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Citation Analysis: Terms and Definitions

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, eigenfactor.org 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.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 and Scopus. 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 a measure of the frequency with which the 'average article' in a journal has been cited in a particular year or period" (Thomson Reuters, 2008).

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)

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, 2008)

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..."

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.

Attribution

Much of the content of this guide is based on a guide created at University of Michigan Library and which can be viewed here. Thank you to the group that created that guide and allowed us to make use of the content for our own guide.

Subject Guide

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Ilana Stonebraker
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