Journal Impact Factor

From The Embassy of Good Science

Journal Impact Factor

What is this about?

A journal’s ‘Impact Factor’ (IF) gives an indication of journal influence. The IF is a measure of the number of citations divided by the number of published articles in a journal.[1] It is calculated for an entire year, taking into account number of citations of the articles published in the last two years, and divided with a number of publications in last two years. For example, the 2018 IF of a journal reflects the number of times the articles published in the journal in 2016 and 2017 were cited, divided by the number of articles actually published in the journal in 2016 and 2017.

  1. Garfield E. The history and meaning of the journal impact factor. Jama. 2006;295(1):90-3.

Why is this important?

Impact factors are important because they provide a measure of quality of a scientific journal.[1] The idea is that journals with higher IFs are read more frequently, have more of an impact within a field, and are of higher quality. They are also important because some academic institutions ask for publications in journals with high IFs for acquiring a PhD or advancement.[2] Journal IFs are calculated each year by Thomson Scientific and published by Journal Citation Reports.

Impact factors, however, can be manipulated. Examples of practices that influence IF are self and cartel citations, limitations of citable items, acceptance of more review articles.[3] Self-citation is a practice of citing one’s own work, to artificially increase a number of citations. Citation cartel is a practice of mutual citing between journals to increase their IF.[4] Editors can also insist that newly submitted manuscripts cite some of the works already published in that journals. Journals can limit a number of citable items, and not include them in the IF analysis. For example, letter to editor is a type of publication that is often referenced, and journals get the citation. But if it’s not included in the citable items, it could increase the IF. Journals can also choose to accept more review articles, which are often cited more, and can increase their IF that way.

It’s also important to note that it takes at least three years to calculate IF of the journal, and IF cannot be calculated for new journals. Because of all this, IF should be used cautiously when determining the quality of a journal, and other bibliometric data should be considered before making the final decision.[5][6]

  1. Garfield E. The history and meaning of the journal impact factor. Jama. 2006;295(1):90-3.
  2. Casadevall A, Fang FC. Impacted science: impact is not importance: MBio. 2015 Oct 13;6(5):e01593-15. doi: 10.1128/mBio.01593-15. eCollection 2015 Sep-Oct.
  3. Sharma M, Sarin A, Gupta P, Sachdeva S, Desai AV. Journal impact factor: its use, significance and limitations. World J Nucl Med. 2014;13(2):1450-147.
  4. Fister I, Perc M. Toward the Discovery of Citation Cartels in Citation Networks. Frontiers in Physics. 2016;4(49).
  5. Ioannidis JP, Boyack KW, Small H, Sorensen AA, Klavans R. Bibliometrics: Is your most cited work your best? Nature. 2014;514(7524):561-2.
  6. Time to remodel the journal impact factor: Nature. 2016 Jul 28;535(7613):466. doi: 10.1038/535466a.

For whom is this important?

What are the best practices?

Advance data mining techniques can help identify impact factor manipulation. See this article.

Other information

Virtues & Values
Good Practices & Misconduct