Sampling: "We argue that sampling is not a procedure that is delegated for locating subjects who represent the population at the beginning of the study, as it is in quantitative inquiry. Rather, in qualitative inquiry, the goal of sampling is to represent the phenomenon...
In qualitative inquiry, first sampling is based on the researcher's need to understand the phenomenon. The researcher's understanding builds incrementally as the study progresses: who is invited to participate in the study (i.e., the sample) is determined by what they know about the topic: that is, what they may contribute – their experience, role, and so forth. As this requisite knowledge changes throughout the study, so does the type of participant who is invited to participate change. In this light, the second difference between quantitative and qualitative sampling is the pacing of the sample...
Later, as the researcher's understanding about the phenomenon increases, participants are selected according to the ‘needs of the study’ or, in grounded theory, the ‘needs of the developing theory’, particularly in developing the concepts and the theoretical properties of the category. This sampling procedure in grounded theory, known as ‘theoretical sampling’ (Glaser, 1978; Strauss, 1987), enables the researcher to purposefully select the sample (according to what data are needed to be explicated or confirmed)."
(Morse & Clark, 2019, "The nuances of grounded theory sampling", SAGE Handbook of Current Developments in Grounded Theory)