1. Maney AC, Pace R, Morrison DF: A factor analytic study of the need for institutionalization: Problems and populations for program development. Am J Ment Defic 69;374–384, 1964.
2. Shellhaas MD, Nihira K: Factor analysis of reasons retardates are referred to an institution. Am J Ment Defic 74;171–179, 1969
3. Penrose LS: Biology and Mental Defect, rev. ed. New York, Grune and Stratton, 1962.
4. Foale M: The special difficulties of the high grade mentally defective adolescent. Am J Ment Defic 60;867–877, 1956.
5. Beier DC: Behavioral disturbances in the mentally retarded, in Stevens HA, Huber R (eds): Mental Retardation. Chicago, University of Chicago Press, 1964.