Hanke, Lewis
D. Van Nostrand Company, 1959
Buku Teks
Perkins, Dexter
Harvard University Press, 1947
Buku Teks
Borror, Donald J., author
Houghton Mifflin, 1976
Buku Referensi
Kinmel, Lewis H.
Brookings Institution , 1950
Buku Teks
Mandell, Lewis
. Institute for Social Reserach University of Michigan , 1972
Buku Teks