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
Contains information on:
Recent trends in bogus metrics and predatory publishers encourage scholars to be very cautious about publishing claims regarding impact. There has been a call for what can be considered negative metrics. The Center for the Study of Interdisciplinarity has developed some lists and they appear in the following publications:
There is an increase in predatory sources that do not honor peer review and other standard methods of professional collaboration in scholarly publishing activities. This has extended to conferences as well as invitations to serve on editorial boards, etc. You can verify the sources in these sources: