Adler, Bill
Jones-Irwin, 1985
Buku Teks
Johns, Dean
Strategic Information and Research Development Centre , 2010
Buku Teks
Ripley, William Z.
Little, Brown, and Company, 1927
Buku Teks
Crabb, Peter R.
McGraw-Hill, 2003
Buku Teks
Baruch, Hurd
Acropolis Books ltd., 1971
Buku Teks