Artikel Jurnal
Sommerlad, Elizabeth, author
Australian National University Press, 1976
Buku Teks
Allyn and Bacon, Inc., 1975
Buku Teks
Huxley, Aldous
New York, Harper & Brothers, 1956
Buku Teks
Jolly, D., author
World Health Organization, 1992
Buku Teks