Binet, A., & Simon, T.The development of Intelligence in children. Trans. Elizabeth S. Kite . Baltimore : Williams & Wilkins , 1916.
2.
Clarke, A.M.Criteria and classification of mental deficiency. In A. M. Clarke, & A. D. B. Clarke (Eds.). Mental deficiency: The changing outlook . New York: The Free Press, 1965.
3.
Clausen, J.Ability structure and subgroups in mental retardation. Washington: Spartan Books, 1966.
4.
Clausen, J.Mental deficiency-development of a concept. American Journal of Mental Deficiency, 1967, 71, 727-745.
5.
Clausen, J.A comment on Halpern's note. American Journal of Mental Deficiency , 1968, 72, 950.
6.
Dingman, H.F., & Tarjan, G.Mental retardation and the normal distribution curve. American Journal of Mental Deficiency, 1960, 64, 991-994.
7.
Penrose, L.S.The biology of mental defect(3rd ed.) New York: Grune & Stratton, 1963.
8.
Sarason, S.B., & Doris, J.Psychological problems in mental deficiency. (4th ed.) New York: Harper, 1969.
9.
Seguin, E.Idiocy and its treatment by the physiological method. New York: William Wood, 1866.