representativeness are "The degree to which data accurately and precisely represent the Frequency distribution of a specific variable in the population; a data quality indicator" (QAMS 1993, 20).

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Other /More definition:
Representativeness is a A measure of the degree to which data accurately and precisely characterize a population, parameter variations at a sampling point, a process condition, or a condition; the correspondence between the analytical result and the actual quality or condition experienced by a contaminant receptor.