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Citation Analysis

Basics of citation analysis, impact factors and scholarly publishing.

Terms and Definitions

Aggregate Cited Half Life: An indicator of the turnover rate for a body of work on a subject.

Cited Half-Life: "The cited half-life is the number of publication years from the current year which account for 50% of current citations received.  This figure helps you evaluate the age of the majority of cited articles published in a journal.  Each journal's cited half-life is shown in the Journal Rankings Window. Only those journals cited 100 times or more times have a cited half life" (Ladwig & Sommese, 2005).

Eigenfactor:  "Borrowing methods from network theory, ranks the influence of journals much as Google’s PageRank algorithm ranks the influence of web pages.  By this approach, journals are considered to be influential if they are cited often by other influential journals."

g-index:  Proposed by Egghe in 2006 to overcome a bias against highly cited papers inherent in the h-index. The g-index is the "highest number of papers of a scientist that received g or more citations, on average" (Schreiber, 2008a).

Google PageRank:  "PageRank evaluates two things: how many links there are to a web page from other pages, and the quality of the linking sites" (Cutts, 2009).

h-index:  The h-index, or Hirsch index, measures the impact of a particular scientist rather than a journal. "It is defined as the highest number of publications of a scientist that received h or more citations each while the other publications have not more than h citations each (Schreiber, 2008a)." The h-index is included in Web of Science, Scopus (ScienceDirect), and Google Scholar.  For example, a scholar with an h-index of 5 had published 5 papers, each of which has been cited by others at least 5 times.

Immediacy Index: The average number of times a journal article is cited in the year it is published. Can be useful for comparing journals on cutting-edge research.

Journal Impact Factor: The journal impact factor measures the importance of a journal and "is the average number of times articles from the journal published in the past two years have been cited in the JCR year" (Thomson Reuters, 2012).

How Impact Factor is Calculated "The annual JCR impact factor is a ratio between citations and recent citable items published. Thus, the impact factor of a journal is calculated by dividing the number of current year citations to the source items published in that journal during the previous two years" (from an essay originally published in Current Contents, June 20, 1994, now titled "The Thomson Reuters Impact Factor").

Journal Self-Citation: "A self-citation is a reference to an article from the same journal.  Self-citations can make up a significant portion of the citations a journal gives and receives each year" (Thomson Reuters, 2012).

Related Journals: Calculated using the number of citations from the selected journal title, total number of articles in the related journal, and total number of citations from the citing journal.  Uses the number of citations from one journal to another to determine a relationship.

Self-Citation: "The practice of self-citation can be considered at many levels, including author self-citation, journal self-citation, and subject category self-citation.  This may increase the impact factor artificially" (American Standards for Journals and Research, Evaluation Methodology).

Unified Impact Factor: Useful when a journal title changes because the impact factor is generally affected for two years.  You can view title changes in Journal Citation Reports by clicking on the Journal Title Changes link on one of the following pages: Journal Search, Journal Summary List, or Marked Journal List.  The Thomson Reuters Master Journal List: Journal Coverage Changes is also available from the Thomson Reuters website.


See the Further Reading tab in this LibGuide.

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