systematic sample

n. a portion, within a body of records, selected for permanent retention through a process that employs a preset pattern of selection to produce a subset of the whole; a systematic random sample


Systematic sampling replaces true randomness with a systematized pattern of selection that is easier to implement and relatively, though not actually, random. Systematic sampling is conducted in cases, for instance, where random numbers cannot be generated to match case numbers because no case numbers exist. In such cases, a simple pattern, such as choosing each tenth file for retention, is used to imitate randomness.