Journal's Impact Factor
The Impact Factor is tracked by the Institute for Scientific Information. This is a measure of the frequency with which the "average article" in a journal has been cited in a particular year.
| 1999 | 2000 | 2001 | 2002 | 2003 | 2004 | 2005 | 2006 | 2007 | 2008 | 2009 | 2010 | |
| Impact Factor | 1.268 | 1.006 | 0.813 | 0.892 | 0.672 | 0.803 | 1.219 | 1.234 | 1.467 | 1.463 | 1.576 | 1.995 |