Theil, H., author
Nort-Holand, 1964
Buku Teks
Brown, Robert Goodell, author
New York, N.Y., Holt, Rinehart and Winston
Buku Teks
Masse, Pierre
Prentice-Hall, 1962
Buku Teks
Grove, J.M.
Longmans, 1962
Buku Teks
Directorated for Economic Co-operation and Development , 1971
Buku Teks