1. Breakwell, M. G., Hammond, S. & Fife-Schaw, C. (1995) (Eds). Research Methods in Psychology. London: Sage Publications.
2. Coleman, R. (2000). Living Longer: The New Context for Design. London: The Design Council.
3. Dillma, D. A. (1978). Mail and Telephone Surveys: The Total Design Method. New York: Wiley-Interscience Publication.