Impact factor. Calculation[edit] In any given year, the impact factor of a journal is the average number of citations received per paper published in that journal during the two preceding years.[1] For example, if a journal has an impact factor of 3 in 2008, then its papers published in 2006 and 2007 received 3 citations each on average in 2008.
The 2008 impact factor of a journal would be calculated as follows: A = the number of times that articles published in that journal in 2006 and 2007, were cited by articles in indexed journals during 2008. B = the total number of "citable items" published by that journal in 2006 and 2007. ScholarOne - Science - Thomson Reuters. Master Journal List - Science - Thomson Reuters. ResearcherID.com.