Goldman, A. E., & McDonald, S. Schwartz. (1987). The group depth interview: principles and practices. Englewood Cliffs: Prentice-Hall.
Greenbaum, T. L. (1987). The practical handbook and guide to focus group research. Lexington, MA: Lexington Books, DC Heath and Co.
Morgan, D. L. (1988). Focus groups: Qualitative research. Qualitative Research Methods Series 16. Thousand Oaks, CA: Sage.
Morgan, D. L., & Krueger, R. A. (1998).The focus group kit. Thousand Oaks, CA: Sage.
Stewart, D. W., & Shamdasani, P. N. (1990). Focus groups: Theory and practice. Thousand Oaks, CA: Sage.
Wells, W. D. (1974). Group interviewing. In R. Ferber (Ed.), Handbook of marketing research. New York: McGraw-Hill.