What they are
An impact factor is a metric for ranking scientific journals .
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 .
The following is a list of the top five highest-impact journals in 2014 .
|Journal||Total cites||Impact factor|
|CA: A Cancer Journal for Clinicians||18,594||115.840|
|New England Journal of Medicine||268,652||55.873|
|Nature Reviews Drug Discovery||23,811||41.908|
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 .
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 . 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 .” As such, the scientific community are starting to move away from using impact factors as a means to rank a researchers’ scholarly contributions .
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. Verma, I.M. (2015) Impact, not impact factor. Proceedings of the National Academy of Sciences, 112(26), pp.7875–7876.  The Board of Trustees of the University of Illinois. (2013) University of Illinois. Available at: http://researchguides.uic.edu/if [Accessed 08 February, 2016].  Thomas Reuteurs. (2014) InCites Journal Citation Reports™. Available at: www.iau-ahar.ac.ir/ahar/images/pdf/JCR_2014.xls [Accessed 08 February, 2016].  Curt Rice. (2012) Curt Rice – Science in Balance. Available at: http://curt-rice.com/2012/04/06/how-journals-manipulate-the-importance-of-research-and-one-way-to-fix-it/ [Accessed 08 February, 2016].