From the Association of Research Libraries:
ARL has released the Library Investment Index for 2013–2014, the latest in this annual summary measure of the relative size of the university library members of the Association.
Although similar to the ARL Membership Criteria Index in reflecting the investments made in research libraries, the ARL Library Investment Index is less affected by the electronic availability of content and, consequently, the rapidly changing context of library collections. Neither index attempts to measure a library’s services, quality of collections, or success in meeting the needs of users. The ARL Library Investment Index has been calculated beginning with data from 2002–2003.
The final data tables that are published in the Chronicle [of Higher Education] are available for free download from the ARL Statistics website. An interactive version of the data is also freely available on the ARL Statistics site.
Direct to Final Data Tables (XLS)
Direct to Interactive Analytics
Direct to Data For Individual Libraries (2003-)