1. Morris, J. N.: The Uses of Epidemiology (2d ed.). Baltimore: Williams & Wilkins, 1964, p. 14.
2. Tringo, J. L.: The hierarchy of preference toward disability groups, J. Spec. Educ, 4:295–306, 1970.
3. Leighton, D. C, Harding, J. S., Macklin, D. B., et al.: The Character of Danger. Vol. III of the Stirling County Study. New York: Basic Books, 1963.
4. Langner, T. S., and Michael, S. T.: Life Stress and Mental Health. Vol. II of The Midtown Manhattan Study. Thomas A. C. Rennie Series in Social Psychiatry, Vol. II. London: Collier Macmillan, 1963.
5. Schwab, J. J., Fennell, E., and Warheit, G. J.: The epidemiology of psychosomatic disorders, Psychosomatics, 15:88–93, 1974.