Levinson, Harold M., author
John Wiley & Sons, 1966
Buku Teks
edited by D.C. Hague
St. Martin's Press, 1962
Buku Teks
International Labour Office , 1985
Buku Teks
Dilts, David A., author
McGraw-Hill, Irwin, 2007
Buku Teks
Carrell, Michael R., author
Prentice-Hall, 2001
Buku Teks