Definition: The journal impact factor measures the importance of a journal by calculating the number of times its articles are cited.
How Impact Factor is Calculated: The calculation is based on a two-year period and involves dividing the number of times articles were cited by the number of articles that are citable.
Experts stress that there are limitations in using impact factors to evaluate a scholar's work. There are many reasons cited for not relying on impact factor alone to evaluate the output of a particular individual. Among these are the following:
According to Jim Testa, a researcher for ThomsonReuters Scientific, the most widespread misuse of the Impact Factor is to evaluate the work of an individual author (instead of a journal). "To say that because a researcher is publishing in a certain journal, he or she is more influential or deserves more credit is not necessarily true. There are many other variables to consider." (interview 6/26/2008 in Thomson Reuters blog entry)
For an overview on the topic, see the Introduction under the Journal Rankings tab.
To use Journal Citation Reports, follow the steps below:
For more information about Journal Citation Reports, click on the Information for New Users located in the upper right hand corner of the database opening page, or view the Journal Citation Reports tutorial created by Thomson ISI.
To get detailed information about a journal, use UlrichsWeb. There is information about whether a journal is "refereed" (same as peer-reviewed) near the top of the listing for each journal.