Snowball sampling (also called network, chain referral. or reputational sampling) is a method for sampling (or selecting) the cases in a network. It is based on an analogy to a snowball, which begins small but becomes larger as it is rolled on wet snow and picks up additional snow. Snowball sampling is a multistage technique. It begins with one or a few people or cases and spreads out on the basis of links to the initial cases.