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Sciences - Citations Resources and Guidelines: Impact Factors

This L.guide was adapted from Miami University - Oxford Ohio Citation guide.

Impact factor (Adopted from University of Washington)

"An Impact Factor is one measure of the relative importance of a journal, individual article or scientist to science and social science literature and research. Each index or database used to create an impact factor uses a different methodology and produces slightly different results, revealing the importance of using several sources to judge the true impact of a journal's or scientist’s work. Included on this page is information on Journal Impact Factor, Author Impact Factor, and Article Impact Factor.

Informed and careful use of these impact data is essential, and should be based on a thorough understanding of the methodology used to generate impact factors. There are controversial aspects of using impact factors:

  • It is not clear whether the number of times a paper is cited measures its actual quality.
  • Some databases that calculate impact factors fail to incorporate publications including textbooks, handbooks and reference books.
  • Certain disciplines have low numbers of journals and usage. Therefore, one should only compare journals or researchers within the same discipline.
  • Review articles normally are cited more often and therefore can skew results.
  • Self-citing may also skew results.
  • Some resources used to calculate impact factors have inadequate international coverage.
  • Editorial policies can artificially inflate an impact factor.

Tools that measure Citation or Journal Impact (This guide includes content adapted with permission from Robin Kear, Liaison Librarian, University of Pittsburgh.)

Eigenfactor (URL: http://www.eigenfactor.org/ )

The Eigenfactor Score calculation is based on the number of times articles from the journal published in the past five years have been cited in the JCR year, but it also considers which journals have contributed these citations so that highly cited journals will influence the network more than lesser cited journals.  References from one article in a journal to another article from the same journal are removed, so that Eigenfactor Scores are not influenced by journal self-citation.

Article Influence (Article Influence uses Thomson Reuters (ISI Web of Knowledge) citation data.)
The Article Influence Score calculates measures the relative importance of the journal on a per-article basis. It is the journal's Eigenfactor Score divided by the fraction of articles published by the journal. That fraction is normalized so that the sum total of articles from all journals is 1.

The mean Article Influence Score is 1.00. A score greater than 1.00 indicates that each article in the journal has above-average influence. A score less than 1.00 indicates that each article in the journal has below-average influence.

In 2006, the top journal by Article Influence score is Annual Reviews of Immunology, with an article influence of 27.454. This means that the average article in that journal has twenty seven times the influence of the mean journal in the JCR.

Impact Factor  (Uses Thomson Reuters citation data. In Journal Citation Reports.)

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.

The Impact Factor is calculated by dividing the number of citations in the JCR year by the total number of articles published in the two previous years. An Impact Factor of 1.0 means that, on average, the articles published one or two year ago have been cited one time. An Impact Factor of 2.5 means that, on average, the articles published one or two year ago have been cited two and a half times. Citing articles may be from the same journal; most citing articles are from different journals.

The journal Impact Factor was developed by Eugene Garfield at the Institute for Scientific Information (ISI), now owned by Thomson Reuters.

Journal Metrics (Link)  (Uses Elsevier citation data. In Scopus.)

The Journal Analyzer provides a view of journal performance using Scopus citation data and includes two new journal metrics - Source Normalized Impact per Paper (SNIP) and SCImago Journal Rank (SJR). Using citations from nearly 18,000 titles from 5,000 international publishers, the Journal Analyzer goes back to 1996.

SJR  
Uses Elsevier citation data. In Scopus or at http://www.scimagojr.com/index.php
SNIP  
Uses Elsevier citation data. In Scopus or at http://www.journalindicators.com/
Google Scholar Metrics Journal (Link)
Uses Google Scholar publication information from 2007-2011.
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