Journal Impact Factor

Can apply to: Journals indexed in the Clarivate Science Citation Index Expanded and/or Social Sciences Citation Index

Metric definition: The Journal Impact Factor is a measure reflecting the annual average (mean) number of citations to recent articles published in that journal. An essay written by the Institute of Scientific Information (ISI), now Clarivate Analytics, states “The JCR provides quantitative tools for ranking, evaluating, categorizing, and comparing journals. The impact factor is one of these; it is a measure of the frequency with which the “average article” in a journal has been cited in a particular year or period. The annual JCRimpact factor is a ratio between citations and recent citable items published.”

Metric calculation: From Wikipedia: “In any given year, the impact factor of a journal is the number of citations received in that year by articles published in that journal during the two preceding years, divided by the total number of articles published in that journal during the two preceding years.” Citations are counted for all items in the journal, though the citations are divided by only the number of “citable items” within the journal, as defined by the creators of the Journal Citation Report (currently Clarivate Analytics). Citable items are restricted by document type to articles and reviews.

Data sources: Citation data used to calculate journal citations is sourced all citations found in the Web of Science Core Collections

Appropriate use cases: The JIF can be useful in comparing the relative influence of journals within a discipline, as measured by citations. Used appropriately and in conjunction with other metrics, the JIF can be useful in collection development decisions made by librarians. As with all metrics, the JIF should be presented with appropriate context.

Limitations: The JIF has been published annually since 1975, and an extensive literature is available on its characteristics, limitations, and common misunderstandings related to its use. Some commonly noted limitations of the JIF:

Inappropriate use cases:

Available metric sources: Journal Citation Reports

Transparency: The formula for calculating the JIF is public, though there is some debate about the transparency of how journals are selected for inclusion (see above). For those with subscription access to the JCR, a journal’s JCR listing includes a list of the counted items in the denominator.  The citation data network and the summarized values used for all metrics are available to subscribers for download.

Website: https://clarivate.com/products/journal-citation-reports/

Timeframe:  Recently, the JCR has been released about 6 months after the year in question. For example, the JIF for 2016 were released in June 2017.