Yin, Robert K., author
Rajawali, 2013
Buku Teks
Scholz, Roland W., author
Sage, 2002
Buku Teks
edited by F.C. Bartlett
Kegan Paul, Trench, 1946
Buku Teks
Williams, Thomas Rhys
Holt, Rinehart and Winston, 1967
Buku Teks
Kelly, Paul J., author
John Wiley & Sons, 1979
Buku Teks