Libraries monitor their collection strength using a variety of indicators.
There are numerous collection assessment tools that document for libraries how their collections and services compare with similar institutions. Disciplinary information such as Digital Humanities: Questions and Answers addresses many issues related to trends and research directions.
Examples may include OCLC's WorldCat Collection Assessment Tool, and Comparative Collection Assessment for Books.
Membership in national consortia such as the American Association of Universities (AAU) and the Association of Research Libraries (ARL) provide annual demographics about a library collection, size, staff and the operating costs.
The American Library Association and the The Bowker Annual of Library and Book Trade Information give statistical analysis of library resources.
For International impacts, there are a number of resources that describe library holdings, WorldCat, an international consortia of libraries; governmental funding structures, rankings and assessment exercises such as in the UK with SCONUL ; in Australia, Libraries Australia
This series of videos from Irish academics discuss some of the limitations of bibliometrics, and the importance of using a variety of methods to evaluate impact.
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