Can sample size in qualitative research be determined a priori?

Abstract

There has been considerable recent interest in methods of determining sample size for qualitative research a priori, rather than through an adaptive approach such as saturation. Extending previous literature in this area, we identify four distinct approaches to determining sample size in this way: rules of thumb, conceptual models, numerical guidelines derived from empirical studies, and statistical formulae. Through critical discussion of these approaches, we argue that each embodies one or more questionable philosophical or methodological assumptions, namely: a naïve realist ontology; a focus on themes as enumerable 'instances', rather than in more conceptual terms; an incompatibility with an inductive approach to analysis; inappropriate statistical assumptions in the use of formulae; and an unwarranted assumption of generality across qualitative methods. We conclude that, whilst meeting certain practical demands, determining qualitative sample size a priori is an inherently problematic approach, especially in more interpretive models of qualitative research.

Rapid risk assessment for communicable diseases in humanitarian emergencies: validation of a rapid risk assessment tool for communicable disease risk in humanitarian emergencies

“…We interviewed 25 people. We did not determine the study size a priori as we agree with Sim et al (28) that a priori determination of the sample size for qualitative key-informant interviews is wrought with problematic issues due to the underlying "questionable philosophical and/or methodological assumptions". We reached saturation after 20 interviews and conducted another five interviews to confirm.…”

‘There’s more to life than money and health’: Family caregivers’ views on the role of Power of Attorney in proxy decisions about research participation for people living with dementia

“…Adequacy of sample size can be determined through the number of events, incidents and experiences explored, rather than solely in terms of the number of participants (Sandelowski, 1995). Data collection continued until data saturation was considered to have been reached (Sim, Saunders, Waterfield, & Kingstone, 2018). The interviews were digitally audio-recorded with consent, transcribed verbatim by a professional transcription service provider, and anonymised.…”

Customer Services and Its Efficiency Level of 3rd Party Logistics Companies

“…The final rubric then tested by four experts in logistics services personnel with more than five years of working experiences in international 3PL operations. The companies refused to be named due to the competitive and private confidential issues, which were later categorized as Company A, Company B, Company C and Company D. The determination of sample size for exploratory research strongly argued among scholars however, the sample size should be allocated according to the research objectives, demographic and depth of the case study [36]. According to [37], one respondent with appropriate criteria is adequate for exploratory research and are referred to in the current study.…”