1. Beck, A. T. Depression: Causes and Treatment. Philadelphia: University of Pennsylvania Press, 1967.
2. Belcher, M . The measurement of loneliness: A validation .stud.v of the Belcher Extended Loneliness Scale (BELS). (Doctoral dissertation, Illinois Institute of Technology, 1973). (University Microfilms No. 74-16.990).
3. Bradley, R. Measuring loneliness. Unpublished doctoral dissertation, Washington State University, 1969.
4. Cron bach.L. J. Essentials of ps.vchologica 1 testing. New York: Harper & Row, 1960.
5. Donson. C. & Georges, A. Lonely-landand bedsitter-land. Bala, North Wales: Chapples, 1967.