Lemay, Michael C., author
Wardsworth, 2006
Buku Teks
Viola, Richard H.
W.B. Saunders Company, 1977
Buku Teks
Wells, Henry, author
Harvard University Press, 1969
Buku Teks
Artikel Jurnal
Agranoff, Robert, author
Georgetown University Pres, 2012
Buku Teks