Some books
Research Design
J. W. Creswell, “Research Design, Qualitative and Quantitative Approaches”, Sage Publications, 1994.
Case Studies
John Gerring. Case study research: principles and practices. Ed.Cambridge University Press, 2007
Qualitative Research
A. Strauss and J. Corbin. Basics of qualitative research: techniques and procedures for developing grounded theory. Thousand Oaks: Sage Publications, 1998.
Research groups