one of the most well-known methods in evaluation of science is Scientometrics. In this field, through citation based indicators, can find out value and scientific attention to articles and journals. IF (Impact Factor) and II (Immediacy index) are Two of the most common of these indicators that offer in JCR.
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. 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 all items published in that journal in 2006 and 2007, were cited by indexed publications during 2008.
B = the total number of "articles" published by that journal in 2006 and 2007.
2008 impact factor = A/B.
(Note that 2008 impact factors are actually published in 2009; they cannot be calculated until all of the 2008 publications have been processed by the indexing agency.)
The immediacy index is calculated based on the papers published in a journal in a single calendar year. For example, the 2005 immediacy index for a journal would be calculated as follows:
A = the number of times articles published by the journal in 2005 were cited in indexed journals during 2005
B = the number of articles, reviews, proceedings or notes published by the journal in 2005
2005 immediacy index = A/B