Cementing operations may be undertaken to seal the annulus after a casing string has been run, to seal a lost circulation zone, to set a plug in an existing well from which to push off with directional tools or to plug a well so that it may be abandoned. (Source: Schlumberger 2019)

An experimental study that uses data from individual persons. The investigator specifies the type of exposure for each study participant and then follows each person's health status to determine the effects of the exposure. (Adapted from: Centers for Disease Control and Prevention 2014)

A well-defined group of persons who have had a common experience or exposure and are then followed up, as in a cohort study or prospective study, to determine the incidence of new diseases or health events. (Adapted from: Centers for Disease Control and Prevention 2014)

An observational analytic study in which enrollment is based on the status of exposure to a certain factor or membership in a certain group. Populations are followed, and disease, death, or other health-related outcomes are documented and compared. Cohort studies can be either prospective or retrospective. (Adapted from: Centers for Disease Control and Prevention 2014)

A group in an analytical study (e.g., a cohort or case-control study) with whom the primary group of interest (exposed group in a cohort study or case-patients in a case-control study) is compared. The comparison group provides an estimate of the background or expected incidence of disease (in a cohort study) or exposure (in a case-control study). (Adapted from: Centers for Disease Control and Prevention 2014)

A generic term used to describe the events and equipment necessary to bring a wellbore into production once drilling operations have been concluded, including but not limited to the assembly of downhole tubulars and equipment required to enable safe and efficient production from an oil or gas well. (Source: Schlumberger 2019)

Any combination of facilities that supply the energy to move gas in transmission or distribution lines or into storage by increasing the pressure. Compressor stations might include equipment to remove liquids, particles, and other impurities from the natural gas, which are disposed of or sold as desired. (Source: U.S. Energy Information Administration 2019)

Identifying sources of exposure, how the contaminant behaves in the environment, and the context in which people come into contact with the contaminant that results in an adverse health effect. (Adapted from: Boston University School of Public Health 2016)

A range of values for a measure (e.g., rate or odds ratio) constructed so that the range has a specified probability (often, but not necessarily, 95%) of including the true value of the measure. (Adapted from: Centers for Disease Control and Prevention 2014)

A factor that distorts the association between an exposure and a health outcome that is related to both. (Adapted from: Centers for Disease Control and Prevention 2014)

The distortion of the association between an exposure and a health outcome by a third variable that is related to both. (Adapted from: Centers for Disease Control and Prevention 2014)

In a case-control study, a member of the group of persons without the health problem under study (see also comparison group and case-control study). (Adapted from: Centers for Disease Control and Prevention 2014)

Crude oil and natural gas that is produced by a well drilled into a geologic formation in which the reservoir and fluid characteristics permit the oil and natural gas to readily flow to the wellbore. (Source: U.S. Energy Information Administration 2019)

A study in which a sample of persons from a population are enrolled and their exposures and health outcomes are measured simultaneously; a survey. (Adapted from: Centers for Disease Control and Prevention 2014)

When referring to a rate, an overall or summary rate for a population, without adjustment. (Adapted from: Centers for Disease Control and Prevention 2014)