Gannon, Michael, author
Prentice-Hall, 1982
Buku Referensi
Ng, Kwok K., author
McGraw-Hill, 1995
Buku Referensi
Walkerly, John F.
John Wiley & Sons, 1976
Buku Teks
Genn, Robert C., author
Prentice-Hall, 1982
Buku Teks
edited by A.D. Austen, R.H. Neale
International Labour Office, 1995
Buku Referensi