What is the Impact Factor of a journal?

Journal Impact Factors

Journal Impact Factor is from Journal Citation Report (JCR), a product of Thomson ISI (Institute for Scientific Information). JCR provides quantitative tools for evaluating journals. The impact factor is one of these;

 it is a measure of the frequency with which the "average article" in a journal has been cited in a given period of time.

The impact factor for a journal is calculated based on a three-year period, and can be considered to be the average number of times published papers are cited up to two years after publication. For example, the impact factor 2007 for a journal would be calculated as follows:

A = the number of times articles published in 2005-6 were cited in indexed journals during 2007

B = the number of articles, reviews, proceedings or notes published in 2005-6

impact factor 2007 = A/B

(note that the impact factor 2006 will be actually published in 2007, because it could not be calculated until all of the 2007 publications had been received. Impact factor 2007 will be published in 2008)