The purpose of price indexes for print library materials is to measure as accurately as possible on a periodic basis the extent of price changes. A price index is an economic indicator that in systematic fashion for a period of time and at fixed intervals of time (usually annual) provides for the derivation of average prices and citation of changes in terms of index numbers. Price indexes describe the essential characteristics of various forms of library materials (as set forth in the standard) so that the same characteristics are measured periodically. A set of prices indexes is intended to meet administrative needs for budgeting, materials price analysis, and other purposes in libraries and other organizations with similar information needs. Price indexes represent a standard measurement of the market dynamics of a particular publication type (format) rather than reflecting exact pricing for a specific library, publisher, or situation.