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P value

The probability of observing an association between two variables or a difference between two or more groups as large or larger than that observed if the null hypothesis were true. Used in statistical testing to evaluate the plausibility of the null hypothesis (i.e., whether the observed association or difference plausibly might have occurred by chance). (Adapted from: Centers for Disease Control and Prevention 2014)

particulate matter (PM)

A small, discrete mass of solid or liquid matter that remains individually dispersed in gas or liquid emissions. Particulates take the form of aerosol, dust, fume, mist, smoke, or spray. Each of these forms has different properties. (Source: U.S. Energy Information Administration 2019)


To pierce the casing wall and cement to provide holes through which formation fluids may enter or to provide holes in the casing so that material may be introduced into the annulus between the casing and the wall of the borehole. Perforating is accomplished by lowering into the well a perforating gun, or perforator, that fires bullet-shaped charges that are electrically detonated from the surface. (Source: OSHA 2001)


A measure of the ease with which fluids can flow through a porous rock. (Source: OSHA 2001)


An area in which hydrocarbon accumulations or prospects of a given type occur. The shale gas plays in North America, for example, include the Barnett, Eagle Ford, Fayetteville, Haynesville, Marcellus, and Woodford, among many others. (Source: Schlumberger 2019)


The total number of inhabitants of a geographic area or the total number of persons in a particular group (e.g., the number of persons engaged in a certain occupation). (Adapted from: Centers for Disease Control and Prevention 2014)

potable water

Water suitable for drinking. (Source: Water Education Foundation 2019)


The reduction of random error in measurement and estimation. (Adapted from: Rothman and Greenland 1998)


The number or proportion of cases or events or attributes among a given population. (Adapted from: Centers for Disease Control and Prevention 2014)

prevalence rate

The proportion of a population that has a particular disease, injury, other health condition, or attribute at a specified point in time (point prevalence) or during a specified period (period prevalence). (Adapted from: Centers for Disease Control and Prevention 2014)

prevalent cases

Study participants in which the outcome occurs before selection for or enrollment into the study. (Adapted from: Rothman and Greenland 1998)

produced water

Water produced from a wellbore that is not a treatment fluid. The characteristics of produced water vary and use of the term often implies an inexact or unknown composition. It is generally accepted that water within the pores of shale reservoirs is not produced due to its low relative permeability and its mobility being lower than that of gas. (Source: Schlumberger 2019)


The phase of the petroleum industry that deals with bringing the well fluids to the surface and separating them as well as with storing, gauging, and otherwise preparing the product for distribution. For the purposes of HEI-Energy, production includes extraction, gathering, processing, and compression of gas; extraction and processing of oil and natural gas condensates; management of produced water and other wastes; and operation of gathering pipelines. (Source: OSHA 2001)

production casing

The last string of casing or liner that is set in a well, inside of which is usually suspended the tubing string. (Source: OSHA 2001)


A granular substance (silica sand, aluminum pellets, or other material) that is carried in suspension by the fracturing fluid and serves to keep the cracks open when fracturing fluid is withdrawn after a fracture treatment. (Source: International Association of Drilling Contractors 2019)

prospective study

An analytical study in which participants are enrolled before the health outcome of interest has occurred. (Adapted from: Centers for Disease Control and Prevention 2014)