Thomas, Spencer
East Sussex Wayland , 1979
Buku Teks
Feld, Werner J., author
Pergamon Press, 1980
Buku Teks
Buckley, Peter J., author
Macmillan, 1978
Buku Teks
Lubis, Todung Mulya, author
Universitas Indonesia, 1977
Buku Teks
International Labur Organization, 1992
Buku Teks