Bibliometric analysis to identify core reference sources of virtual reference transactions

As the use of electronic reference sources becomes commonplace, virtual reference services are expanding in scope, modes, and popularity. Simultaneously, reference practices are evolving as well. One concept that may be challenged by these trends is the notion of the core reference collection. What are the sources that form this core collection, and what are its characteristics? Are similar sources used to answer users' questions in virtual and traditional reference? How do core collections of public and academic libraries differ? An analysis of 1851 e-mail and chat reference transactions from public and academic libraries reveals that the notion of a core reference collection persists in the world of virtual reference services. In both types of libraries, responses to patrons showed a skewed bibliographic distribution; librarians used a small group of sources to answer most of the questions. Almost all sources used were electronic. Academic libraries tended to make greater use of fee-based sources, but public libraries more often used sources freely-available on the Web.