impact factor

Impact Factor

Understanding journal impact factors

What they are

An impact factor is a metric for ranking scientific journals [1].

Impact factors are calculated for every two-year period by dividing the number of times articles were cited by the number of articles that are citable [2].

The following is a list of the top five highest-impact journals in 2014 [3].

JournalTotal citesImpact factor
CA: A Cancer Journal for Clinicians18,594115.840
New England Journal of Medicine268,65255.873
Chemical Reviews137,60046.568
Nature Reviews Drug Discovery23,81141.908

Why they are important

Journals with high impact factors are often considered more prestigious than lower-ranking journals. They also have more visibility in the field, which could increase your article’s visibility. Furthermore, your career advancement (e.g. securing funding, job applications at certain institutions) can greatly hinge on the number of times you have published in high impact journals [1].

Why they aren’t everything

The scientific community is becoming more aware of the limitations of impact factors. For example, a journal’s impact factor may only reflect a small fraction of its published papers. A 2005 editorial in Nature reported that 89% of the journal’s impact factor—32.2 at the time—could be attributed to 25% of the papers published during the relevant period [1]. Furthermore, there are ways for journals to “game” (i.e. manipulate) impact factors. “Over 20% of researchers have been pressured by journal editors to modify their articles in ways that manipulate the reputation of the journal [4].” As such, the scientific community are starting to move away from using impact factors as a means to rank a researchers’ scholarly contributions [1].

In conclusion

While it can be advantageous to publish in high impact journals, it is more important to choose a journal based on its aims and scope.


1. Verma IM. Impact, not impact factor. PNAS. 2015;112(26):7875–7876.

2. University of Illinois at Chicago. Measuring Your Impact: Impact Factor, Citation Analysis, and other Metrics: Measuring Your Impact. Available from: [Accessed 8th February 2016].

3. Thomas Reuteurs. InCites Journal Citation Reports™ (2014). Available from: [Accessed 8th February, 2016].

4. Rice C. How journals manipulate the importance of research and one way to fix it. Curt Rice –Science in Balance. Weblog. 2012 April 6. Available from: [Accessed 8th February, 2016].