Clarke, John I., author
Pergamon Press, 1979
Buku Teks
Demko, George J., author
McGraw-Hill, 1970
Buku Teks
edited by John I. Clarke
Pergamon Press, 1984
Buku Teks
Browne, G.S., author
F.W. Chesire, 1960
Buku Teks
edited by Bernard Berelson
Voice of America, 1975
Buku Teks