Purposive sampling
Choose cases for their relevance and information value
Purposive sampling deliberately selects cases that can illuminate the question. Criterion sampling applies substantive eligibility requirements; maximum variation sampling seeks contrasts; typical case sampling examines a justified ordinary case. These are related strategies with different purposes, not interchangeable labels. Selection should connect to the intended analysis and may evolve as researchers identify gaps or alternative perspectives.
Use for information-rich qualitative enquiry, implementation research or selecting a qualitative subsample from quantitative results when substantive relevance matters more than estimating population frequencies.
Strengths
- Concentrates effort on cases able to answer the question
- Can deliberately include contrasting or overlooked experiences
Limitations
- Researcher judgements can overlook inconvenient cases
- Selected cases do not give known population inclusion probabilities
Know the boundary
Purposive sampling is not a synonym for recruiting whoever is convenient.