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Sheena Chaudhari 873 April 3, 2019

What is Impact Factor? How it is calculated?


The impact factor (IF), also denoted as Journal impact factor (JIF), of an academic journal is a measure of the yearly average number of citations to recent articles published in that journal.

The impact factor was devised by Eugene Garfield, the founder of the Institute for Scientific Information. Impact factors are being calculated yearly starting from 1975 for journals listed in the Journal Citation Reports.

In any given year, the impact factor of a journal is the number of citations, received in that year, of articles published in that journal during the two preceding years, divided by the total number of articles published in that journal during the two preceding years.

How Impact Factor is calculated?

$IF_y = \frac{Citations_{y-1} + Citations_{y-2}}{Publications_{y-1} + Publications_{y-2}}$

Impact Factor is used to evaluate the relative importance of journals within specific domains. The journal which has more review articles will have a higher IF. The higher the Impact factor, the more highly ranked the journal. It is one tool you can use to compare journals in a particular subject category.

For example, to calculate the IF of a journal XYZ in the year 2016, we would follow the following steps:

$IF_{2016}= \frac{Citations_{2015} + Citations_{2014}}{Publications_{2015} + Publications_{2014}}$

Suppose, we have the following values:
Citations2015 = 9753
Citations2014 = 1924
Publications2015 = 570
Publications2014 = 269
IF2016= (9753 + 1924) / (570 + 269) = 13.91

This means that, on average, XYZ’s papers published in 2014 and 2015 received roughly 14 citations each in 2016.

Also, please remember that 2016 impact factors are reported in 2017; they cannot be calculated until all of the 2016 publications have been processed by the indexing agency.

The impact factor is related to a specific time period. Therefore, it becomes possible to calculate it for any desired period. For example, the Journal Citation Reports (JCR) also includes a five-year impact factor, which is calculated by dividing the number of citations to the journal in a given year by the number of articles published in that journal in the previous five years.