Clarke, Linda, author
Institute of Personnel and Development, 1993
Buku Teks
Davidson, Kenneth M.
West Publishing Company, 1974
Buku Teks
Mansfield, Peter, author
Optima , 1995
Buku Teks
Hand, D.J., author
John Wiley & Sons, 1981
Buku Teks
Fredman, Sandra, author
Oxford University Press, 2011
Buku Teks