Stefferud, Alfred, editor
United States. Government Printing Office, 1966
Buku Referensi
Wood, Julia T., 1950-, author
Wadsworth and Cengage Learning, 2012
Buku Teks
Edwards, Edward, author
Thoemmes Press, 1996
Buku Referensi
Weitzman, David, author
Charles Seribner's Sond, 1994
Buku Referensi
Schramm, Wilbur, author
Standford University Press, 1961
Buku Teks