|P.Mean: Justifying the sample size in a qualitative research study (created 2011-11-22).
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I was asked to help justify the sample size for a qualitative research study. When the goals of a study are qualitative, the sample size justification is also qualitative.
Qualitative studies have a level of flexibility that would cause trouble for a quantitative study and you need to get comfortable with this flexibility. Frequently sampling is done on an ongoing basis and the sampling strategy is often modified as the qualitative summaries of the early results occur. You might change the size, location, and composition of your focus groups for example, to try to explore more efficiently some of the provisional findings from the earlier focus groups. In a study of nursing work environment, for example, there was a large, vocal, and unexpected commentary about generational differences between nurses. This led to formation of new focus groups with only Baby Boomer nurses and only Generation X nurses. Sampling typically ends in a qualitative study when saturation occurs. Saturation is when you start hearing the same themes over and over again and no new themes are emerging.
That's all well and good, but you have to submit a grant and the budget for the grant before any qualitative research is done. What you have to do is to rely on sample sizes used in similar qualitative studies, project a reasonable upper bound, and then say that sampling will continue until saturation occurs or the upper bound is reached. You might want to also toss in something along the lines of "the sampling approach will be modified if the upper bound for sample size is being approached without any evidence of convergence of themes."
This page was written by Steve Simon and is licensed under the Creative Commons Attribution 3.0 United States License. Need more information? I have a page with general help resources. You can also browse for pages similar to this one at Qualitative Data.