New York Institute of Finance, 1988
Buku Teks
Statistics Division, Petroleum Information Service, 1968
Buku Referensi
Smith, Roy C., author
Harvard Business School Press, 1997
Buku Teks
Andersen, Dines
Copenhagen: Gyldendalske Boghandel, 1907
Buku Teks
American Psychiatric Press, 1984
Buku Referensi