Langer, Maria, author
Osborne/McGraw-Hill, 1999
Buku Referensi
Stein, Lincoln D., author
Wiley, 1998
Buku Teks
Central Statistical Office
Her Majesty`s Stationery Office, 1986
Buku Referensi
Oehler, Karsten, author
McGraw-Hill, 2012
Buku Teks
Anderson, Chris, author
Headline Publishing Group, 2016
Buku Teks