Sampling in Qualitative Research: Insights from an Overview of the Methods Literature

Merriam-Webster Dictionary defines sampling as "the act, process, or technique of selecting a representative part of a population for the purpose of determining parameters or characteristics of the whole population. " This popular understanding, however, differs from some of the understandings held by researchers and scholars in the qualitative research domain. Influential qualitative methods authorities from diverse backgrounds have contributed to these latter understandings, and there is much natural variation in the sampling-related ideas they present. The existence of even subtle inconsistencies, ambiguities, or incomplete descriptions in the methods literature regarding certain sampling-related issues can be problematic for students and researchers seeking to develop a coherent understanding of sampling that is applicable to their research situation. This problem can be exacerbated by the fact that these individuals often lack the time to search, retrieve, and review the qualitative methods literature systematically and exhaustively to develop comprehensive and balanced knowledge of the available methods guidance. Even seasoned qualitative researchers, who are usually expertly versed in the methods of their chosen research approach or tradition, may come to prefer and become most intimately familiar with the ideas of a subset of methods authors within that tradition. Thus, they may not be comprehensively familiar with the full range of opinions across authors (including any inconsistencies among them) within their tradition regarding a specific methods issue --something that can only be revealed through systematic comparison. Systematic comparison in turn depends on systematic selection of the literature to be compared. Systematically searching and selecting the methods literature, however, is generally more burdensome than it is for the empirical findings literature. This is because a greater proportion of the methods literature is found in books and edited book chapters, which take substantially more time and effort to identify, retrieve, and scan for relevant content compared to journal articles. To fill the need for rigorous synthesis of the guidance on sampling in qualitative research, we conducted a systematic methods overview--our term for a defined approach to reviewing the methods literature from diverse sources, described here. This review method involved a rigorous and transparent, yet purposeful, approach to searching the methods literature aimed at selecting and reviewing the most influential publications--ones that students and researchers from multiple jurisdictions are most likely to encounter among the available writings that address sampling. We chose the literature of grounded theory, phenomenology, and case study because these are popular approaches or traditions used in many health-related disciplines, and are also sufficiently different to allow instructive comparisons to be made within each of the sampling topics addressed below. Our findings are organized under eight distinct topic sections corresponding to the major domains of sampling identified in the review process. In each section, we summarize how the topic is characterized in the literature reviewed, present a comparative analysis of differences among the three research traditions, and finally offer comments representing our analysis of the clarity, consistency and comprehensiveness of the available guidance from the authors reviewed on that topic and potential areas in which more clarity could be provided. Importantly, it is neither our aim nor our intention to convey personal opinions or recommendations about how to do sampling in this review. By unifying the findings and discussion within topic sections, we aim to make it convenient for readers to locate content for any single sampling topic in one place. The Three Research Traditions Reviewed Each of the three traditions whose methods literatures were reviewed is characterized by its unique approach to data collection and analysis, which in turn underlies important variation in researchers' approaches and attention to sampling. …