Gupita, Rajat, foreword
Harvard Business School, 1996
Buku Referensi
Bowman, Donald M.
McGraw-Hill , 1963
Buku Teks
Brown, Wilfred
Heinemann, 1971
Buku Teks
Savage, Christopher I.
Hutchinson, 1975
Buku Teks
Mund, Vernon A.
Appleton-Century-Crofts, 1971
Buku Teks