1. Birren , James and Schaie , K. W. 1977.The Psychology of Aging, 580–605. New-York: Van Nostrand Reinhold Company.
2. Bolles , Richard N. 1978.The Three Boxes of Life, 5–60. Berkeley: Ten Speed Press.
3. Dewey , John . 1966.Democracy and Education, 49–62. New York: Macmillan Company.