1. Free and Unequal: The Biological Basis of Individual Liberty. Austin: University of Texas Press, 1953.
2. Developmental Tasks and Education. New York: Longmans, Green and Co., 1952. p. 13.
3. Op. cit., pp. 21–22.
4. “Primary Mental Abilities,” American Association for the Advancement of Science, Centennial. Baltimore: Horn-Shafer Co., 1950.
5. Psychosocial Development of Children. New York: Family Service Association of America, 1951. pp. 49–50.