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Non-Probability Sampling

👥 Sociology By CampusDown Wiki Editorial Team Last updated
Quick answer: In non-probability sampling the chance of selecting each population element is unknown; convenience, purposive, quota and snowball sampling are cheap and quick but cannot support statistical generalisation.
Contents
  1. 1. Versus probability sampling
  2. 2. Types
  3. 3. When to use
  4. 4. References

Versus probability sampling

Probability sampling uses random selection with known probabilities, allowing sampling error and confidence intervals. Non-probability methods rely on judgement or accessibility, risking selection bias and preventing error estimation.

Types

  • Convenience: whoever is readily available, e.g. students in a class.
  • Purposive (judgement): cases chosen for the information they can provide.
  • Quota: quotas matching population proportions on traits such as sex and age, filled non-randomly.
  • Snowball: participants refer others; used for hidden populations, with respondent-driven sampling as a refined version.

When to use

Exploratory and pilot studies, qualitative research and populations without a sampling frame. The Literary Digest's wrong 1936 US election forecast from a huge but biased sample shows selection method matters more than size.

References

  1. Babbie, E. (2021). The Practice of Social Research (15th ed.). Cengage.
  2. Patton, M. Q. (2015). Qualitative Research and Evaluation Methods (4th ed.). Sage.
  3. Heckathorn, D. D. (1997). Respondent-driven sampling: A new approach to the study of hidden populations. Social Problems, 44(2), 174-199.
  4. Squire, P. (1988). Why the 1936 Literary Digest poll failed. Public Opinion Quarterly, 52(1), 125-133.

Reports and materials that use this theory (Korean)

There are no materials dedicated to this theory yet, but you can search related reports in the CampusDown library (Korean).

Find more reports · Search '비확률표집' on CampusDown →
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This article was last updated on October 15, 2026. It is based on widely recognized original works and textbooks; when citing it in a paper, please check the original sources listed in the references.