Hyperlink 10. Representativeness, Averages, and Populations

The term “representative” as used in this document has been previously defined. However, the term has been used in a variety of ways in other guidance documents. For example, other guidance has linked the concept of representativeness to a mean for a population (the “universe or whole”) of interest. According to the Resource Conservation and Recovery Act (RCRA), a representative sample is defined in terms of an average: “Representative sample means a sample of a universe or whole (e.g., waste pile, lagoon, ground water) which can be expected to exhibit the average properties of the universe or the whole” (Title 40 Code of Federal Regulations Part 260.10 [40 CFR §260.10]). In addition, the ASTM International (ASTM) Standard D 6044-96 defines a representative sample as “a sample collected in such a manner that it reflects one or more characteristics of interest (as defined by the project objectives) of a population from which it was collected” (ASTM 2009). Although it is nearly impossible for a single discrete soil sample to fulfill this expectation, an ISM sample, which more closely resembles a statistical sample, can.

A vital prerequisite for developing a sampling design is to unambiguously define the “population” and the characteristics of interest to be targeted by the decision-making process. A “population” is the entire set or total membership of entities that display some characteristic of interest. For soils, the population of interest is defined by location, spatial dimensions, and characteristics such as particle size. The population is the “whole” from which samples are taken to measure properties of interest. The population is what the samples are to represent.