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demographic information

Personal characteristics of a person or group (e.g., age, sex, race/ethnicity, residence, and occupation) used in descriptive epidemiology to characterize patients or populations. (Adapted from: Centers for Disease Control and Prevention 2014)

descriptive epidemiology

The aspect of epidemiology concerned with organizing and summarizing data regarding the persons affected (e.g., the characteristics of those who became ill), time (e.g., when they become ill), and place (e.g., where they might have been exposed to the cause of illness). (Adapted from: Centers for Disease Control and Prevention 2014)


The phase of petroleum operations that occurs after exploration has proven successful, and before full-scale production. For the purposes of this report, development includes exploration, site preparation, vertical and horizontal drilling, hydraulic fracturing, well completion in preparation for production, and associated waste management. (Source: Schlumberger 2019)

differential misclassification

A type of information bias in which the proportion of subjects misclassified on exposure depends on disease status (case-control studies) or when the proportion of subjects misclassified on disease depends on exposure (cohort studies). (Adapted from: Rothman and Greenland 1998).


Association between an exposure and health outcome that varies in a consistently increasing or decreasing fashion as the amount of exposure (dose) increases. (Adapted from: Centers for Disease Control and Prevention 2014)

drill rig

The machine used to drill a wellbore. (Adapted from: Schlumberger 2019)

drilling cuttings

Fragments of rock dislodged by the drill bit and brought to the surface in the drilling mud. Washed and dried cuttings samples are analyzed by geologists to obtain information about the formations drilled. (Source: U.S. Legal 2019)

drilling mud or drilling fluid

A circulating fluid, one function of which is to lift cuttings out of the wellbore and to the surface. It also serves to cool the bit and to counteract downhole formation pressure. (Source: OSHA 2001)