Multi-layered sampling strategy for qualitative interviews: methodical reflections on sampling interviews with the European Research Council review experts

Interviews are one of the primary methods of collecting empirical data in qualitative research. Given their significance, various aspects of interviewing have undergone methodological scrutiny by scholars aiming to refine the method and enhance its effectiveness. This article reflects on the process of selecting informants for expert interviews and proposes a systematic approach to sampling informants for expert and elite interviews. Specifically, we outline the process of selecting a subset of interviewees from a group of over 1,200 experts. Crucially, each individual in this population is identifiable by name, and there are discernible, meaningful differences among them that are visible to the researchers. Under these conditions, we propose a reflexive and systematic approach to stratified random sampling to diminish potential biases. This multi-layered sampling strategy not only minimises bias but also offers insights into the overall structure of the population of experts, providing essential contextual knowledge for analysis.