Ranking by ISI Impact Factor (2001 JCR — May 2003)

[A] >10
[B] 10 - 4
[C] 4 - 2
[D] 2 - 0.5
[E] <0.5

ISI defines 'impact factor': The journal impact factor is a measure of the frequency with which the "average article" in a journal has been cited in a particular year. The impact factor will help in evaluating a journal's relative importance, especially when comparing it to others in the same field. The impact factor is calculated by dividing the number of current citations to articles published in the two previous years by the total number of articles published in the two previous years.