Journal impact factor (JIF)

The journal impact factor measures how often, on average, articles published in a given journal are cited, and is widely used as a proxy for that journal's prestige or influence within its field. It is published annually by Clarivate in the Journal Citation Reports.

It is calculated for a given year as the number of citations that year to articles the journal published in the two preceding years, divided by the number of citable articles the journal published in those same two years. A journal with a JIF of 5 received, on average, five citations per article from the prior two years' output. This differs from the h-index, which scores an individual researcher's output rather than a journal, and it says nothing about the citation count of any single article.

The impact factor is heavily used in bibliometrics to compare journals within a field and, controversially, as a proxy for the quality of individual papers or researchers who publish in them, a practice the San Francisco Declaration on Research Assessment (DORA) explicitly argues against. Known pitfalls include wide variation in typical impact factors across disciplines, making cross-field comparisons meaningless, and the fact that a small number of highly cited papers can inflate a journal's average well above what most of its articles individually receive.