Gorman, Alfred H.
Allyn and Bacon, 1969
Buku Teks
The British Council, 1980
Buku Teks
Manurung, Novi Ernalita
Fakultas Psikologi Universitas Indonesia, 1997
UI - Skripsi (Membership)
Dina Febrina Ekasari
Universitas Indonesia, 2003
UI - Skripsi (Membership)
Boyce, B. Ann
McGraw-Hill, 2003
Buku Teks