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Research Impact Metrics

What are Journal Impact Factors, and how are they calculated?

The Journal Impact Factor (JIF) is a way to measure the relative impact of a particular journal within its field, based on the average number of times an article published will be cited in the near future. The data is based on the journals and citing sources (journals, proceedings, books) in the Web of Science Core Collection, with impact factors available for more than 11,500 journals in the Science and Social Science Citation Indexes.

The impact factors are released annually in the Journal Citation Reports and calculated like this:

If a journal published 2,000 articles and reviews (citable items) in 2015 and 2016, and those articles and reviews (plus anything else the journal published those two years) get cited 20,000 times in the articles, conference proceedings and books in 2017, then the 2017 impact factor for that journal is 10  If the journal also publishes pieces like letters, those do not get counted in the citable items, but citations to those pieces will get counted in the numerator..

Where can I find Journal Impact Factors?

The impact factors are published in Journal Citation Reports (JCR). There's one report for the sciences, and another for the social sciences. There is no JCR for the arts and humanities journals indexed in Web of Science. You can also access JCR from the Web of Science interface.

In JCR, you can search for a particular title, or "Browse By Journal" to bring up a ranked list of journals in one or more categories to compare impact factors. Some disciplines are divided into multiple categories (7 for Chemistry, 11 for Psychology, etc.) and many journals are assigned to multiple categories. The subject lists may also help you identify journals in your field for potential article submissions.


What data can I get from JCR?

For each journal, you'll get:

  • The most recent Journal Impact Factor and associated data, including a citation distribution and list of the citable items ranked by times cited. Also the impact factors for previous years, to see trends over time.
  • The assigned subject categories for the journal, with each linked to the ranked impact factor list for that category.

Full list of indicators:


Many of these indicators are also available (and sortable) at the subject category level. Use customize to set up which ones you want to see.

Considerations when using journal impact factors, and how not to use them

Journal Impact Factors tell you nothing about the impact of the author or particular article, and they should not be used as a measure of a researcher's impact. They should not even be the sole factor when evaluating the quality of the journal.

  • From ClarivateThe Journal Impact Factor should not be used without careful attention to the many phenomena that influence citation rates, as for example the average number of references cited in the average article. The Journal Impact Factor should be used with informed peer review. In the case of academic evaluation for tenure it is sometimes inappropriate to use the impact of the source journal to estimate the expected frequency of a recently published article. Again, the Journal  Impact Factor should be used with informed peer review. Citation frequencies for individual articles are quite varied.
  • The San Francisco Declaration of Research Assessment (DORA) identifies the inefficiencies of using JIFs for research assessment.and calls for "the need to eliminate the use of journal-based metrics, such as Journal Impact Factors, in funding, appointment, and promotion considerations."

Impact factors vary widely across disciplines and should not be compared with each other. Here are the impact factors for journals that are the highest in their given category.  However, they may be ranked lower in other assigned categories.

  • General & Internal Medicine 79.260
  • Multidisciplinary Sciences: 41.577
  • Multidisciplinary Psychology: 26.364
  • Telecommunications: 20.230
  • Geochemistry & Geophysics: 13.529
  • Clinical Psychology: 13.278
  • Biomedical Engineering: 8.806
  • Economics: 7.863
  • Linguistics: 4.880
  • History and Philosophy of Science: 2.568: 

There are several factors that affect impact factors:

  • Biomedical and related sciences tend to skew higher. 
  • Review journals also skew higher, and are often the journals that top their respective categories. There are often fewer articles (citable items), and these articles can get cited heavily.  Compare these two journals: one with a higher impact factor, but fewer citable items and all of them review articles.  


     
  • Citations to items that are not counted as citable items, such as editorial letters, do get counted in to total citations (numerator).
  • Disciplines that rely more on books as a major research output are also affected. Books that are not indexed in Web of Science are not factored into the total citations, and it may be several years before the book citing the articles even gets published. 

Impact factors can be subject to manipulation.

  • Clarivate will suppress JCR metrics for journals due to "anomalous citation patterns" such as unusually higher number of self cites to boost the JIF numerator, or a high percentage of citations in that numerator originating from one journal.

What about other journal-level metrics?

They exist, but are less well-known. Eigenfactor and Article Influence scores are also listed in Journal Citation Reports. The same caveats apply: do not compare journals across disciplines, and that journal rankings should not be used to evaluate the impact of articles or researchers. 

  • Eigenfactor
    ​From Clarivate: The value of the Eigenfactor is similar to the Journal Impact Factor or the 5-year Journal Impact Factor. Unlike those, the Eigenfactor assigns weight or value to each earned citation, according to the citedness of the citing journal. Consider two journals: Journal A is highly cited; Journal B is poorly cited. Cites coming from Journal A are given greater weight when the Eigenfactors for journals B-Z are being calculated and cites from Journal B are given less weight when calculating Eigenfactors for journals A & C-Z.
     
  • Article Influence Score
    From Clarivate: The Article Influence determines the average influence of a journal's articles over the first five years after publication.  It is calculated  by multiplying the Eigenfactor  by 0.01 and dividing by the number of articles in the journal, normalized as a fraction of all articles in all publications.  This measure is roughly analogous to the 5-Year Journal Impact Factor in that it is a ratio of a journal’s citation influence to the size of the journal’s article contribution over a period of five years. A score greater than 1.00 indicates that each article in the journal has above-average influence.
  • SCImago Journal Rank
    SCImago is another journal indicator that takes into account the number of citations for a journal and the importance of the journals citing those articles. It's similar to the Eigenfactor, but is based on Scopus citation data, while Eigenfactor is based on Web of Science.
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