Impact Factor–What does it mean?

Nowadays, the Clarivate Analytics (formerly Thomson Reuters) Impact Factor is considered an established measurement of quality for the evaluation of journals [1]. But what is the history behind it?

The idea of an impact factor was first mentioned in Science magazine in 1955 [2]. Five years later, the experimental Genetics Citation Index project begun, leading to the publication of the 1961 Science Citation Index® (SCI®). Clarivate Analytics citation indexes used computer-compiled statistical reports not only on the output of journals but also in terms of citation frequency, laying the ground for what we know today as “Impact Factor” [3].
After using journal statistical data in-house to compile the Science Citation Index for many years, Clarivate Analytics began to publish Journal Citation Reports® (JCR®). The JCR provides quantitative tools for ranking, evaluating, categorizing, and comparing journals, the impact factor being one of these [3].

A journal’s impact factor is calculated based on two elements: the numerator, which is the number of cites in the current year to any items published in the journal in the previous two years; and the denominator, the number of substantive articles (source items) published in the same two years [3]:

IF 2016 = 2016 cites to articles published in 2014–2015/number of articles published in 2014–2015.

We are pleased to report the 2016 Journal Impact Factors, which were published by Clarivate Analytics in the latest edition of the Journal Citation Reports®. For 21 out of 27 journals covered in the Science Citation Index Expanded (SCIE) the Impact Factor increased compared to the previous year.
Coatings received a first Impact Factor; Cancers was included in the Science Citation Index Expanded earlier this year and is due to receive an Impact Factor in the 2018 release of the Journal Citation Reports. For detailed information about the new impact factors, please visit our website.