Journal Impact Factor

What it is

Journal Impact Factor (JIF) is the mean citation rate for articles published in research journals. JIF is calculated by dividing the number of citations to all document types (as JIF numerator) by the number of articles and reviews (as JIF denominator) published by the journals included in Web of Science Core Collection indexes in the prior 2 years. JIF is reported each year in the Journal Citation Reports published by Clarivate Analytics.

How it works

JIF is a journal-level metric that can be used to: - Compare journals with journals. It doesn’t represent the citation impact of individual articles in the journal. The use of the JIF as an inference tool for individual articles is an example of the ecological fallacy.

Compare journals in similar fields. Different research fields have different citation practices. To avoid unfair JIF comparisons, only journals in the same or similar fields should be compared. To compare journals of different fields, some form of field normalization is necessary.
Compare journals of large sizes, or any size provided the underlying citation distribution is approximately symmetric. Since citation distributions are often highly skewed (relatively few articles receive most citations, sometimes described as “the long tail”), comparison of journals of very different sizes should be avoided. This is because a blockbuster paper (e.g., a review paper) in a small journal can cause a spike in the JIF and lead to unfair comparisons.

What to keep in mind

The JIF has been published annually since 1975, and an extensive body of literature is available on its characteristics, limitations, and common misunderstandings related to its use. Some of the documented limitations are related to the metric itself, while some are related to the underlying data used to calculate the metric. Some commonly noted limitations of the JIF are as follows:

The Journal Impact Factor applies only to journals indexed in the Science Citation Index Expanded and/or Social Sciences Citation Index by Clarivate Analytics. Journals are reviewed using several criteria and not all journals are selected for inclusion in the Journal Citation Reports.
There is debate about the degree of transparency related to guidelines for the journals and article types selected for inclusion. Some claim there is not enough transparency while others feel that Clarivate’s documentation on the selection process is sufficient.
A related debate surrounds the differing scope of the numerator and denominator used for calculating the Journal Impact Factor. While the numerator includes all items published in a journal, the denominator includes only those deemed citable by JCR. Items (or document types) included in the denominator are article, review, and proceedings paper. Items like editorials, letters, and news items are excluded from the denominator. In particular, some take issue with the definition of a “citable item”.
The range of JIF values and JCR’s coverage varies by discipline, which makes context such as citation density and rates crucial for interpreting the JIF.
The JIF numerator includes citations to the journals in the calendar year.
Citations are counted only to items with a publication date from the prior two years. These citations are sourced from all item types included in Web of Science Core Collection indexes. From JCR 2021 (using 2020 data), citations from early access contents (consideration of first availability dates vs. publication dates) are used in calculating JIF.
Journals in the Arts and Humanities Citation Index are reportedly not given a JIF due to the long half-life of citations and references in them.
Review articles have a higher average citation rate than other types of articles and will influence the net value of the JIF accordingly.
Research published in journals written in languages other than English may be at a disadvantage, as studies have suggested that these journals are not included as often in the JCR.
Journals published in North America are reportedly disproportionately represented in the sources indexed by Journal Citation Reports.

Learn more

Clarivate Analytics. Journal Citation Reports
Clarivate Analytics. Adding Early Access content to Journal Citation Reports Choosing a prospective model
Seglen, P. O. (1997). Why the impact factor of journals should not be used for evaluating research. BMJ, 314(7079), 497. https://doi.org/10.1136/bmj.314.7079.497
Editors, T. Pl. M. (2006). The Impact Factor Game. PLOS Medicine, 3(6), e291. https://doi.org/10.1371/journal.pmed.0030291
Waltman L and Traag VA. (2021). Use of the journal impact factor for assessing individual articles: Statistically flawed or not? [version 2; peer review: 2 approved]. F1000Research, 9:366 https://doi.org/10.12688/f1000research.23418.2

Journal Acceptance Rate
Citations, articles

References

Last updated April 2022