...Available at: www.cdc.gov/od/ ads/authorship.htm. Cochran, WG 1 977 Sampling Techniques. New York: Wiley. Coyne, IT 1997 Sampling in qualitative research. Purposeful...merging or clear boundaries. Journal of Advanced Nursing 26(3):623-630. Crabtree, B. E, and WL Miller 1992 Doing Qualitative Research. London: Sage. Creswell.JW...