Pascal Couderc and Kenneth Sillander, editors
Nias Press, 2012
Buku Teks
edited by G. N. Appell and Leigh R. Wright
Cornell University, 1978
Buku Referensi
Molnar, Andrea Katalin
KITLV Press , 2000
Buku Teks
Gallup, George, author
McGraw-Hill, 1982
Buku Teks
Robinson, Danielm, author
Lonely Publications Pty Ltd, 2011
Buku Referensi