edited by G. N. Appell and Leigh R. Wright
Cornell University, 1978
Buku Referensi
Molnar, Andrea Katalin
KITLV Press , 2000
Buku Teks
Gallup, George
McGraw-Hill, 1982
Buku Teks
Robinson, Danielm
Lonely Publications Pty Ltd, 2011
Buku Referensi
Mackinnon, John Ramsay
[publisher not identified], [date of publication not identified]
Buku Teks