Characterising and justifying sample size sufficiency in interview-based studies: systematic analysis of qualitative health research over a 15-year period
By Konstantina Vasileiou, Julie Barnett, S. Thorpe, Terry Young. BMC Medical Research Methodology, 2018
2,611 citations recorded by the source corpus.
BackgroundChoosing a suitable sample size in qualitative research is an area of conceptual debate and practical uncertainty. That sample size principles, guidelines and tools have been developed to enable researchers to set, and justify the acceptability of, their sample size is an indication that the issue constitutes an important marker of the quality of qualitative research. Nevertheless, research shows that sample size sufficiency reporting is often poor, if not absent, across a range of disciplinary fields.MethodsA systematic analysis of single-interview-per-participant designs within three health-related journals from the disciplines of psychology, sociology and medicine, over a 15-year period, was conducted to examine whether and how sample sizes were justified and how sample size was characterised and discussed by authors. Data pertinent to sample size were extracted and analysed using qualitative and quantitative analytic techniques.ResultsOur findings demonstrate that provision of sample size justifications in qualitative health research is limited; is not contingent on the number of interviews; and relates to the journal of publication. Defence of sample size was most frequently supported across all three journals with reference to the principle of saturation and to pragmatic considerations. Qualitative sample sizes were predominantly – and often without justification – characterised as insufficient (i.e., ‘small’) and discussed in the context of study limitations. Sample size insufficiency was seen to threaten the validity and generalizability of studies’ results, with the latter being frequently conceived in nomothetic terms.ConclusionsWe recommend, firstly, that qualitative health researchers be more transparent about evaluations of their sample size sufficiency, situating these within broader and more encompassing assessments of data adequacy. Secondly, we invite researchers critically to consider how saturation parameters found in prior methodological studies and sample size community norms might best inform, and apply to, their own project and encourage that data adequacy is best appraised with reference to features that are intrinsic to the study at hand. Finally, those reviewing papers have a vital role in supporting and encouraging transparent study-specific reporting.
Subfields: Sociology and Political Science, Statistics and Probability
View Paper: https://www.semanticscholar.org/paper/f56ba79dc59216502b92a55560006ef57e8026b8
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Citations in the corpus
- DETERMINING THE SAMPLE SIZE IN QUALITATIVE RESEARCH (2020, background): “According to Vasileiou et al. (2018), its appropriateness is expressed by the composition’s appropriateness (cases, units rich in information) and sample size (proper data for fully explaining the occurrence – quantity, quality).”
- ‘Define, Explain, Justify, Apply’ (DEJA): An analytic tool for guiding qualitative research sample size (2021, background): “such as passing the muster of institutional ethics committees and funding agencies (Fugard & Potts, 2015a; Kindsiko & Poltimäe, 2019; Sim et al., 2018a; Vasileiou et al., 2018).”
- Student fears of oral presentations and public speaking in higher education: a qualitative survey (2021, methodology): “The saturation of data was used to indicate the optimal sample size for this qualitative survey as this is the most widely used principle for determining sample size and evaluating its sufficiency (Vasileiou et al. 2018) The UWE Faculty Research Ethics Committee reviewed and approved this study.”