New Jersey, 1969
Buku Teks
Michelson, William, author
Addison-Wesley Publishing , 1970
Buku Teks
edited by Philip M. Hauser and Leo F. Schnore
John Wiley & Sons, 1965
Buku Teks
Artikel Jurnal
Dore, R.P., author
University of California Press , 1958
Buku Teks