purposive sample

n. a portion, within a body of records, selected for permanent retention because it meets criteria for selection set by the appraisal archivist; a subjective sample

Notes

A purposive sample has no random element to it. Instead, the archivist sets criteria that are characteristics of important records and then compares each file to those criteria to decide which records are retained. The purposive sample is not statistically valid, so it is used with relatively heterogeneous records as a way of separating the archival wheat from the nonpermanent chaff.