De Vries, Mary Ann
Prentice-Hall, 1991
Buku Referensi
Boston: Houghton: 1993,
Buku Referensi
Bredow, Miriam
Gregg Publishing, 1959
Buku Referensi
Stroman, James
American Management Association, 2008
eBooks
Stroman, James
American Management Association, 2012
eBooks