Snowball Sampling
Methodology & design
Non-probability sampling in which existing participants refer further participants — the standard route into hard-to-reach or networked populations.
Snowball sampling recruits initial participants who then refer others from their networks, with each wave generating the next. It is a non-probability technique used when the population is hidden, hard to reach or lacks any sampling frame — informal traders, undocumented workers, specialists in a small professional niche.
Its strength is access. Referral from a trusted peer confers credibility the researcher could not obtain directly, which is often the only realistic route into closed or stigmatised populations.
Its weakness is selection bias: because recruitment follows social networks, well-connected individuals are over-represented and isolated members of the population may never be reached, so the sample cannot claim representativeness. Mitigate it by starting from several unconnected seeds, and report the number of seeds, the chain lengths and the resulting limitation honestly.
Where it's used
- Reaching populations without a sampling frame (e.g. gig workers, migrants)
- Building expert samples through professional referral chains
Related concepts
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