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Bibliometrics and Altmetrics: Measuring the Impact of Knowledge: Impact Factors

DEFINITION #1: Impact Factor

The Impact Factor is based on an algorithm used by Web of Science to determine how important a given journal is in its field.

How is Impact Factor (IF) calculated?

The journal Impact Factor is the average number of times articles from the journal published in the past two years have been cited in the Journal Citation Reports (JCR) year:

A = the number of times that articles published in that journal in 2010 and 2011, were cited by articles in indexed journals during 2012.
B = the total number of "citable items" published by that journal in 2010 and 2011. ("Citable items" are usually articles, reviews, proceedings, or notes; not editorials or letters to the editor.)
2012 impact factor = A/B


Be aware that 2012 impact factors are actually published in 2013; they cannot be calculated until all of the 2012 publications have been processed by the indexing agency.

Further reading:

Garfield E. The History and Meaning of the Journal Impact FactorJAMA.2006; 295(1):90-93. doi:10.1001/jama.295.1.90.

A Humorous Overview of Impact Factors

Is this joking video an entirely accurate portrayal of impact factors? No. It is, however, representative of the frustration that academic publishing often entails. Choosing (or having to) publish a paper in a journal with a low impact factor is not always indicative of the quality of either, but it may feel that way - and be treated that way.

Now Seriously... How to Find Impact Factors?

Watch these video tutorials to learn more about Journal Impact Factors and how to interpret them.


What is Web of Science?

Web of Science Logo

Web of Science is a database maintained and owned by Thomson Reuters, most famous for providing journals with an Impact Factor (or IF) as part of its Journal Citation Reports (JCR).

Overview of Metrics Theory

Eugene Garfield       The idea of the impact factor was first introduced by Eugene Garfield in 1955. He is an American scientist, one of the founders of bibliometrics and scientometrics.

His book Citation indexing - its theory and application in science, technology, and humanities (1979) is available through the University System of Maryland Libraries. 

Issues and Controversy

Many aspects of Impact Factor recommend it as a measure: it's convenient, can purport to be objective (numbers are numbers) and is widely accepted as valid. However, the measure has its detractors. Some of the points of protest are listed below.

  • Since faculty want to publish in journals with a high Impact Factor, new journals may have a difficult time becoming established.
  • Some fields trend toward much higher Impact Factors than others (neuroscience tends to rate much higher than mathematics).
  • Some sub-fields may trend toward higher Impact Factors than others. A more specialized journal may be less likely to be cited than a general one, but an author would have very valid reasons for publishing in that less cited journal.
  • Review articles/journals (which offer no unique content, but provide handily citable summaries of other work) and practices such as self-citation may inflate Impact Factor.
  • Citation does not always correlate with quality or agreement (someone may cite an article to tear it apart).
  • An article or journal may be widely used by practitioners, who do not tend to cite. The impact is thus "invisible."
  • Worst comes to worst, a very good article may be published in a very bad journal.

Source: Duncan, L. ISI and Impact Factors. [Accessed June, 2014]