Characterising and justifying sample size sufficiency in interview-based studies

Systematic analysis of qualitative health research over a 15-year period

Bibliographic Data

ID23313433
AuthorsKonstantina Vasileiou (0000-0001-5047-3920, University of Bath, corresponding author), Julie Barnett (0000-0001-5740-0863, University of Bath), Susan Thorpe, Susan J Thorpe (Newcastle University), Terry Young (0000-0001-9545-2269, Brunel University of London)
Year2018
Volume18
Issue1
Pages148-148
Publication date2018-12-01
Peer ReviewedYes
Open AccessYes
TypeARTICLE
VenueBMC Medical Research Methodology (JOURNAL)
Journal identifiersISSN: 1471-2288 • E-ISSN: 1471-2288
PublisherSpringer Science and Business Media LLC (PUBLISHER)
DOI10.1186/s12874-018-0594-7
PMID30463515
OpenAlexW2900619723
LanguageEN
Citations received562
References cited54

BACKGROUND: Choosing 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. METHODS: A 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. RESULTS: Our 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. CONCLUSIONS: We 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.

Context (archaeology) · Developmental psychology · External validity · Generalizability theory · Geography · Qualitative research · Research design · Sample (material) · Sample size determination · Social science · Sociology · Statistics · Applied Psychology · Focus Groups and Qualitative Methods · Mathematics · Meta-analysis and systematic reviews · Psychology · Reliability and Agreement in Measurement · Social Psychology