Wright, Samson
Oxford University Press, 1931
Buku Referensi
Heragu, Sunderesh S.
Sunderesh S., 2016
Buku Teks
Press, Frank
W.H. Freeman and Company, 1986
Buku Referensi
Weston, Paul B.
Prentice-Hall, 1977
Buku Teks
edited by R.J. Johnston, Derek Gregory, Geraldine Pratt, Michael Watts
Blackwell Publishing, 2000
Buku Referensi