edited by Harold F. Williamson
Prentice-Hall, 1955
Buku Teks
Robertson, Ross M., author
Harcourt, Brace & World, 1964
Buku Teks
Davis, Lance E.
Richard D. Irwin, 1965
Buku Teks
Colm, Gerhard, author
National Planning Association , 1961
Buku Teks
Reynold, Lloyd George
McGraw-Hill, 1981
Buku Teks