Starting with 2005–06 data, ARL is calculating an Expenditures-Focused Index as an alternative to the ARL Membership Criteria Index. The Expenditures-Focused Index replaces the public availability of the ARL Membership Criteria Index. The Expenditures-Focused Index is highly correlated with the Membership Criteria Index and less affected by changes in the collections variables. The methodology behind this new index is described by Bruce Thompson in his October 2006 paper, "Some Alternative Quantitative Library Activity Descriptions/Statistics that Supplement the ARL Logarithmic Index."
The principles and procedures for academic library membership in ARL are based partly on quantitative data that provide a view of the range of resources deployed among the existing members of the Association.
Each year, ARL calculates a Membership Criteria Index formula and index for the university library members of ARL. The Membership Criteria Index is a summary measure of relative size among the university library members of the Association; its sole purpose is to serve as a membership criterion for those institutions. This index comprises the five quantitative data elements in which ARL university libraries most resemble one another, and does not attempt to measure a library's services, quality of collections, or success in meeting the needs of users. The Membership Criteria Index allows ARL to evaluate potential new members as well as to track the maintenance of membership requirement for current members.
A detailed description of the ARL Membership Criteria Index is available in The ARL Library Index and Quantitative Relationships in the ARL, by Kendon Stubbs (Washington, DC: ARL, 1980). Available from ARL Publications.
