Waller, Jenny
Pustaka Binaman Pressindo, 1994
Buku Referensi
Lawson, Joseph W.R., II
American Management Association;;, 1998
eBooks
Carpendale, Jeremy
Blackwell Publishing, 2006
Buku Teks
Thompson, Frank J.
Thomson - Wadsworth, 2003
Buku Teks
Modern Business Report , 1985
Buku Teks