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Management Research Center Graduate School of Management FEUI, 2007
Artikel Jurnal
Engel, James F.
The Dryden Press , 1995
Buku Teks
Wells, William D.
John Wiley & Sons, 1996
Buku Teks SO
Schiffman, Leon G.
Pearson Education International, 2004
Buku Teks SO
Engel, James F.
Chicago Dryden Press, 1990
Buku Teks SO