What is Impact Factor?

There are many different measures of a journal's importance in a field. One of these is Impact Factor, which is a measure of the average frequency that articles from the journal are being cited in other articles. The Impact Factor of a journal in a particular year is published in Journal Citation Reports, which is available online through Web of Science (on the header).

In any given year, the journal Impact Factor is the average number of times articles from the journal published in the past two years have been cited in articles published that year. A high Impact Factor number is an indication that articles published in this journal are on average cited more frequently than those in a journal with a low Impact Factor. 

Why is the Impact Factor of a journal important?

Since articles in journals with higher Impact Factors are being cited more frequently (on average), these journals can be considered to be the leading edge in research in their field. Therefore, it is important that you are familiar with the content of these journals for your own research. Also, depending on the academic institution, promotion and tenure committees sometimes give more weight or credit to authors who publish in journals with higher Impact Factor, so PhD students who aspire to publish research and attain tenured faculty status in the future should keep Impact Factor in mind when deciding which journals to send their research for publication.

Cautions and Controversies

Impact Factor is not the only way to measure a journal's importance, and there are some criticisms of this 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

• Eigenfactor.org: Ranking and mapping scientific knowledge
  • A journal's Eigenfactor score is the measure of the journal's total importance to the scientific community. For more information about how this is measured, see the Eigenfactor metrics page at Eigenfactor.org.
  • A journal's Article Influence score is a measure of the average influence of each of its articles over the first five years after publication. For more information about this, see the FAQs page at Eigenfactor.org.

Counting citations is often called "citation analysis." In your scholarly research, you may need to gauge the importance of a publication by counting the number of times it has been cited by other scholars. When you count the number of times an article has been cited in published research, you gain information about that article's impact on its discipline. If an article has a high number of citations, you may conclude that it has been the subject of discussion or criticism in its discipline. In addition, finding the list of articles that have cited an article can help you find more information about your research topic, a process called "citation chasing."

"Counting citations" sounds simple; however, citation analysis tools count citations from different sets of publications. When you are performing a citation analysis, you may need to use several different databases to count citations, in order to fully capture an article's impact. Web of Knowledge (Web of Science) and Scopus are two databases which maintain citation statistics on the articles indexed in these databases. For search tips and additional citation analysis options, see the Library's Citation Analysis webpage.

You can also set up citation alerts in these databases to notify you when there is a new citation of a particular article or author. Many scholars use these alerts to find out when their own work is cited, in addition to tracking new citations of other authors' articles.