Pick, James B., author
Westview , 1989
Buku Referensi
Dullemen, Inez van, author
Querido, 1988
Buku Teks
Vaillant, George C., author
Penguin Books, 1944
Buku Teks
Frigon, Normand L.
N.Y. American Management Association , 1996
Buku Teks
Benda, Harry Jindrich, author
Yale University, 1965
Buku Teks