Johnson, Robert, author
PWS-Kent, 1984
Buku Teks
Mann, Prem S, author
John Wiley & Sons, 2013
Buku Teks
Haber, Audrey, author
Addison-Wesley , 1970
Buku Teks
Michael S. Lewis-Beck, editor
Sage Publications, 1993
Buku Referensi
Thurtone, L.L., author
Macmillan, 1925
Buku Teks