CHIME News

Publication: Supporting thinking on sample sizes for thematic analyses: a quantitative tool

13 February 2015

A new paper by Andy Fugard (UCL Clinical, Educational & Health Psychology) and Henry Potts (UCL CHIME) offers a tool to support thinking on sample sizes for interview studies.

The question of how many people to recruit in a qualitative study is still largely unanswered, with wide variations in recommendations given in the literature. Sampling until saturation is often used, but this approach cannot be employed prospectively. When it comes to planning a study, seeking resources, or going through ethics and governance procedures, researchers would benefit from being better able to estimate how many participants are needed.

Power calculations are well-established in quantitative studies, but they do not immediately seem applicable to qualitative studies that don’t use statistical analysis. However, Fugard & Potts propose a statistical approach to inform sample size decisions for studies using thematic analysis. Users need to think about what is the least prevalent theme they would be interested in discovering. The results can then be used as part of a wider consideration of what number would be appropriate for a study.

The paper - Fugard, A. J. B. & Potts, H. W. W. (2015). Supporting thinking on sample sizes for thematic analyses: A quantitative tool - appears in the International Journal of Social Research Methodology along with commentaries by Hammersley, Emmel and Byrne and a response from the authors, which reveals that the approach is already proving controversial.

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