Purposive and theoretical sampling
because there is always a limit to how many respondents we can contract or how many sites we can visits, we have to make some principled decisions on how to select our respondents, at which point to add additional participants to the simple and when to stop gathering more data. even when our simple consists of one case only, e need to select the aspects of that case that we will focus on. Therefore, a qualitative study mush have a sampling plan describing the sampling parameters (participants, settings, events, process), and this plan should line up with the purposes of the study. Puch (2005) suggests that if it is not clear to us which cases, aspects, or incidents to study, it is usually worth devoting more work to developing the initial research questions.