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Journal impact factor

An impact factor is a measure of the frequency that the "average article" published in a scholarly journal has been cited in a two or five year period. It is often used to measure or describe the importance of a particular journal in an academic discipline. Authors can use impact factors to evaluate journals to decide which to publish in. Impact factors were initially developed by the Institute for Scientific Information (ISI).

Calculating impact factors

The impact factor of a journal in a particular year is the number of citations received in the current year to articles published in the two preceding years divided by the number of articles published in the same two years. For example, Journal of Petrology has a 2012 impact factor of 4.714, which means that on average each of its 2010 and 2011 articles was cited 5.012 times in 2011.

Here's how that was calculated:

Cites in 2012 to items published in: 2011 294 Number of items published in: 2011 84
  2010 531   2010 91
  Sum: 825   Sum: 175

Calculation: Cites to recent items 825 = 4.714
  Number of recent items 175    

Finding impact factors

The primary tool for locating impact factors is the Web of Science database Journal Citation Reports.

JCR - Journal Citation Reports from Thomson's InCites

    ISI Web of Science
This resource is restricted to Virginia Tech users only  Screencast tutorials available for this resource

JCR - Journal Citation Reports from Thomson's InCites

Journal Citation Reports provides citation data for journals, and includes virtually all areas of science, technology, and social sciences. Journal Citation Reports can show you the most frequently cited journals in a field, highest impact journals in a field based on a calculated impact factor and Eigenfactor score, immediancy indexes, and largest journals in a field. 2000-2014.  

Full record

You can find impact factors for specific journals or journals within a field. New journals are tracked every year, but JCR by no means calculates impact factors for every journal published. Some journals not tracked by JCR calculate their own impact factors and post them on the journal's home page.

Connecting the dots across the research ecosystem

A white paper from Thomson Reuters (the provider of Journal Citation Reports) on uses and misuse of the impact factor.

Impact factors from Journal Citation Reports
Immediacy index on Journal Citation Reports