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 Factor. JAMA.2006; 295(1):90-93. doi:10.1001/jama.295.1.90.
The 5-year Impact Factor is the average number of times articles from the journal published in the past five years have been cited in the JCR year. It is caclulated by dividing the number of citations in the JCR year by the total number of articles published in the five previous years.
The 5-year Impact Factor is available only in JCR 2007 and subsequent years.
The Aggregate Impact Factor for a subject category is calculated the same way as the Impact Factor for a journal, but it takes into account the number of citations to all journals in the category and the number of articles from all journals in the category.
An aggregate Impact Factor of 1.0 means that that, on average, the articles in the subject category published one or two years ago have been cited one time. The median Impact Factor is the median value of all journal Impact Factors in the subject category.
For comparing journals specializing in cutting-edge research, the immediacy index can provide a useful perspective.
The Immediacy Index is the average number of times an article is cited in the year it is published.
The Immediacy Index is calculated by dividing the number of citations to articles published in a given year by the number of articles published in that year.
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.
Watch this video tutorial to learn how to find journals impact factors.
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).
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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 in UM Libraries collections.
