Buchsbaum, Walter H., author
Prentice-Hall, 1987
Buku Referensi
Coombs, H. C.
Macmillan, 1981
Buku Teks
Coombs, William E.
F.W. Dodge Co. , 1958
Buku Teks
editors, Cameron Hazlehurst and J. R. Nethercote
National University Press, 1977
Buku Teks
Coombs, H.C.
Australian National University Press, 1978
Buku Teks