American Council on Education, 1964
Buku Teks
Schlossberg, Nancy K.
Jossey-Bass Publishers, 1989
Buku Teks
Jessey Bass Publishers, 1978
Buku Teks
Harris, Seymour E.
McGraw-Hill Book Company, Inc., 1962
Buku Teks
edited by Max M. Russell
Macmillan, 1973
Buku Referensi