Sampling in Qualitative and Quantitative Research
1. General Considerations for Sample Size in Qualitative Research
- No strict rules: Sample size in qualitative research depends on the research purpose and the amount of data needed (Roller & Lavrakas, 2015).
- Justification required: Researchers must provide a rationale for their sample size.
- Variation in sample size:
- A single case may suffice for projects like oral history or autoethnography.
- 20+ participants may be needed for focus group studies.
- Guidelines for interviews:
- No rigid rules; sample size should be planned upfront.
- Kvale & Brinkmann (2008): "Interview as many subjects as necessary to find out what you need to know."
2. Sampling Strategies
All sampling methods fall under two broad categories: Probability Sampling and Non-Probability Sampling.
A. Probability Sampling
- Simple Random Sampling (SRS): Every element has an equal chance of selection.
- Systematic Random Sampling: First element is randomly selected, then every k-th element is chosen.
- Cluster Sampling: Uses pre-existing clusters (e.g., universities) and involves a two-stage selection process.
- Stratified Random Sampling: Population divided into strata based on shared characteristics.
B. Non-Probability Sampling
- Purposeful Sampling (Purposive/Judgment Sampling): Focuses on "information-rich cases."
- Snowball Sampling (Chain Sampling): One participant leads to another.
- Exemplar of the Phenomenon of Interest: Selection of a single significant case providing rich data.
- Homogeneous Sampling: Participants share a common characteristic.
- Accidental Sampling: Selection based on convenience.
- Quota Sampling: Ensures representation of diverse elements in the population.
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