David, Paul I
Brookings Institution, 1957
Buku Teks
Cayer, N. Joseph., author
Wadsworth/Thomson Learning, 2004
Buku Teks
Bernstein, Marver H.
The Brookings Institution, 1958
Buku Teks
Thompson, Frank J., author
Thomson - Wadsworth, 2003
Buku Teks
edited by Steven W. Hays, Richard C. Kearney
Prentice-Hall, 1990
Buku Teks