Goetsch, David L., author
Pearson-Prentice Hall, 2005
Buku Teks
International Labour Office, 1969
Buku Teks
Koren, Herman, author
Lewis Publishers, 1996
Buku Referensi
Reese, Charles D., author
CRC Press, Taylor and Francis Group, 2009
Buku Teks
Baldwin Spencer Building, 1994
Buku Teks