Purposive Sampling
Participants selected based on specific pre-defined criteria directly relevant to the research questions. NOT the same as convenience sampling — requires explicit, theoretically-grounded inclusion criteria. The most defensible non-probability strategy. Cite Patton (2015) who identifies 16 types.
✓ Criterion Sampling✓ Maximum Variation✓ Typical Case✓ Snowball✓ Theoretical Sampling
Total Population / Census Sampling
All members of a small, accessible population are included. Used when the population is small enough (typically n ≤ 200) that sampling is unnecessary. Strong justification: no sampling error. Cite Slovin's Formula as a reference point for when sampling becomes necessary.
Snowball Sampling
Initial participants recruit additional participants from their networks. Used when the population is hard to reach or hidden (e.g., people with rare conditions, underground workers). Limitations: non-representative, biased toward researcher's network; justify with population inaccessibility.
⚠ Convenience Sampling — Use with Caution
Selection based solely on availability and accessibility with no theoretical inclusion criteria. Weakest sampling strategy — significantly limits generalizability. If used, state explicitly that findings are limited to the accessible sample and are not generalizable beyond the study context.