Titmuss, Richard M.
George Allen and Unwin, 1983
Buku Teks
Kennedy, Richard
Macmillan Publishing Co. Inc, 1982
Buku Teks
Titmuss, Richard M.
University of Toronto Press , 1962
Buku Teks
Boumol, William J.
Harvard University Press, 1952
Buku Teks
Heckscher, Gunnar
Buku Teks