An impact factor is a measure of the importance of scientific journals. It is calculated each year by the Institute for Scientific Information for those journals which it tracks, and the factors are published in the Journal Citation Report. Impact factors have a huge, but controversial, influence on the way published scientific research is perceived and evaluated.
The impact factor is generally calculated based on a three-year period. For example, the 2003 impact factor for a journal would be calculated as follows:
- A = the number of times articles published in 2001-2 were cited in tracked journals during 2003
- B = the number of articles published in 2001-2
- 2003 impact factor = A/B