For a more complete discussion of the erosion of library purchasing power, see

Anthony M. Cummings, Marcia L. Witte, William G. Bowen, Laura O. Lazarus, and Richard H. Ekman. University Libraries and Scholarly Communication A Study Prepared for The Andrew W. Mellon Foundation. Association of Research Libraries, 1992.

Available on-line at http://etext.lib.virginia.edu/reports/mellon/mellon.html