Grasso, John T.
Carnegie Foundation, 1979
Buku Teks
Department of Health, education and welfare, 1964
Buku Teks
Marland, Sidney P., author
McGraw-Hill, 1974
Buku Teks
Antje Barabasch
Springer, 2012
eBooks
edited by Robert M. Hashway
Praeger, 1990
Buku Referensi