Fraser, D.A.S.
John Wiley & Sons, 1967
Buku Teks
Tippett, L. H. C.
Williams and Norgate , 1952
Buku Teks
Yamane, Taro
New York University, 1967
Buku Teks
Croxton, Frederick E.
Prentice-Hall, 1960
Buku Teks
Johnson, Palmer O.
Rand McNally, 1959
Buku Teks