Sample Size in Qualitative Interview Studies

TLDR

Qualitative studies require sample size determination, yet the prevailing concept of saturation is method‑specific and inconsistently applied. The study proposes the concept of information power to guide adequate sample size in qualitative research. Information power posits that a sample with more relevant information requires fewer participants, and the authors present a model linking study aim, sample specificity, theory use, dialogue quality, and analysis strategy to information power. The authors discuss applying the model during study planning and data collection.

Abstract

Sample sizes must be ascertained in qualitative studies like in quantitative studies but not by the same means. The prevailing concept for sample size in qualitative studies is “saturation.” Saturation is closely tied to a specific methodology, and the term is inconsistently applied. We propose the concept “information power” to guide adequate sample size for qualitative studies. Information power indicates that the more information the sample holds, relevant for the actual study, the lower amount of participants is needed. We suggest that the size of a sample with sufficient information power depends on (a) the aim of the study, (b) sample specificity, (c) use of established theory, (d) quality of dialogue, and (e) analysis strategy. We present a model where these elements of information and their relevant dimensions are related to information power. Application of this model in the planning and during data collection of a qualitative study is discussed.