A sample which accurately reflects a specific condition or set of conditions within the universe.
research subjects with essentially the same distribution of analytically relevant characteristics as the population/group/segment from which it was drawn. The representativeness enables the analysis to give a reasonably accurate portrayal of the research subject's characteristics and known diversity.
A sample that consists of a number of units that are drawn based on rational criteria such as random sampling and intended to assure that the sample accurately portrays the material being sampled. [From §210.3(b)(21)