Hawley, Amos H.
The University of Chicago Press, 1986
Buku Teks
Hawley, Amos H.
The Ronald Press, 1950
Buku Teks
Watson, Richard A.
Harcourt, Brace and World, 1969
Buku Teks
Zipf, George Kingsley
Hafner, 1965
Buku Teks
George, Carl J.
McGraw-Hill, 1974
Buku Teks