Schaffer, Richard
West , 1996
Buku Teks
Harvard Business School Press, 2000
Buku Teks
Buttler, Henry N.
South-Western Publishing Co., 1987
Buku Teks
Blackburn, John D., author
Richard D. Irwin , 1985
Buku Teks
Bearden, James H., author
Holt, Rinehart and Winston , 1969
Buku Teks