Artikel Jurnal
Jeanne H. Ballantine, Joan Z. Spade, editors
SAGE Publications, 2015
Buku Teks
McGraw-Hill , 1973
Buku Teks
International Labour Organisation
International Labour Organisation, 1983
Buku Referensi
Lawson, Hal A., author
Allyn and Bacon, 1981
Buku Teks