Hove Psychology Press 1997
Buku Referensi
Nababan, Melva Ratna Rulida
Fakultas Ilmu Pengetahuan Budaya Universitas Indonesia, 1983
UI - Skripsi Membership
New York : Holt, Rinehart and Winston, 1995,
Buku Teks
Holschuh, Louis W.
New York: St. Martin`s Press, 1991,
Buku Teks
by L.G. Alexander ... [and others]
Longman, 1975
Buku Teks SO