Approaches to sampling and case selection in qualitative research: examples in the geography of health

This paper focuses on the question of sampling (or selection of cases) in q ualitative research. Although the literature includes some very useful disc ussions of qualitative sampling strategies, the question of sampling often seems to receive less attention in methodological discussion than questions of how data is collected or is analysed. Decisions about sampling are like ly to be important in many qualitative studies (although it may not be an;i ssue in some research). There are varying accounts of the principles applic able to sampling or case selection. Those who espouse 'theoretical sampling ', based on a 'grounded theory' approach, are in some ways opposed to those who promote forms of 'purposive sampling' suitable for research informed b y an existing body of social theory. Diversity also results from the many d ifferent methods for drawing purposive samples which are applicable to qual itative research. We explore the value of a framework suggested by Miles an d Huberman [Miles, M., Huberman,, A., 1994. Qualitative Data Analysis, Sage , London.], to evaluate the sampling strategies employed in three examples of research by the authors. Our examples comprise three studies which respe ctively involve selection of: 'healing places'; rural places which incorpor ated national anti-malarial policies; young male interviewees, identified a s either chronically ill or disabled. The examples are used to show how in these three studies the (sometimes con flicting) requirements of the different criteria were resolved, as well as the potential and constraints placed on the research by the selection decis ions which were made. We also consider how far the criteria Miles and Huber man suggest seem helpful for planning 'sample' selection in qualitative res earch. (C) 2000 Elsevier Science Ltd. All rights reserved.