Impact Factor

What is "impact factor"?

Impact factor is a measure of the frequency with which the "average article" published in a given scholarly journal has been cited in a particular year or period and is often used to measure or describe the importance of a particular journal to its field. The Thomson-Reuters (formerly Institute for Scientific Information (ISI)) ranks, evaluates, and compares journals within subject categories and publishes the results in Journal Citation Reports.  The new rankings come out in the Spring, for the previous year's journals.  Three years worth of data are required to calculate a Journal Impact Factor.

The formula to determine the 2007 impact factor for a journal would be calculated as follows:

A = the number of times articles published in the journal during 2006-7 were cited by other journals during 2008
B = the number of articles or reviews that were published in the journal during 2006-7

2007 Impact factor for a journal = A/B

How to find a journal's impact factor or relative importance

From the library homepage, click on "Online Research Resources (Databases)"

Library Homepage

In Online Research Resources search for "Journal Citation Reports"

Online Research Resources

 

Click on the link that says "in Thomson ISI"

Online Research Resources

Select the Science or Social Science Edition, select a year, and choose to view a group of journals, search for a specific journal, or view all journals. You may view a group of journals by Subject Category (such as Agricultural Engineering, Astronomy, or Biology), by Publisher, or by Country/Territory.

Journal Citation Reports

Controversy

Impact factors have a huge, but controversial, influence on the way published scientific research is perceived and evaluated. Numerous criticisms have been made of the system:

  1. Journal impact factors depend on the research field: high impact factors are likely in journals covering large areas of basic research and less likely in more subject-specific journals.
  2. Although Journal Citation Reports includes some non-English journals, the index is heavily skewed toward English-language journals, leaving out important international sources.
  3. Researchers may be more likely to pursue fashionable topics that have a higher likelihood of being published in a high-impact journal than to follow important avenues that may not be the as popular.

Alternative ways of ranking journals

Learn more

Register to attend a workshop.

Or, if you can't attend a workshop, download the presentation: (Powerpoint) or (PDF). 

Monastersky, R. (2005). The number that's devouring science. The Chronicle of Higher Education, 52(8), A12. Available at: http://chronicle.com/free/v52/i08/08a01201.htm

Lange, L. L. (2002). The impact factor as a phantom; is there a self-fulfilling prophecy effect of impact? Journal of Documentation, 58(2), 175-184. Available at: http://www.emeraldinsight.com/10.1108/00220410210425449