Qualitative and quantitative research designs require the researcher to think carefully about how and how many to sample within the population segment(s) of interest related to the research objectives. In doing so, the researcher considers demographic and cultural diversity, as well as other distinguishing characteristics (e.g., usage of a particular service or product) and pragmatic issues (e.g., access and resources). In qualitative research, the number of events (i.e., the number of in-depth interviews, focus group discussions, or observations) and participants is often considered at the early design stage of the research and then again during the field stage (i.e., when the interviews, discussions, or observations are being conducted). This two-stage approach, however, can be problematic. One reason is that giving an accurate sample size prior to data collection can be difficult, particularly when the researcher expects the number to change as the result of in-the-field decisions.
Another potential problem arises when researchers rely solely on the concept of saturation to assess sample size when in the field. In grounded theory, theoretical saturation
“refers to the point at which gathering more data about a theoretical category reveals no new properties nor yields any further theoretical insights about the emerging grounded theory.” (Charmaz, 2014, p. 345)
In the broader sense, Morse (1995) defines saturation as “‘data adequacy’ [or] collecting data until no new information is obtained” (p. 147).
Reliance on the concept of saturation presents two overarching concerns: 1) As discussed in two earlier articles in Research Design Review – Beyond Saturation: Using Data Quality Indicators to Determine the Number of Focus Groups to Conduct and Designing a Quality In-depth Interview Study: How Many Interviews Are Enough? – the emphasis on saturation has the potential to obscure other important considerations in qualitative research design such as data quality; and 2) Saturation as an assessment tool potentially leads the researcher to focus on the obvious “new information” obtained by each interview, group discussion, or observation rather than gaining a deeper sense of participants’ contextual meaning and more profound understanding of the research question. As Morse (1995) states,
“Richness of data is derived from detailed description, not the number of times something is stated…It is often the infrequent gem that puts other data into perspective, that becomes the central key to understanding the data and for developing the model. It is the implicit that is interesting.” (p. 148)
With this as a backdrop, a couple of recent articles on saturation come to mind. In “A Simple Method to Assess and Report Thematic Saturation in Qualitative Research” (Guest, Namey, & Chen, 2020), the authors present a novel approach to assessing sample size in the in-depth interview method that can be applied during or after data collection. This approach is born from Read Full Text