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Nutrition: Impact Factor

Impact Factor

Impact factor, or Journal 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. Impact factor was originally developed by Eugene Garfield, the founder of Institute of Scientific Information, which is now a part of Thomson Reuters. Journal Impact Factor can be found in Thomson Reuter's Journal Citation Reports. Over the years various organizations have been created similar journal-level metrics, such as SCImago Journal & Country Rank.

This page describes how to find impact factor in Journal Citation Reports by Thomson Reuters.

A Humorous Overview of Impact Factors

More Information

The Impact Factor is based on an algorithm used by Web of Science to determine how important a given journal is in its field.

How is Impact Factor (IF) calculated?

The journal Impact Factor is the average number of times articles from the journal published in the past two years have been cited in the Journal Citation Reports (JCR) year:

A = the number of times that articles published in that journal in 2010 and 2011, were cited by articles in indexed journals during 2012.
B = the total number of "citable items" published by that journal in 2010 and 2011. ("Citable items" are usually articles, reviews, proceedings, or notes; not editorials or letters to the editor.)
2012 impact factor = A/B

 

Be aware that 2012 impact factors are actually published in 2013; they cannot be calculated until all of the 2012 publications have been processed by the indexing agency.

Further reading:

Garfield E. The History and Meaning of the Journal Impact Factor. JAMA.2006; 295(1):90-93. doi:10.1001/jama.295.1.90.

How to Find Impact Factor

5-Year Impact Factor

The 5-year Impact Factor is the average number of times articles from the journal published in the past five years have been cited in the JCR year. It is calculated by dividing the number of citations in the JCR year by the total number of articles published in the five previous years.

The 5-year Impact Factor is available only in JCR 2007 and subsequent years.

Aggregate Impact Factor

The Aggregate Impact Factor for a subject category is calculated the same way as the Impact Factor for a journal, but it takes into account the number of citations to all journals in the category and the number of articles from all journals in the category.

An aggregate Impact Factor of 1.0 means that that, on average, the articles in the subject category published one or two years ago have been cited one time. The median Impact Factor is the median value of all journal Impact Factors in the subject category.

Impact Factor is used to:

  • measure the importance or rank of a journal by calculating the times it's articles are cited.
  • evaluate the relative importance of a journal in general or in its field.
  • compare journals in the same field.
  • help you decide in which journals to publish.
  • reflect the changing status of a journal, as the impact factor increases or declines over time.

                                                                                       

Journal Citation Reports

Thomson Reuters (formerly Institute for Scientific Information (ISI)) ranks, evaluates, and compares journals within subject categories and publishes the results in Journal Citation Reports. Journal Citation Reports provides ranking for journals in science, technology, and the social sciences. For every journal, the database collects and/or calculates information such as:

  • citation/article counts
  • impact factor
  • immediacy index
  • cited half-life
  • citing half-life
  • source data listing
  • citing journal listing
  • cited journal listing
  • publisher information
  • subject categories

 

Find Journal Citation Reports (JCR)

Follow the instructions below to find the Journal Citation Reports using the Library's resources.

  1. Begin at the Library homepage.
  2. Click on "Databases,"
    • Then select  the letter "J" for Journal Citation Reports from the index.
  3. Scroll to Journal Citation Reports" and click on the hyperlinked title.
  4.  Then authenticate your credentials providing your username and password.

Find the Impact Factor

  1. Once in the database you will see a list of Journals by Rank which shows you journals with the highest impact factor.
  2. On the left side you can choose search criteria, like impact factor range, year, and if the journal is open access.
  3. Select the edition you would like to search. You can search for the JCR Science edition (SCIE) and the JCR Social Sciences edition (SSCI).
    • It is important to choose the right edition based on your subject area, as you won't be able to see specific journals if you choose the wrong one. Once you have finished selecting what to search, click Submit.
  4. You can't access impact factors from last year because the calculations only happen every two years (i.e. if the current year is 2013 the farthest you can go back is 2011). Most people choose the most current year they can access.
  5. Other options you can search by are:
    • Journals limited by the subject area, publisher, or geographic region.
    • View all journals in order to browse.
    • Search for a specific journal if you already know its title

Once you find a journal, the JCR gives you information about the journal, including the journal's abbreviations, how often it is published each year, the publisher, and the ISSN. The Journal Citation Report also provides the impact factor both for the last two and five-year periods. You may notice that JCR provides Eigenfactor scores as well.

Controversy

Many people have questioned the legitimacy of impact factor. Here are a few reasons why:

  • Based only on quantitative information
    • Impact factor focuses purely on the number of citations a journal has. There is no consideration of qualitative sources that have become important in today's world.
    • Impact factor fails to incorporate more recent ways of sharing and using research, includeing Twitter mentions and posts, citation management downloads, and newspaper and community information.
  • Only indexed journals
    • Because impact factor is based on citations in only indexed journals, it fails to incorporate statistics from journals that might not be indexed and other sources like conference papers (which are important in the social sciences).
  • Basic concepts
    • Basic or summary information is usually cited the most in academia. That means that journals that publish articles with basic information are more likely to have higher impact factors. Journals that publish obscure or innovative information might not have as high of an impact factor.
    • Some argue that impact factor is encouraging scholars to stick with mainstream topics and research.
  • Influence
    • Scholars don't always have to cite something for it to be influential. Sometimes researchers just read something and it influences them, regardless of if they cite it in a future paper or piece of research.
  • International Sources
    • The journals in the ISI are mostly published in English. This means that many international sources aren't included in the conversation.
  • Skewing Impact Factor
    • It has been argued that journals have the ability to skew impact factor for their own journal. Before publishing an author, they will ask the author to cite more articles within their journal so that their impact factor goes up. This is NOT a common occurrence but instead something we should be aware

Immediacy Impact

For comparing journals specializing in cutting-edge research, the immediacy index can provide a useful perspective.

The Immediacy Index is the average number of times an article is cited in the year it is published.

  • The journal Immediacy Indexindicates how quickly articles in a journal are cited.
  • The aggregate Immediacy Indexindicates how quickly articles in a subject category are cited.

The Immediacy Index is calculated by dividing the number of citations to articles published in a given year by the number of articles published in that year.