The most well-known metric for assessing a journal is Journal Impact Factor or Impact Factor. Created in 1969 as a means to help librarians make collection development decisions, Journal Citation Reports (JCR) publishes their annual results ranking journals in the areas of science, technology, and social sciences.

Limitations:

• Subscription required to view rankings (K's Library does NOT subscribe to JCR)
• Limited to the citation data of journals indexed in Web of Science
• Not field-normalized, meaning that it does not take into account variations in citation behaviors across different disciplines. The Impact Factor should therefore only be used when making comparisons within the same discipline.
• Arts & Humanities journals are being added, but don't receive a Journal Impact Factor score (see Journal Citation Indicator section below)

Journal Impact Factor (JIF) measures the frequency with which content published in a journal was cited in other journals during the two previous years.

Calculation of a 2020 IF of a journal:

a = the number of times "citable items" published in 2018 and 2019 were cited by indexed journals during 2020.
b = the total number of "citable items" published in 2018 and 2019.

a / b = 2020 impact factor

Example:

Let's say in the years 2018 and 2019 there were 100 citable items published in a journal. In 2020, those 100 items were cited 400 times.

We divide the total citations (400) by the total items (100) to get a 2020 Journal Impact Factor of 4.0. In other words, items published in the previous two years received an average of 4 citations during the JCR year.

Beginning with their 2021 release, JCR is now including journal titles from the Arts & Humanities Citation Index and the Emerging Sources Citation Index (ESCI). These title won't receive a Journal Impact Factor but instead they will use the new Journal Citation Indicator (JCI).

Journal Citation Indicator (JCI):

• Available for all journal titles; the only metric used for Arts & Humanities titles
• A discipline-normalized measurement of journal citation impact
• Based on the previous 3 years of data