The case against (only) using metrics for collection management

I’m currently working with Sarah Sutton at Emporia State University on launching a survey to get a sense of how librarians use altmetrics, including for collection development purposes. (Is it useful to know if a book has been cited in a policy document, even if it’s rarely circulated, so you don’t deaccession it? Can monitoring online activity for all scholarship–even articles that a library doesn’t have subscription access to–help librarians make much quicker purchasing decisions for articles and journals that patrons might request?