Interview and Sampling: How Many and Whom

Sample Size

The early development of qualitative research followed quantitative research in that there were attempts to establish numerical requirements for the selection of participants. There were two challenges in this approach. The first was that qualitative theorists could not agree on an optimal sample size. Researchers have discussed a range of numbers for samples in phenomenological studies. Thomas and Pollio (2002) suggest that an appropriate sample size for phenomenological research [Page 244]can range from 6 to 12 participants—provided there is thematic redundancy after hearing the narratives of 6 participants. Creswell (1998) recommended between 5 and 25 participants, with another researcher (Boyd, 2001) prescribing a more flexible range of 2 to 10. These differences extend to other common qualitative approaches, such as grounded theory, and make it difficult for qualitative researchers to predetermine a sample size.

Theoretical saturation is becoming the most common approach to sample size. Guest et al. (2006) write, “Saturation has, in fact, become the gold standard by which purposive sample sizes are determined in health science research” (p. 60). The authors go on to point out that theoretical saturation is not without its own deficiencies. The main flaw is the lack of a common description of how saturation is reached. This shortcoming especially affects the advancement of qualitative methodology. Particularly, researchers with little qualitative experience and funding applicants who need to establish and justify their budgets are more likely to follow the quantifiable approach and identify sample sizes in their proposals (Cheek, 2000). Since grant funders continue to favor quantitative designs over qualitative designs (Morse, 2003), qualitative researchers are pressured to identify a preestablished sample size to navigate the politics of grant funding. With vague guidelines on the use of saturation, a priori sample sizes will remain a part of qualitative research and reinforce the mind-set that the quality and validity of qualitative research should be measured with quantitative criteria.

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