4. Snowball sampling
(Also called network, chain referral, or reputational sampling) is a method for identifying and sampling or selecting the cases in a network. It is based on 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 begin with one or a few people or cases and spreads out on the basis of links to the initial cases.