Preston, Lee E., author
IBER (Institute of Business and Economic Research), 1966
Buku Teks
Appleton-Century-Crofts, 1967
Buku Teks
Ferber, Robert
McGraw-Hill Book Co., Inc. , 1949
Buku Teks
Livingstone, James M.
Macmillan, 1977
Buku Teks
Prout, T.P.
Ekpping Gower Press c. 1973,
Buku Teks