Stein, Lincoln D.
Wiley, 1998
Buku Teks
Langer, Maria
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 SO
Norton, Peter
Microsoft Corp., 1985
Buku Teks SO