Buchari Alma, author
Alfabeta, 2007
Buku Teks
Buchari Alma, author
Alfabeta , 2014
Buku Teks
Trisakti International Center for Service studies FE-Usakti, 2006
Majalah, Jurnal, Buletin
Rambat Lupiyoadi, author
Salemba Empat, 2001
Buku Teks
Ririn Trin Ratnasari, author
Ghalia Indonesia, 2011
Buku Teks