The Journal Citation Reports, first published in 1975, is an annual compendium of citation data that provides a systematic and objective means to assess influence and impact at the journal and category levels. It contains reports on citation performance for science and
social science journals and the relationships between citing and cited journals. To
receive a Journal Impact Factor a journal must be covered in the Science Citation Index Expanded or Social Sciences Citation Index of the Web of Science. Only journals covered in these citation indexes are eligible to appear in Journal Citation Reports (JCR) and receive a Journal Impact Factor (JIF).
How is the JCR used?
The Journal Impact Factor was originally developed by Drs. Eugene Garfield and Irving H. Sher as a metric to aid in selection of additional journals for the newly created Science Citation Index. Today librarians continue to use the JCR as a tool in building and managing their journal collections. Publishers use the JCR to gauge journal performance and assess their competitors.
How is the Journal Impact Factor calculated?
The JIF is defined as citations to the journal in the JCR year to items published in the previous two years, divided by the total number of scholarly items, also known as citable items, (these comprise articles and reviews) published in the journal in the previous two years.
Journal Impact Factor Numerator
The numerator of the JIF consists of any citation to the journal as defined by the title of the journal, irrespective of what item in the journal might be cited. Each cited reference in a scholarly publication is an acknowledgement of influence. JCR therefore aggregates all citations to a given journal in the numerator regardless of cited document type. The citations that comprise the JIF numerator are drawn from the journal and proceedings indexes in Web of Science Core Collection (Science Citation Index Expanded, Social Sciences Citation Index, Arts & Humanities Citation Index, Emerging Sources Citation Index, and both the Science and Social Science and Humanities editions of the Conference Proceedings Citation Index). Citations from the Book Citation Index do not contribute toward JCR metrics.