Kalijarvi, Thorsten V., author
Thomas Y. Crowell, 1954
Buku Teks
edited by Arend Lijphart
Allyn and Bacon, 1966
Buku Teks
Organski, A.F.K., author
Alfred A. Knopf, 1969
Buku Teks
MacKay, R.A., author
The Ryerson Press, 1935
Buku Teks
Ball, Alan R., author
Macmillan, 1974
Buku Teks