Fridman, Leonid, editor
Springer, 2011
eBooks
edited by Jacqueline A. Kalley, Elna Schoeman, Marlene Burger
University of South Africa, 2005
Buku Teks
The Population Reference Bureau, Inc., 1976
Buku Teks
Keegan, Warren J., author
Warren Keegan Associaties, 1995
Buku Teks
Salas, Rafael M., author
Pergamon Press, 1979
Buku Teks