snowball sample
n.— «Researchers pursue what is called a “snowball sample,” seeking out workers who then recruit their friends in a process they liken to a chain letter, or to the “six degrees of separation” theory of connectedness. A mathematical formula is applied to the sample like a “corrective lens,” Professor Heckathorn explained, to obtain a sample that is “theoretically independent of its nonrandom starting points.”» —“In Challenge to Survey Low-Wage Workers, Researchers Pursue ’Snowball Sample'” by Sam Roberts New York Times Apr. 15, 2006. (source: Double-Tongued Dictionary)
Further reading
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