Porter, Gerald J.
Springer, 1996
Buku Teks SO
Leon, Steven J., author
Prentice-Hall, 1996
Buku Teks SO
White, Myron R.
Allyn and Bacon, 1968
Buku Teks
Sofwah Ahmad, author
Universitas Indonesia, 2012
UI - Skripsi Membership
Hall, James E., author
Brooks/Cole, 1971
Buku Teks