Ng, Kwok K.
McGraw-Hill, 1995
Buku Referensi
Walkerly, John F.
John Wiley & Sons, 1976
Buku Teks
Genn, Robert C.
Prentice-Hall, 1982
Buku Teks
edited by A.D. Austen, R.H. Neale
International Labour Office, 1995
Buku Referensi
Barber, Alfred W.
Parker Publishing Company, Inc., 1980
Buku Referensi