Understanding Journal-level Metrics
Web of Science has trademarked the term Journal Impact Factor (JIF), capturing the yearly mean number of citations of articles published in the previous two years in a given journal. For instance, if 200 articles were published in Journal XX during 2019-20, and in 2021 these articles were cited 100 times in total, Journal XX would have a JIF of 0.5 for 2021.
The Scopus database incorporates a journal-level metric calculated in a slightly different way: a journal's CiteScore is the number of citations to documents (articles, reviews, conference papers, book chapters, and data papers) [in that journal] over four years, divided by the total number of the same document types [in that journal] indexed in Scopus and published in those same four years.
- A journal's JIF or CiteScore will change every year, as the previous year's articles are taken into account.
- Any citations made in publications which aren't indexed by Web of Science or Scopus (books and journals with a small readership) won't be reflected in the journal level metrics in that database.
- A single very highly-cited article in a journal can temporarily skew the mean, giving the false impression that typical articles in that journal are more highly cited than is actually the case.
Both Web of Science and Scopus offer a percentile ranking for each subject discipline, to enable researchers to quickly identify the journals which score highly: a journal in the 90th percentile has a higher mean citation count than 90% of the journals in that discipline.
Citation patterns vary by discipline, so JIFs and CiteScores cannot be compared for journals in different subject areas. To counter this, both databases also offer a 'normalised' citation score for every journal, weighted according to typical citation patterns in the discipline.
Web of Science calls this metric the Journal Citation Indicator (JCI), and Scopus uses the term Source Normalised Impact per Paper (SNIP). A normalised score >1.0 means that articles in that journal are typically cited more frequently than would be expected in the discipline. A score of 1.5 shows that articles are cited 50% more frequently than expected.
(screenshot from CWTS Journal Indicators, 2022)
Finding Journal-level Metrics
Many journal publishers who are proud of the level of attention given to their papers promote their Impact Factor and/or CiteScore on their homepage. Interpret with care if the metric is undated, or there is no reference to the ranking within the discipline.
(2022 screenshots from the homepage of the journal Cell).
Authoritative sources which are free to access:
CWTS Journal Indicators. Created by academics at the University of Leiden in the Netherlands, using Scopus SNIP metrics (1999 to date) for journals in STEM disciplines. Search for a specific journal title or browse by discipline for a ranked list. The Impact Per Paper (IPP) metric is derived from the SNIP weighted for the size of the journal.
SCImago Journal Rank (SJR). Derived from Scopus citation scores by Spanish academics, the SJR measures weighted citations received by the serial. Citation weighting depends on subject field and prestige of the citing serial. Search by journal title or browse by discipline or region for a ranked list. Lists can be filtered by open access status to help authors identify the most impactful open access journals to publish in.
Dimensions. Search the free Dimensions database for a Source Title, to find the latest Scopus SNIP and SJR metrics, plus annual mean citations for the previous 10 years.
Journal Citation Reports. Derived from the Web of Science bibliographic databases, covering all disciplines. Search by journal title for the current Journal Impact Factor and five-year trend, plus a ranked list of the most highly-cited articles in that journal, and other analytics including evidence of how long attention persists for articles in the journal concerned (the 'citation half life'). Browse by (Subject) Category for a ranked list of titles.
Scopus. From the homepage, choose the Sources search interface (top right) to search for a specific journal title, or browse by subject area for a title list ranked by CiteScore.
Some professional bodies and media organisations publish their own (often subject-based) journal rankings, relying on expert judgement as well as bibliometrics. One of the best known is the UK Chartered Association of Business Schools' annual (ABS) Academic Journal Guide, categorising business and management journals from 1 (lowest) to 4* (highest) based on Web of Science and Scopus metrics plus consultation with societies and leading academics. The ABS guide is free to view on registration.