Oehler, Karsten, author
McGraw-Hill, 2012
Buku Teks
Stein, Lincoln D., author
Wiley, 1998
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Langer, Maria, author
Osborne/McGraw-Hill, 1999
Buku Referensi
Central Statistical Office
Her Majesty`s Stationery Office, 1986
Buku Referensi
Conlan, Jim
John Wiley & Sons, 1984
Buku Teks