Association of Research Libraries (ARL)

Starting with 2005–06 data, ARL is calculating a Library Investment Index (previously named Expenditures-Focused Index) as an alternative to the historical index known as the ARL Membership Criteria Index. The Library Investment Index replaces the public availability of the ARL Membership Criteria Index. The Library Investment 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 an index for the university library members of ARL. The index is a summary measure of relative size among the university library members of the Association. The sole purpose of the index used to be a membership criterion for the Association of Research Libraries; it currently serves as one indicator of potential for membership. The ARL Membership Criteria 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 allowed ARL to evaluate potential new members and track the maintenance of membership requirements.

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).