Peterson, Wallace C.
W.W. Norton & Co., 1962
Buku Teks
Fishman, Betty G., author
Thomas Y. Crowell, 1969
Buku Teks
Artikel Jurnal
International Labour Office, 1964
Buku Teks
Gupta, Syamaprasad, author
The Johns Hopkins University Press, 1977
Buku Teks