Lang, Robert E., author
Brookings Institution Press, 2003
Buku Teks
Drake, St. Clair
Harper and Row, 1962
Buku Teks
Ferriss, Hugh, author
Dover Publications, 2005
Buku Teks
Polk, William R. (William Roe), 1929-, author
St. Martin's Press, 1979
Buku Teks
Wolfe, Gerard R., author
McGraw-Hill, 1994
Buku Referensi