Skip to main content

Bibliometrics & Citation Tracking: Impact Factor

Paper on Impact Factor

Eugene Garfield, the creator of the journal Impact Factor, wrote an article outlining its history in 2006.

Variations of Citation Data

Like the Impact Factor, the Eigenfactor Score and Article Influence Score use ISI Web of Knowledge citation data to assess and track the influence of a journal in relation to other journals in the same discipline.

Aggregate Impact Factor

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.

What is a journal's Impact Factor?

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.

The Impact Factor is calculated by dividing the number of citations in the JCR year by the total number of articles published in the two previous years. An Impact Factor of 1.0 means that, on average, the articles published one or two year ago have been cited one time. An Impact Factor of 2.5 means that, on average, the articles published one or two year ago have been cited two and a half times. Citing articles may be from the same journal; most citing articles are from different journals.

The journal Impact Factor was developed by Eugene Garfield at the Institute for Scientific Information (ISI), now owned by Thomson Reuters.

Impact Factor uses Thomson Reuters (ISI Web of Knowledge) citation data.

Example of Impact Factor

The only way to access the Impact Factor is by using Journal Citation Reports (Oxford has subscription access).

An example of the journal with the highest impact factor in the subject History:

5-year Impact Factor

The 5-year journal 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.

Immediacy Index

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 journal Immediacy Index indicates how quickly articles in a journal are cited.
  • The aggregate Immediacy Index indicates how quickly articles in a subject category are cited.

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.