Links to SAGE readings have been provided, non-SAGE readings are suggested and you may be able to find these via your university’s library.
For a methodological rationale for why case study designs are a sound approach and how they contribute to theory building, this paper is essential reading:
On choice of method, see this paper for an interesting critique of the emphasis in UK sociology of health on in-depth interviews:
On the choice of inductive/deductive designs, this paper is interesting on the rationale for qualitative research which is testing a model. The example is research using the Normalisation Process Theory Model, which is the subject of case study 13.2.
Macfarlane, A. and O'Reilly-de Brún, M. (2011) ‘Using a theory-driven conceptual framework in qualitative health research’, Qualitative Health Research, ;22(5):607–18. doi: 10.1177/1049732311431898. Epub 2011
The rather more pragmatic view on sample sizes for interview studies is from Guest et al, cited in the chapter: