Kohler, Heinz
Holt, Rinehart and Winston, 1968
Buku Teks
Homan, Paul T., author
Harcourt, Brace and Company, 1958
Buku Teks
Robinson, Marshall A., author
Brookings Institution, 1962
Buku Teks
Robinson, Marshall A., author
Brookings Institution, 1962
Buku Teks
Leftwich, Richard H., author
Rienhard and Winston, 1969
Buku Teks